public static HashSet <ColumnExpression> Gather(HashSet <TableAlias> aliases, SelectExpression select)
{
var gatherer = new JoinColumnGatherer(aliases);
gatherer.Gather(select.Where);
return(gatherer.columns);
}
protected override Expression VisitProjection(ProjectionExpression proj)
{
SelectExpression save = currentSelect;
currentSelect = proj.Select;
try {
if (!isTopLevel)
{
if (CanJoinOnClient(currentSelect))
{
// make a query that combines all the constraints from the outer queries into a single select
var newOuterSelect = (SelectExpression)QueryDuplicator.Duplicate(save);
// remap any references to the outer select to the new alias;
var newInnerSelect = (SelectExpression)ColumnMapper.Map(proj.Select, newOuterSelect.Alias, save.Alias);
// add outer-join test
ProjectionExpression newInnerProjection = language.AddOuterJoinTest(new ProjectionExpression(newInnerSelect, proj.Projector));
newInnerSelect = newInnerProjection.Select;
Expression newProjector = newInnerProjection.Projector;
var newAlias = new TableAlias();
ProjectedColumns pc = ColumnProjector.ProjectColumns(language, newProjector, null, newAlias, newOuterSelect.Alias, newInnerSelect.Alias);
var join = new JoinExpression(JoinType.OuterApply, newOuterSelect, newInnerSelect, null);
var joinedSelect = new SelectExpression(newAlias, pc.Columns, join, null, null, null, proj.IsSingleton, null, null, false);
// apply client-join treatment recursively
currentSelect = joinedSelect;
newProjector = Visit(pc.Projector);
// compute keys (this only works if join condition was a single column comparison)
var outerKeys = new List <Expression>();
var innerKeys = new List <Expression>();
if (GetEquiJoinKeyExpressions(newInnerSelect.Where, newOuterSelect.Alias, outerKeys, innerKeys))
{
// outerKey needs to refer to the outer-scope's alias
IEnumerable <Expression> outerKey = outerKeys.Select(k => ColumnMapper.Map(k, save.Alias, newOuterSelect.Alias));
// innerKey needs to refer to the new alias for the select with the new join
IEnumerable <Expression> innerKey = innerKeys.Select(k => ColumnMapper.Map(k, joinedSelect.Alias, ((ColumnExpression)k).Alias));
var newProjection = new ProjectionExpression(joinedSelect, newProjector, proj.Aggregator);
return(new ClientJoinExpression(newProjection, outerKey, innerKey));
}
}
else
{
bool saveJoin = canJoinOnClient;
canJoinOnClient = false;
Expression result = base.VisitProjection(proj);
canJoinOnClient = saveJoin;
return(result);
}
}
else
{
isTopLevel = false;
}
return(base.VisitProjection(proj));
}
finally {
currentSelect = save;
}
}
protected override Expression VisitSelect(SelectExpression select)
{
selects.Add(select);
return(select); // don't visit sub-queries
}
private bool CanJoinOnClient(SelectExpression select)
{
// can add singleton (1:0,1) join if no grouping/aggregates or distinct
return(canJoinOnClient && currentMember != null && !policy.IsDeferLoaded(currentMember) && !select.IsDistinct && (select.GroupBy == null || select.GroupBy.Count == 0) &&
!AggregateChecker.HasAggregates(select));
}
protected override Expression VisitSelect(SelectExpression select)
{
aliases.Add(select.Alias);
return(select);
}
