public DynamicQueryOptimizerResult SelectAppropriateIndex(
            string entityName,
            IndexQuery indexQuery,
            List <Explanation> explanations = null)
        {
            // There isn't much point for query optimizer of aggregation indexes
            // the main reason is that we must always aggregate on the same items, and using the same
            // aggregation. Therefore we can't reuse one aggregate index for another query.
            // We decline to suggest an index here and choose to use the default index created for this
            // sort of query, which is what we would have to choose anyway.
            if (indexQuery.AggregationOperation != AggregationOperation.None)
            {
                return(new DynamicQueryOptimizerResult("", DynamicQueryMatchType.Failure));
            }

            if (string.IsNullOrEmpty(indexQuery.Query) &&                                   // we optimize for empty queries to use Raven/DocumentsByEntityName
                (indexQuery.SortedFields == null || indexQuery.SortedFields.Length == 0) && // and no sorting was requested
                database.IndexDefinitionStorage.Contains("Raven/DocumentsByEntityName"))    // and Raven/DocumentsByEntityName exists
            {
                if (string.IsNullOrEmpty(entityName) == false)
                {
                    indexQuery.Query = "Tag:" + entityName;
                }
                return(new DynamicQueryOptimizerResult("Raven/DocumentsByEntityName", DynamicQueryMatchType.Complete));
            }

            var fieldsQueriedUpon           = SimpleQueryParser.GetFieldsForDynamicQuery(indexQuery).Select(x => x.Item2).ToArray();
            var normalizedFieldsQueriedUpon =
                fieldsQueriedUpon.Select(DynamicQueryMapping.ReplaceInvalidCharactersForFields).ToArray();
            var distinctSelectManyFields = new HashSet <string>();

            foreach (var field in fieldsQueriedUpon)
            {
                var parts = field.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
                for (int i = 1; i < parts.Length; i++)
                {
                    distinctSelectManyFields.Add(string.Join(",", parts.Take(i)));
                }
            }

            ExplainDelegate explain = (index, rejectionReason) => { };

            if (explanations != null)
            {
                explain = (index, rejectionReason) => explanations.Add(new Explanation
                {
                    Index  = index,
                    Reason = rejectionReason()
                });
            }


            // there is no reason why we can't use indexes with transform results
            // we merely need to disable the transform results for this particular query
            indexQuery.SkipTransformResults = true;
            var results = database.IndexDefinitionStorage.IndexNames
                          .Select(indexName =>
            {
                var abstractViewGenerator = database.IndexDefinitionStorage.GetViewGenerator(indexName);
                var currentBestState      = DynamicQueryMatchType.Complete;

                if (abstractViewGenerator == null)                                 // there is no matching view generator
                {
                    explain(indexName, () => "There is no matching view generator. Maybe the index in the process of being deleted?");
                    return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                }

                if (entityName == null)
                {
                    if (abstractViewGenerator.ForEntityNames.Count != 0)
                    {
                        explain(indexName, () => "Query is not specific for entity name, but the index filter by entity names.");
                        return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                    }
                }
                else
                {
                    if (abstractViewGenerator.ForEntityNames.Count > 1)                                     // we only allow indexes with a single entity name
                    {
                        explain(indexName, () => "Index contains more than a single entity name, may result in a different type being returned.");
                        return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                    }
                    if (abstractViewGenerator.ForEntityNames.Count == 0)
                    {
                        explain(indexName, () => "Query is specific for entity name, but the index searches across all of them, may result in a different type being returned.");
                        return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                    }
                    if (abstractViewGenerator.ForEntityNames.Contains(entityName) == false)                                     // for the specified entity name
                    {
                        explain(indexName, () => string.Format("Index does not apply to entity name: {0}", entityName));
                        return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                    }
                }

                if (abstractViewGenerator.ReduceDefinition != null)                                 // we can't choose a map/reduce index
                {
                    explain(indexName, () => "Can't choose a map/reduce index for dynamic queries.");
                    return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                }

                if (abstractViewGenerator.HasWhereClause)                                 // without a where clause
                {
                    explain(indexName, () => "Can't choose an index with a where clause, it might filter things that the query is looking for.");
                    return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                }

