private void MapAliases(Expression a, Expression b)
{
DbTableAlias[] prodA = DeclaredAliasGatherer.Gather(a).ToArray();
DbTableAlias[] prodB = DeclaredAliasGatherer.Gather(b).ToArray();
for (int i = 0, n = prodA.Length; i < n; i++)
{
_aliasScope.Add(prodA[i], prodB[i]);
}
}
protected override Expression VisitJoin(DbJoinExpression join)
{
join = (DbJoinExpression)base.VisitJoin(join);
if (join.Join == DbJoinType.CrossApply || join.Join == DbJoinType.OuterApply)
{
if (join.Right is DbTableExpression)
{
return(new DbJoinExpression(DbJoinType.CrossJoin, join.Left, join.Right, null));
}
else
{
DbSelectExpression select = join.Right as DbSelectExpression;
// Only consider rewriting cross apply if
// 1) right side is a select
// 2) other than in the where clause in the right-side select, no left-side declared aliases are referenced
// 3) and has no behavior that would change semantics if the where clause is removed (like groups, aggregates, take, skip, etc).
// Note: it is best to attempt this after redundant subqueries have been removed.
if (select != null &&
select.Take == null &&
select.Skip == null &&
!AggregateChecker.HasAggregates(select) &&
(select.GroupBy == null || select.GroupBy.Count == 0))
{
DbSelectExpression selectWithoutWhere = select.SetWhere(null);
HashSet <DbTableAlias> referencedAliases = ReferencedAliasGatherer.Gather(selectWithoutWhere);
HashSet <DbTableAlias> declaredAliases = DeclaredAliasGatherer.Gather(join.Left);
referencedAliases.IntersectWith(declaredAliases);
if (referencedAliases.Count == 0)
{
Expression where = select.Where;
select = selectWithoutWhere;
var pc = ColumnProjector.ProjectColumns(this.CanBeColumn, where, select.Columns, select.Alias, DeclaredAliasGatherer.Gather(select.From));
select = select.SetColumns(pc.Columns);
where = pc.Projector;
DbJoinType jt = (where == null) ? DbJoinType.CrossJoin :
(join.Join == DbJoinType.CrossApply ? DbJoinType.InnerJoin : DbJoinType.LeftOuter);
return(new DbJoinExpression(jt, join.Left, select, where));
}
}
}
}
return(join);
}
protected override Expression VisitJoin(DbJoinExpression join)
{
join = (DbJoinExpression)base.VisitJoin(join);
if (join.Join == DbJoinType.CrossJoin && this.currentWhere != null)
{
// try to figure out which parts of the current where expression can be used for a join condition
var declaredLeft = DeclaredAliasGatherer.Gather(join.Left);
var declaredRight = DeclaredAliasGatherer.Gather(join.Right);
var declared = new HashSet <DbTableAlias>(declaredLeft.Union(declaredRight));
var exprs = this.currentWhere.Split(ExpressionType.And, ExpressionType.AndAlso);
var good = exprs.Where(e => CanBeJoinCondition(e, declaredLeft, declaredRight, declared)).ToList();
if (good.Count > 0)
{
var condition = good.Join(ExpressionType.And);
join = this.UpdateJoin(join, DbJoinType.InnerJoin, join.Left, join.Right, condition);
var newWhere = exprs.Where(e => !good.Contains(e)).Join(ExpressionType.And);
this.currentWhere = newWhere;
}
}
return(join);
}
private Expression MakeSubquery(Expression expression)
{
var newAlias = new DbTableAlias();
var aliases = DeclaredAliasGatherer.Gather(expression);
var decls = new List <DbColumnDeclaration>();
foreach (var ta in aliases)
{
foreach (var col in this.columns[ta])
{
string name = decls.GetAvailableColumnName(col.Name);
var decl = new DbColumnDeclaration(name, col);
decls.Add(decl);
var newCol = new DbColumnExpression(col.Type, col.DbType, newAlias, col.Name);
this.map.Add(col, newCol);
}
}
return(new DbSelectExpression(newAlias, decls, expression, null));
}
public static HashSet<DbTableAlias> Gather(Expression source)
{
var gatherer = new DeclaredAliasGatherer();
gatherer.Visit(source);
return gatherer.aliases;
}
