private bool CanBeJoinCondition(Expression expression, HashSet <TableAlias> left, HashSet <TableAlias> right, HashSet <TableAlias> all)
{
var referenced = DbReferencedAliasGatherer.Gather(expression);
var leftOkay = referenced.Intersect(left).Any();
var rightOkay = referenced.Intersect(right).Any();
var subset = referenced.IsSubsetOf(all);
return(leftOkay && rightOkay && subset);
}
public static HashSet <TableAlias> Gather(Expression source)
{
var gatherer = new DbReferencedAliasGatherer();
if (gatherer != null)
{
gatherer.Visit(source);
}
return(gatherer.aliases);
}
private bool GetEquiJoinKeyExpressions(Expression predicate, TableAlias outerAlias, List <Expression> outerExpressions, List <Expression> innerExpressions)
{
if (predicate.NodeType == ExpressionType.Equal)
{
var b = predicate as BinaryExpression;
var leftCol = this.GetColumnExpression(b.Left);
var rightCol = this.GetColumnExpression(b.Right);
if (leftCol != null && rightCol != null)
{
if (leftCol.Alias == outerAlias)
{
outerExpressions.Add(b.Left);
innerExpressions.Add(b.Right);
return(true);
}
else if (rightCol.Alias == outerAlias)
{
innerExpressions.Add(b.Left);
outerExpressions.Add(b.Right);
return(true);
}
}
}
var hadKey = false;
var parts = predicate.Split(ExpressionType.And, ExpressionType.AndAlso);
if (parts.Length > 1)
{
foreach (var part in parts)
{
var hasOuterAliasReference = DbReferencedAliasGatherer.Gather(part).Contains(outerAlias);
if (hasOuterAliasReference)
{
if (GetEquiJoinKeyExpressions(part, outerAlias, outerExpressions, innerExpressions) == false)
{
return(false);
}
hadKey = true;
}
}
}
return(hadKey);
}
protected override Expression VisitJoin(DbJoinExpression join)
{
join = base.VisitJoin(join) as DbJoinExpression;
if (join.JoinType == JoinType.CrossApply || join.JoinType == JoinType.OuterApply)
{
if (join.Right is DbTableExpression)
{
return(new DbJoinExpression(JoinType.CrossJoin, join.Left, join.Right, null));
}
if (join.Right is DbSelectExpression select && select.Take == null && select.Skip == null && !DbAggregateChecker.HasAggregates(select) && (select.GroupBy == null || select.GroupBy.Count == 0))
{
var selectWithoutWhere = select.SetWhere(null);
var referencedAliases = DbReferencedAliasGatherer.Gather(selectWithoutWhere);
var declaredAliases = DbDeclaredAliasGatherer.Gather(join.Left);
if (referencedAliases != null)
{
referencedAliases.IntersectWith(declaredAliases);
}
if (referencedAliases.Count == 0)
{
var where = select.Where;
select = selectWithoutWhere;
var pc = DbColumnProjector.ProjectColumns(this.language, where, select.Columns, select.Alias, DbDeclaredAliasGatherer.Gather(select.From));
select = select.SetColumns(pc.Columns);
where = pc.Projector;
var jt = (where == null) ? JoinType.CrossJoin : (join.JoinType == JoinType.CrossApply ? JoinType.InnerJoin : JoinType.LeftOuter);
return(new DbJoinExpression(jt, join.Left, select, where));
}
}
}
return(join);
}