                // we can't select an index that has SelectMany in it, because it result in invalid results when
                // you query it for things like Count, see https://github.com/ravendb/ravendb/issues/250
                // for indexes with internal projections, we use the exact match based on the generated index name
                // rather than selecting the optimal one
                // in order to handle that, we count the number of select many that would happen because of the query
                // and match it to the number of select many in the index
                if (abstractViewGenerator.CountOfSelectMany != distinctSelectManyFields.Count)
                {
                    explain(indexName,
                            () => "Can't choose an index with a different number of from clauses / SelectMany, will affect queries like Count().");
                    return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                }

                if (normalizedFieldsQueriedUpon.All(abstractViewGenerator.ContainsFieldOnMap) == false)
                {
                    explain(indexName, () =>
                    {
                        var missingFields =
                            normalizedFieldsQueriedUpon.Where(s => abstractViewGenerator.ContainsFieldOnMap(s) == false);
                        return("The following fields are missing: " + string.Join(", ", missingFields));
                    });
                    currentBestState = DynamicQueryMatchType.Partial;
                }

                var indexDefinition = database.IndexDefinitionStorage.GetIndexDefinition(indexName);
                if (indexDefinition == null)
                {
                    return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                }

                if (indexQuery.HighlightedFields != null && indexQuery.HighlightedFields.Length > 0)
                {
                    var nonHighlightableFields = indexQuery
                                                 .HighlightedFields
                                                 .Where(x =>
                                                        !indexDefinition.Stores.ContainsKey(x.Field) ||
                                                        indexDefinition.Stores[x.Field] != FieldStorage.Yes ||
                                                        !indexDefinition.Indexes.ContainsKey(x.Field) ||
                                                        indexDefinition.Indexes[x.Field] != FieldIndexing.Analyzed ||
                                                        !indexDefinition.TermVectors.ContainsKey(x.Field) ||
                                                        indexDefinition.TermVectors[x.Field] != FieldTermVector.WithPositionsAndOffsets)
                                                 .Select(x => x.Field)
                                                 .ToArray();

                    if (nonHighlightableFields.Any())
                    {
                        explain(indexName,
                                () => "The following fields could not be highlighted because they are not stored, analyzed and using term vectors with positions and offsets: " +
                                string.Join(", ", nonHighlightableFields));
                        return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                    }
                }

                if (indexQuery.SortedFields != null && indexQuery.SortedFields.Length > 0)
                {
                    var sortInfo = DynamicQueryMapping.GetSortInfo(s => { });

                    foreach (var sortedField in indexQuery.SortedFields)                                     // with matching sort options
                    {
                        var normalizedFieldName = DynamicQueryMapping.ReplaceInvalidCharactersForFields(sortedField.Field);
                        if (normalizedFieldName.StartsWith(Constants.RandomFieldName))
                        {
                            return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                        }

                        // if the field is not in the output, then we can't sort on it.
                        if (abstractViewGenerator.ContainsField(normalizedFieldName) == false)
                        {
                            explain(indexName,
                                    () =>
                                    "Rejected because index does not contains field '" + normalizedFieldName + "' which we need to sort on");
                            currentBestState = DynamicQueryMatchType.Partial;
                            continue;
                        }

                        var dynamicSortInfo = sortInfo.FirstOrDefault(x => x.Field == normalizedFieldName);

                        if (dynamicSortInfo == null)                                        // no sort order specified, we don't care, probably
                        {
                            continue;
                        }

                        SortOptions value;
                        if (indexDefinition.SortOptions.TryGetValue(normalizedFieldName, out value) == false)
                        {
                            switch (dynamicSortInfo.FieldType)                                            // if we can't find the value, we check if we asked for the default sorting
                            {
                            case SortOptions.String:
                            case SortOptions.None:
                                continue;

