public static string GetQuery <TEntity>(AggregateExecutionModel model)
{
var entityDefinition = EntityMapping.GetOrCreateDefinition(typeof(TEntity));
var stages = string.Join(", ", model.Stages.Select(x => x.ToString()));
return($"db.{entityDefinition.CollectionName}.aggregate([{stages}])");
}
private AggregateExecutionModel GetExecutionModel(Expression expression, bool isAsync = false)
{
//Use the official driver to do the heavy lifting on the query translation
var underlyingProvider = GetCollection().AsQueryable().Provider;
var providerType = underlyingProvider.GetType(); //Type: MongoQueryProviderImpl (internal)
var translatedQuery = providerType.GetMethod("Translate", BindingFlags.NonPublic | BindingFlags.Instance)
.Invoke(underlyingProvider, new[] { expression }); //Type: QueryableTranslation (internal)
var translatedQueryType = translatedQuery.GetType();
//We can't cast to AggregateQueryableExecutionModel<T> directly as we don't have generic parameter T
//While it may be TEntity, it could also be something else
var underlyingExecutionModel = translatedQueryType.GetProperty("Model").GetValue(translatedQuery) as QueryableExecutionModel;
var modelType = underlyingExecutionModel.GetType(); //Assumed type: AggregateQueryableExecutionModel<T>
//Retrieve the stages from reflection
var expressionStages = modelType.GetProperty(nameof(AggregateQueryableExecutionModel <object> .Stages))
.GetValue(underlyingExecutionModel) as IEnumerable <BsonDocument>;
//Retreve the serializer from reflection
var serializer = modelType.GetProperty(nameof(AggregateQueryableExecutionModel <object> .OutputSerializer))
.GetValue(underlyingExecutionModel) as IBsonSerializer;
if (PreStage != null)
{
expressionStages = new[] { PreStage }.Concat(expressionStages);
}
var result = new AggregateExecutionModel
{
Stages = expressionStages,
Serializer = serializer
};
//Get the result transforming lambda (allows things like FirstOrDefault, Count, Average etc to work properly)
var resultTransformer = translatedQueryType.GetProperty("ResultTransformer").GetValue(translatedQuery); //Type: Mixed (implements IResultTransformer (internal))
if (resultTransformer != null)
{
result.ResultTransformer = ResultTransformers.Transform(expression, serializer.ValueType, isAsync) as LambdaExpression;
//Note: In the future this can change from the initial reflection to a `TryTransform` function where it checks the expression itself
// The reason we are doing this method first is to weed out the bugs and any core missing functionality.
}
return(result);
}
private async IAsyncEnumerable <TResult> ExecuteModelAsync <TResult>(AggregateExecutionModel model, [EnumeratorCancellation] CancellationToken cancellationToken)
{
var serializer = model.Serializer as IBsonSerializer <TResult>;
var pipeline = PipelineDefinition <TEntity, TResult> .Create(model.Stages, serializer);
using (var diagnostics = DiagnosticRunner.Start <TEntity>(Connection, model))
{
IAsyncCursor <TResult> underlyingCursor;
try
{
underlyingCursor = await GetCollection().AggregateAsync(pipeline, cancellationToken: cancellationToken);
}
catch (Exception exception)
{
diagnostics.Error(exception);
throw;
}
var hasFirstResult = false;
while (await underlyingCursor.MoveNextAsync(cancellationToken))
{
if (!hasFirstResult)
{
hasFirstResult = true;
diagnostics.FirstReadResult <TResult>();
}
var resultBatch = underlyingCursor.Current;
foreach (var item in resultBatch)
{
if (item is TEntity entityItem &&
(model.ResultTransformer == null ||
model.ResultTransformer.ReturnType == typeof(ValueTask <TEntity>) ||
model.ResultTransformer.ReturnType == typeof(Task <TEntity>)))
{
EntityProcessors.ProcessEntity(entityItem, Connection);
}
yield return(item);
}
}
}
}
private IEnumerable <TResult> ExecuteModel <TResult>(AggregateExecutionModel model)
{
var serializer = model.Serializer as IBsonSerializer <TResult>;
var pipeline = PipelineDefinition <TEntity, TResult> .Create(model.Stages, serializer);
using (var diagnostics = DiagnosticRunner.Start <TEntity>(Connection, model))
{
IEnumerable <TResult> underlyingResult;
try
{
underlyingResult = GetCollection().Aggregate(pipeline).ToEnumerable();
}
catch (Exception exception)
{
diagnostics.Error(exception);
throw;
}
using (var enumerator = underlyingResult.GetEnumerator())
{
var hasFirstResult = false;
while (enumerator.MoveNext())
{
if (!hasFirstResult)
{
hasFirstResult = true;
diagnostics.FirstReadResult <TResult>();
}
var item = enumerator.Current;
if (item is TEntity entityItem)
{
EntityProcessors.ProcessEntity(entityItem, Connection);
}
yield return(item);
}
}
}
}
private AggregateExecutionModel GetExecutionModel(Expression expression)
{
var underlyingProvider = GetCollection().AsQueryable().Provider;
var providerType = underlyingProvider.GetType();
var translatedQuery = providerType.GetMethod("Translate", BindingFlags.NonPublic | BindingFlags.Instance)
.Invoke(underlyingProvider, new[] { expression });
var translatedQueryType = translatedQuery.GetType();
//Get the model stages and processing type
var underlyingExecutionModel = translatedQueryType.GetProperty("Model").GetValue(translatedQuery) as QueryableExecutionModel;
var modelType = underlyingExecutionModel.GetType(); //Assumed type: AggregateQueryableExecutionModel<>
var expressionStages = modelType.GetProperty(nameof(AggregateQueryableExecutionModel <object> .Stages))
.GetValue(underlyingExecutionModel) as IEnumerable <BsonDocument>;
var serializer = modelType.GetProperty(nameof(AggregateQueryableExecutionModel <object> .OutputSerializer))
.GetValue(underlyingExecutionModel) as IBsonSerializer;
if (PreStage != null)
{
expressionStages = new[] { PreStage }.Concat(expressionStages);
}
var result = new AggregateExecutionModel
{
Stages = expressionStages,
Serializer = serializer
};
//Get the result transforming lambda (allows things like FirstOrDefault, Count, Average etc to work properly)
var resultTransformer = translatedQueryType.GetProperty("ResultTransformer").GetValue(translatedQuery);
if (resultTransformer != null)
{
var resultTransformerType = resultTransformer.GetType();
var lambda = resultTransformerType.GetMethod("CreateAggregator").Invoke(resultTransformer, new[] { serializer.ValueType });
result.ResultTransformer = lambda as LambdaExpression;
}
return(result);
}
