protected override IEnumerable <Entity> ExecuteInternal(IDictionary <string, DataSource> dataSources, IQueryExecutionOptions options, IDictionary <string, Type> parameterTypes, IDictionary <string, object> parameterValues)
{
// https://sqlserverfast.com/epr/merge-join/
// Implemented inner, left outer, right outer and full outer variants
// Not implemented semi joins
// TODO: Handle many-to-many joins
// TODO: Handle union & concatenate
// Left & Right: GetNext, mark as unmatched
var leftSchema = LeftSource.GetSchema(dataSources, parameterTypes);
var rightSchema = RightSource.GetSchema(dataSources, parameterTypes);
var left = LeftSource.Execute(dataSources, options, parameterTypes, parameterValues).GetEnumerator();
var right = RightSource.Execute(dataSources, options, parameterTypes, parameterValues).GetEnumerator();
var mergedSchema = GetSchema(dataSources, parameterTypes, true);
var additionalJoinCriteria = AdditionalJoinCriteria?.Compile(mergedSchema, parameterTypes);
var hasLeft = left.MoveNext();
var hasRight = right.MoveNext();
var leftMatched = false;
var rightMatched = false;
var lt = new BooleanComparisonExpression
{
FirstExpression = LeftAttribute,
ComparisonType = BooleanComparisonType.LessThan,
SecondExpression = RightAttribute
}.Compile(mergedSchema, parameterTypes);
var eq = new BooleanComparisonExpression
{
FirstExpression = LeftAttribute,
ComparisonType = BooleanComparisonType.Equals,
SecondExpression = RightAttribute
}.Compile(mergedSchema, parameterTypes);
var gt = new BooleanComparisonExpression
{
FirstExpression = LeftAttribute,
ComparisonType = BooleanComparisonType.GreaterThan,
SecondExpression = RightAttribute
}.Compile(mergedSchema, parameterTypes);
while (!Done(hasLeft, hasRight))
{
// Compare key values
var merged = Merge(hasLeft ? left.Current : null, leftSchema, hasRight ? right.Current : null, rightSchema);
var isLt = lt(merged, parameterValues, options);
var isEq = eq(merged, parameterValues, options);
var isGt = gt(merged, parameterValues, options);
if (isLt || (hasLeft && !hasRight))
{
if (!leftMatched && (JoinType == QualifiedJoinType.LeftOuter || JoinType == QualifiedJoinType.FullOuter))
{
yield return(Merge(left.Current, leftSchema, null, rightSchema));
}
hasLeft = left.MoveNext();
leftMatched = false;
}
else if (isEq)
{
if ((!leftMatched || !SemiJoin) && (additionalJoinCriteria == null || additionalJoinCriteria(merged, parameterValues, options) == true))
{
yield return(merged);
}
leftMatched = true;
hasRight = right.MoveNext();
rightMatched = false;
}
else if (hasRight)
{
if (!rightMatched && (JoinType == QualifiedJoinType.RightOuter || JoinType == QualifiedJoinType.FullOuter))
{
yield return(Merge(null, leftSchema, right.Current, rightSchema));
}
hasRight = right.MoveNext();
rightMatched = false;
}
}
}
protected override IEnumerable <Entity> ExecuteInternal(IDictionary <string, DataSource> dataSources, IQueryExecutionOptions options, IDictionary <string, Type> parameterTypes, IDictionary <string, object> parameterValues)
{
_hashTable = new Dictionary <object, List <OuterRecord> >();
var mergedSchema = GetSchema(dataSources, parameterTypes, true);
var additionalJoinCriteria = AdditionalJoinCriteria?.Compile(mergedSchema, parameterTypes);
// Build the hash table
var leftSchema = LeftSource.GetSchema(dataSources, parameterTypes);
leftSchema.ContainsColumn(LeftAttribute.GetColumnName(), out var leftCol);
foreach (var entity in LeftSource.Execute(dataSources, options, parameterTypes, parameterValues))
{
var key = entity[leftCol];
if (!_hashTable.TryGetValue(key, out var list))
{
list = new List <OuterRecord>();
_hashTable[key] = list;
}
list.Add(new OuterRecord {
Entity = entity
});
}
// Probe the hash table using the right source
var rightSchema = RightSource.GetSchema(dataSources, parameterTypes);
rightSchema.ContainsColumn(RightAttribute.GetColumnName(), out var rightCol);
foreach (var entity in RightSource.Execute(dataSources, options, parameterTypes, parameterValues))
{
var key = entity[rightCol];
var matched = false;
if (_hashTable.TryGetValue(key, out var list))
{
foreach (var left in list)
{
if (SemiJoin && left.Used)
{
continue;
}
var merged = Merge(left.Entity, leftSchema, entity, rightSchema);
if (additionalJoinCriteria == null || additionalJoinCriteria(merged, parameterValues, options))
{
yield return(merged);
left.Used = true;
matched = true;
}
}
}
if (!matched && (JoinType == QualifiedJoinType.RightOuter || JoinType == QualifiedJoinType.FullOuter))
{
yield return(Merge(null, leftSchema, entity, rightSchema));
}
}
if (JoinType == QualifiedJoinType.LeftOuter || JoinType == QualifiedJoinType.FullOuter)
{
foreach (var unmatched in _hashTable.SelectMany(kvp => kvp.Value).Where(e => !e.Used))
{
yield return(Merge(unmatched.Entity, leftSchema, null, rightSchema));
}
}
}