                            default:
                                explain(indexName,
                                        () => "The specified sort type is different than the default for field: " + normalizedFieldName);
                                return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                            }
                        }

                        if (value != dynamicSortInfo.FieldType)
                        {
                            explain(indexName,
                                    () =>
                                    "The specified sort type (" + dynamicSortInfo.FieldType + ") is different than the one specified for field '" +
                                    normalizedFieldName + "' (" + value + ")");
                            return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                        }
                    }
                }

                if (indexDefinition.Analyzers != null && indexDefinition.Analyzers.Count > 0)
                {
                    // none of the fields have custom analyzers
                    if (normalizedFieldsQueriedUpon.Any(indexDefinition.Analyzers.ContainsKey))
                    {
                        explain(indexName, () =>
                        {
                            var fields = normalizedFieldsQueriedUpon.Where(indexDefinition.Analyzers.ContainsKey);
                            return("The following field have a custom analyzer: " + string.Join(", ", fields));
                        });
                        return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                    }
                }

                if (indexDefinition.Indexes != null && indexDefinition.Indexes.Count > 0)
                {
                    //If any of the fields we want to query on are set to something other than the default, don't use the index
                    var anyFieldWithNonDefaultIndexing = normalizedFieldsQueriedUpon.Where(x =>
                    {
                        FieldIndexing analyzedInfo;
                        if (indexDefinition.Indexes.TryGetValue(x, out analyzedInfo))
                        {
                            if (analyzedInfo != FieldIndexing.Default)
                            {
                                return(true);
                            }
                        }
                        return(false);
                    });

                    if (anyFieldWithNonDefaultIndexing.Any())
                    {
                        explain(indexName, () =>
                        {
                            var fields = anyFieldWithNonDefaultIndexing.Where(indexDefinition.Analyzers.ContainsKey);
                            return("The following field have aren't using default indexing: " + string.Join(", ", fields));
                        });
                        return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                    }
                }
                if (currentBestState != DynamicQueryMatchType.Complete && indexDefinition.Type != "Auto")
                {
                    return(new DynamicQueryOptimizerResult(indexName, DynamicQueryMatchType.Failure));
                }
                return(new DynamicQueryOptimizerResult(indexName, currentBestState));
            })
                          .Where(result => result.MatchType != DynamicQueryMatchType.Failure)
                          .GroupBy(x => x.MatchType)
                          .ToDictionary(x => x.Key, x => x.ToArray());


            DynamicQueryOptimizerResult[] optimizerResults;
            if (results.TryGetValue(DynamicQueryMatchType.Complete, out optimizerResults) && optimizerResults.Length > 0)
            {
                DynamicQueryOptimizerResult[] prioritizedResults = null;
                database.TransactionalStorage.Batch(accessor =>
                {
                    prioritizedResults = optimizerResults.OrderByDescending(result =>
                    {
                        var stats = accessor.Indexing.GetIndexStats(result.IndexName);
                        if (stats == null)
                        {
                            return(Etag.Empty);
                        }

                        return(stats.LastIndexedEtag);
                    })
                                         .ThenByDescending(result =>
                    {
                        var abstractViewGenerator =
                            database.IndexDefinitionStorage.GetViewGenerator(
                                result.IndexName);
                        if (abstractViewGenerator == null)
                        {
                            return(-1);
                        }
                        return(abstractViewGenerator.CountOfFields);
                    })
                                         .ToArray();
                });
                for (int i = 1; i < prioritizedResults.Length; i++)
                {
                    explain(prioritizedResults[i].IndexName,
                            () => "Wasn't the widest / most unstable index matching this query");
                }

                return(prioritizedResults[0]);
            }

            if (results.TryGetValue(DynamicQueryMatchType.Partial, out optimizerResults) && optimizerResults.Length > 0)
            {
                return(optimizerResults.OrderByDescending(x =>
                {
                    var viewGenerator = database.IndexDefinitionStorage.GetViewGenerator(x.IndexName);
                    if (viewGenerator == null)
                    {
                        return -1;
                    }
                    return viewGenerator.CountOfFields;
                }).First());
            }

            return(new DynamicQueryOptimizerResult("<invalid index>", DynamicQueryMatchType.Failure));
        }
示例#2
0
        public string SelectAppropriateIndex(string entityName, IndexQuery indexQuery)
        {
            // There isn't much point for query optimizer of aggregation indexes
            // the main reason is that we must always aggregate on the same items, and using the same
            // aggregation. Therefore we can't reuse one aggregate index for another query.
            // We decline to suggest an index here and choose to use the default index created for this
            // sort of query, which is what we would have to choose anyway.
            if (indexQuery.AggregationOperation != AggregationOperation.None)
            {
                return(null);
            }

            var fieldsQueriedUpon = SimpleQueryParser.GetFieldsForDynamicQuery(indexQuery.Query).Select(x => x.Item2);

            return(database.IndexDefinitionStorage.IndexNames
                   .Where(indexName =>
            {
                var abstractViewGenerator = database.IndexDefinitionStorage.GetViewGenerator(indexName);
                if (abstractViewGenerator == null)                                 // there is no matching view generator
                {
                    return false;
                }

                if (abstractViewGenerator.ReduceDefinition != null)                                 // we can't choose a map/reduce index
                {
                    return false;
                }

                if (abstractViewGenerator.TransformResultsDefinition != null)                                // we can't choose an index with transform results
                {
                    return false;
                }

                if (abstractViewGenerator.HasWhereClause)                                 // without a where clause
                {
                    return false;
                }

                // we can't select an index that has SelectMany in it, because it result in invalid results when
                // you query it for things like Count, see https://github.com/ravendb/ravendb/issues/250
                // for indexes with internal projections, we use the exact match based on the generated index name
                // rather than selecting the optimal one
                if (abstractViewGenerator.CountOfSelectMany > 1)
                {
                    return false;
                }

                if (abstractViewGenerator.ForEntityName != entityName)                                 // for the specified entity name
                {
                    return false;
                }

                return fieldsQueriedUpon.All(abstractViewGenerator.ContainsFieldOnMap);
            })
                   .Where(indexName =>
            {
                var indexDefinition = database.IndexDefinitionStorage.GetIndexDefinition(indexName);
                if (indexDefinition == null)
                {
                    return false;
                }
                var abstractViewGenerator = database.IndexDefinitionStorage.GetViewGenerator(indexName);
                if (abstractViewGenerator == null)
                {
                    return false;
                }

                if (indexQuery.SortedFields != null)
                {
                    var sortInfo = DynamicQueryMapping.GetSortInfo(s => { });

                    foreach (var sortedField in indexQuery.SortedFields)                                     // with matching sort options
                    {
                        // if the field is not in the output, then we can't sort on it.
                        if (abstractViewGenerator.ContainsField(sortedField.Field) == false)
                        {
                            return false;
                        }

                        var dynamicSortInfo = sortInfo.FirstOrDefault(x => x.Field == sortedField.Field);

                        if (dynamicSortInfo == null)                                        // no sort order specified, we don't care, probably
                        {
                            continue;
                        }

                        SortOptions value;
                        if (indexDefinition.SortOptions.TryGetValue(sortedField.Field, out value) == false)
                        {
                            switch (dynamicSortInfo.FieldType)                                            // if we can't find the value, we check if we asked for the default sorting
                            {
                            case SortOptions.String:
                            case SortOptions.None:
                                continue;

                            default:
                                return false;
                            }
                        }

                        if (value != dynamicSortInfo.FieldType)
                        {
                            return false;                                             // different sort order, there is a problem here
                        }
                    }
                }

                if (indexDefinition.Analyzers != null)
                {
                    // none of the fields have custom analyzers
                    if (fieldsQueriedUpon.Any(indexDefinition.Analyzers.ContainsKey))
                    {
                        return false;
                    }
                }

                return true;
            })
                   .OrderByDescending(indexName =>
            {
                // We select the widest index, because we want to encourage bigger indexes
                // Over time, it means that we smaller indexes would wither away and die, while
                // bigger indexes will be selected more often and then upgrade to permanent indexes
                var abstractViewGenerator = database.IndexDefinitionStorage.GetViewGenerator(indexName);
                if (abstractViewGenerator == null)                                 // there is a matching view generator
                {
                    return -1;
                }
                return abstractViewGenerator.CountOfFields;
            })
                   .FirstOrDefault());
        }
示例#3
0
        public string SelectAppropriateIndex(string entityName, IndexQuery indexQuery)
        {
            // There isn't much point for query optimizer of aggregation indexes
            // the main reason is that we must always aggregate on the same items, and using the same
            // aggregation. Therefore we can't reuse one aggregate index for another query.
            // We decline to suggest an index here and choose to use the default index created for this
            // sort of query, which is what we would have to choose anyway.
            if (indexQuery.AggregationOperation != AggregationOperation.None)
            {
                return(null);
            }

            if (string.IsNullOrEmpty(indexQuery.Query) &&                                   // we optimize for empty queries to use Raven/DocumentsByEntityName
                (indexQuery.SortedFields == null || indexQuery.SortedFields.Length == 0) && // and no sorting was requested
                database.IndexDefinitionStorage.Contains("Raven/DocumentsByEntityName"))    // and Raven/DocumentsByEntityName exists
            {
                if (string.IsNullOrEmpty(entityName) == false)
                {
                    indexQuery.Query = "Tag:" + entityName;
                }
                return("Raven/DocumentsByEntityName");
            }

            var fieldsQueriedUpon           = SimpleQueryParser.GetFieldsForDynamicQuery(indexQuery.Query).Select(x => x.Item2).ToArray();
            var normalizedFieldsQueriedUpon =
                fieldsQueriedUpon.Select(DynamicQueryMapping.ReplaceIndavlidCharactersForFields).ToArray();
            var distinctSelectManyFields = new HashSet <string>();

            foreach (var field in fieldsQueriedUpon)
            {
                var parts = field.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
                for (int i = 1; i < parts.Length; i++)
                {
                    distinctSelectManyFields.Add(string.Join(",", parts.Take(i)));
                }
            }

            return(database.IndexDefinitionStorage.IndexNames
                   .Where(indexName =>
            {
                var abstractViewGenerator = database.IndexDefinitionStorage.GetViewGenerator(indexName);
                if (abstractViewGenerator == null)                                 // there is no matching view generator
                {
                    return false;
                }

                if (abstractViewGenerator.ReduceDefinition != null)                                 // we can't choose a map/reduce index
                {
                    return false;
                }

                if (abstractViewGenerator.TransformResultsDefinition != null)                                // we can't choose an index with transform results
                {
                    return false;
                }

                if (abstractViewGenerator.HasWhereClause)                                 // without a where clause
                {
                    return false;
                }

                // we can't select an index that has SelectMany in it, because it result in invalid results when
                // you query it for things like Count, see https://github.com/ravendb/ravendb/issues/250
                // for indexes with internal projections, we use the exact match based on the generated index name
                // rather than selecting the optimal one
                // in order to handle that, we count the number of select many that would happen because of the query
                // and match it to the number of select many in the index
                if (abstractViewGenerator.CountOfSelectMany != distinctSelectManyFields.Count)
                {
                    return false;
                }

                if (entityName == null)
                {
                    if (abstractViewGenerator.ForEntityNames.Count != 0)
                    {
                        return false;
                    }
                }
                else
                {
                    if (abstractViewGenerator.ForEntityNames.Count != 1 ||                                     // we only allow indexes with a single entity name
                        abstractViewGenerator.ForEntityNames.Contains(entityName) == false)                    // for the specified entity name
                    {
                        return false;
                    }
                }

                if (normalizedFieldsQueriedUpon.All(abstractViewGenerator.ContainsFieldOnMap) == false)
                {
                    return false;
                }

                var indexDefinition = database.IndexDefinitionStorage.GetIndexDefinition(indexName);
                if (indexDefinition == null)
                {
                    return false;
                }

                if (indexQuery.SortedFields != null && indexQuery.SortedFields.Length > 0)
                {
                    var sortInfo = DynamicQueryMapping.GetSortInfo(s => { });

                    foreach (var sortedField in indexQuery.SortedFields)                                     // with matching sort options
                    {
                        if (sortedField.Field.StartsWith(Constants.RandomFieldName))
                        {
                            continue;
                        }

                        // if the field is not in the output, then we can't sort on it.
                        if (abstractViewGenerator.ContainsField(sortedField.Field) == false)
                        {
                            return false;
                        }

                        var dynamicSortInfo = sortInfo.FirstOrDefault(x => x.Field == sortedField.Field);

                        if (dynamicSortInfo == null)                                        // no sort order specified, we don't care, probably
                        {
                            continue;
                        }

                        SortOptions value;
                        if (indexDefinition.SortOptions.TryGetValue(sortedField.Field, out value) == false)
                        {
                            switch (dynamicSortInfo.FieldType)                                            // if we can't find the value, we check if we asked for the default sorting
                            {
                            case SortOptions.String:
                            case SortOptions.None:
                                continue;

                            default:
                                return false;
                            }
                        }

                        if (value != dynamicSortInfo.FieldType)
                        {
                            return false;                                             // different sort order, there is a problem here
                        }
                    }
                }

                if (indexDefinition.Analyzers != null && indexDefinition.Analyzers.Count > 0)
                {
                    // none of the fields have custom analyzers
                    if (normalizedFieldsQueriedUpon.Any(indexDefinition.Analyzers.ContainsKey))
                    {
                        return false;
                    }
                }

                return true;
            })
                   .OrderByDescending(indexName =>
            {
                // We select the widest index, because we want to encourage bigger indexes
                // Over time, it means that we smaller indexes would wither away and die, while
                // bigger indexes will be selected more often and then upgrade to permanent indexes
                var abstractViewGenerator = database.IndexDefinitionStorage.GetViewGenerator(indexName);
                if (abstractViewGenerator == null)                                 // there is a matching view generator
                {
                    return -1;
                }
                return abstractViewGenerator.CountOfFields;
            })
                   .FirstOrDefault());
        }
示例#4
0
        public string SelectAppropriateIndex(
            string entityName,
            IndexQuery indexQuery,
            List <Explanation> explanations = null)
        {
            // There isn't much point for query optimizer of aggregation indexes
            // the main reason is that we must always aggregate on the same items, and using the same
            // aggregation. Therefore we can't reuse one aggregate index for another query.
            // We decline to suggest an index here and choose to use the default index created for this
            // sort of query, which is what we would have to choose anyway.
            if (indexQuery.AggregationOperation != AggregationOperation.None)
            {
                return(null);
            }

            if (string.IsNullOrEmpty(indexQuery.Query) &&                                   // we optimize for empty queries to use Raven/DocumentsByEntityName
                (indexQuery.SortedFields == null || indexQuery.SortedFields.Length == 0) && // and no sorting was requested
                database.IndexDefinitionStorage.Contains("Raven/DocumentsByEntityName"))    // and Raven/DocumentsByEntityName exists
            {
                if (string.IsNullOrEmpty(entityName) == false)
                {
                    indexQuery.Query = "Tag:" + entityName;
                }
                return("Raven/DocumentsByEntityName");
            }

            var fieldsQueriedUpon           = SimpleQueryParser.GetFieldsForDynamicQuery(indexQuery).Select(x => x.Item2).ToArray();
            var normalizedFieldsQueriedUpon =
                fieldsQueriedUpon.Select(DynamicQueryMapping.ReplaceIndavlidCharactersForFields).ToArray();
            var distinctSelectManyFields = new HashSet <string>();

            foreach (var field in fieldsQueriedUpon)
            {
                var parts = field.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
                for (int i = 1; i < parts.Length; i++)
                {
                    distinctSelectManyFields.Add(string.Join(",", parts.Take(i)));
                }
            }

            ExplainDelegate explain = (index, rejectionReason) => { };

            if (explanations != null)
            {
                explain = (index, rejectionReason) => explanations.Add(new Explanation
                {
                    Index  = index,
                    Reason = rejectionReason()
                });
            }


            // there is no reason why we can't use indexes with transform results
            // we merely need to disable the transform results for this particular query
            indexQuery.SkipTransformResults = true;
            var results = database.IndexDefinitionStorage.IndexNames
                          .Where(indexName =>
            {
                var abstractViewGenerator = database.IndexDefinitionStorage.GetViewGenerator(indexName);
                if (abstractViewGenerator == null)                                 // there is no matching view generator
                {
                    explain(indexName, () => "There is no matching view generator. Maybe the index in the process of being deleted?");
                    return(false);
                }

                if (entityName == null)
                {
                    if (abstractViewGenerator.ForEntityNames.Count != 0)
                    {
                        explain(indexName, () => "Query is not specific for entity name, but the index filter by entity names.");
                        return(false);
                    }
                }
                else
                {
                    if (abstractViewGenerator.ForEntityNames.Count > 1)                                     // we only allow indexes with a single entity name
                    {
                        explain(indexName, () => "Index contains more than a single entity name, may result in a different type being returned.");
                        return(false);
                    }
                    if (abstractViewGenerator.ForEntityNames.Count == 0)
                    {
                        explain(indexName, () => "Query is specific for entity name, but the index searches across all of them, may result in a different type being returned.");
                        return(false);
                    }
                    if (abstractViewGenerator.ForEntityNames.Contains(entityName) == false)                                     // for the specified entity name
                    {
                        explain(indexName, () => string.Format("Index does not apply to entity name: {0}", entityName));
                        return(false);
                    }
                }

                if (abstractViewGenerator.ReduceDefinition != null)                                 // we can't choose a map/reduce index
                {
                    explain(indexName, () => "Can't choose a map/reduce index for dynamic queries.");
                    return(false);
                }

                if (abstractViewGenerator.HasWhereClause)                                 // without a where clause
                {
                    explain(indexName, () => "Can't choose an index with a where clause, it might filter things that the query is looking for.");
                    return(false);
                }

                // we can't select an index that has SelectMany in it, because it result in invalid results when
                // you query it for things like Count, see https://github.com/ravendb/ravendb/issues/250
                // for indexes with internal projections, we use the exact match based on the generated index name
                // rather than selecting the optimal one
                // in order to handle that, we count the number of select many that would happen because of the query
                // and match it to the number of select many in the index
                if (abstractViewGenerator.CountOfSelectMany != distinctSelectManyFields.Count)
                {
                    explain(indexName,
                            () => "Can't choose an index with a different number of from clauses / SelectMany, will affect queries like Count().");
                    return(false);
                }

                if (normalizedFieldsQueriedUpon.All(abstractViewGenerator.ContainsFieldOnMap) == false)
                {
                    explain(indexName, () =>
                    {
                        var missingFields =
                            normalizedFieldsQueriedUpon.Where(s => abstractViewGenerator.ContainsFieldOnMap(s) == false);
                        return("The following fields are missing: " + string.Join(", ", missingFields));
                    });
                    return(false);
                }

                var indexDefinition = database.IndexDefinitionStorage.GetIndexDefinition(indexName);
                if (indexDefinition == null)
                {
                    return(false);
                }

                if (indexQuery.SortedFields != null && indexQuery.SortedFields.Length > 0)
                {
                    var sortInfo = DynamicQueryMapping.GetSortInfo(s => { });

                    foreach (var sortedField in indexQuery.SortedFields)                                     // with matching sort options
                    {
                        if (sortedField.Field.StartsWith(Constants.RandomFieldName))
                        {
                            continue;
                        }

                        // if the field is not in the output, then we can't sort on it.
                        if (abstractViewGenerator.ContainsField(sortedField.Field) == false)
                        {
                            explain(indexName,
                                    () =>
                                    "Rejected because index does not contains field '" + sortedField.Field + "' which we need to sort on");
                            return(false);
                        }

                        var dynamicSortInfo = sortInfo.FirstOrDefault(x => x.Field == sortedField.Field);

                        if (dynamicSortInfo == null)                                        // no sort order specified, we don't care, probably
                        {
                            continue;
                        }

                        SortOptions value;
                        if (indexDefinition.SortOptions.TryGetValue(sortedField.Field, out value) == false)
                        {
                            switch (dynamicSortInfo.FieldType)                                            // if we can't find the value, we check if we asked for the default sorting
                            {
                            case SortOptions.String:
                            case SortOptions.None:
                                continue;

                            default:
                                explain(indexName,
                                        () => "The specified sort type is different than the default for field: " + sortedField.Field);
                                return(false);
                            }
                        }

                        if (value != dynamicSortInfo.FieldType)
                        {
                            explain(indexName,
                                    () =>
                                    "The specified sort type (" + dynamicSortInfo.FieldType + ") is different than the one specified for field '" +
                                    sortedField.Field + "' (" + value + ")");
                            return(false);                                            // different sort order, there is a problem here
                        }
                    }
                }

                if (indexDefinition.Analyzers != null && indexDefinition.Analyzers.Count > 0)
                {
                    // none of the fields have custom analyzers
                    if (normalizedFieldsQueriedUpon.Any(indexDefinition.Analyzers.ContainsKey))
                    {
                        explain(indexName, () =>
                        {
                            var fields = normalizedFieldsQueriedUpon.Where(indexDefinition.Analyzers.ContainsKey);
                            return("The following field have a custom analyzer: " + string.Join(", ", fields));
                        });
                        return(false);
                    }
                }

                if (indexDefinition.Indexes != null && indexDefinition.Indexes.Count > 0)
                {
                    //If any of the fields we want to query on are set to something other than the default, don't use the index
                    var anyFieldWithNonDefaultIndexing = normalizedFieldsQueriedUpon.Where(x =>
                    {
                        FieldIndexing analysedInfo;
                        if (indexDefinition.Indexes.TryGetValue(x, out analysedInfo))
                        {
                            if (analysedInfo != FieldIndexing.Default)
                            {
                                return(true);
                            }
                        }
                        return(false);
                    });

                    if (anyFieldWithNonDefaultIndexing.Any())
                    {
                        explain(indexName, () =>
                        {
                            var fields = anyFieldWithNonDefaultIndexing.Where(indexDefinition.Analyzers.ContainsKey);
                            return("The following field have aren't using default indexing: " + string.Join(", ", fields));
                        });
                        return(false);
                    }
                }
                return(true);
            })
                          .OrderByDescending(indexName =>
            {
                // We select the widest index, because we want to encourage bigger indexes
                // Over time, it means that we smaller indexes would wither away and die, while
                // bigger indexes will be selected more often and then upgrade to permanent indexes
                var abstractViewGenerator = database.IndexDefinitionStorage.GetViewGenerator(indexName);
                if (abstractViewGenerator == null)                                 // there isn't a matching view generator
                {
                    return(-1);
                }
                return(abstractViewGenerator.CountOfFields);
            });

            string name = null;

            foreach (var indexName in results)
            {
                if (name == null)
                {
                    name = indexName;
                }
                else
                {
                    explain(indexName, () => "Wasn't the widest index matching this query.");
                }
            }

            explain(name ?? "Temporary index will be created", () => "Selected as best match");

            return(name);
        }