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public static Gather ( |
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| source | ||
| return | HashSet |
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private void MapAliases(Expression a, Expression b)
{
TableAlias[] prodA = TableAliasGatherer.Gather(a).ToArray();
TableAlias[] prodB = TableAliasGatherer.Gather(b).ToArray();
for (int i = 0, n = prodA.Length; i < n; i++)
{
this.aliasScope.Add(prodA[i], prodB[i]);
}
}
protected override Expression VisitJoin(JoinExpression join)
{
join = (JoinExpression)base.VisitJoin(join);
if (join.Join == JoinType.CrossApply || join.Join == JoinType.OuterApply)
{
if (join.Right is TableExpression)
{
return(new JoinExpression(JoinType.CrossJoin, join.Left, join.Right, null));
}
else
{
SelectExpression select = join.Right as SelectExpression;
// 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))
{
SelectExpression selectWithoutWhere = select.SetWhere(null);
HashSet <TableAlias> referencedAliases = ReferencedAliasGatherer.Gather(selectWithoutWhere);
HashSet <TableAlias> declaredAliases = TableAliasGatherer.Gather(join.Left);
referencedAliases.IntersectWith(declaredAliases);
if (referencedAliases.Count == 0)
{
Expression where = select.Where;
select = selectWithoutWhere;
var pc = ColumnProjector.ProjectColumns(where, select.Columns, select.Alias, TableAliasGatherer.Gather(select.From));
select = select.SetColumns(pc.Columns);
where = pc.Projector;
JoinType jt = (where == null) ? JoinType.CrossJoin : (join.Join == JoinType.CrossApply ? JoinType.InnerJoin : JoinType.LeftOuter);
return(new JoinExpression(jt, join.Left, select, where));
}
}
}
}
return(join);
}
protected override Expression VisitJoin(JoinExpression join)
{
join = (JoinExpression)base.VisitJoin(join);
if (join.Join == JoinType.CrossJoin && this.currentWhere != null)
{
// try to figure out which parts of the current where expression can be used for a join condition
var declaredLeft = TableAliasGatherer.Gather(join.Left);
var declaredRight = TableAliasGatherer.Gather(join.Right);
var declared = new HashSet <TableAlias>(declaredLeft.Union(declaredRight), TableAlias.Comparer);
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, JoinType.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 TableAlias();
var aliases = TableAliasGatherer.Gather(expression);
var decls = new List <ColumnDeclaration>();
foreach (var ta in aliases)
{
foreach (var col in this.columns[ta])
{
string name = decls.GetAvailableColumnName(col.Name);
var decl = new ColumnDeclaration(name, col, col.SqlType);
decls.Add(decl);
var newCol = new ColumnExpression(col.Type, col.SqlType, newAlias, name);
this.map.Add(col, newCol);
}
}
return(new SelectExpression(newAlias, decls, expression, null));
}
protected override Expression VisitSelect(SelectExpression select)
{
bool saveIsOuterMostSelect = this.isOuterMostSelect;
try
{
this.isOuterMostSelect = false;
var saveSuppressOrderBy = this.suppressOrderby;
this.suppressOrderby = false;
var saveGatheredOrderings = this.gatheredOrderings;
if (saveSuppressOrderBy)
{
this.gatheredOrderings = null;
this.isOuterMostSelect = true;
}
select = (SelectExpression)base.VisitSelect(select);
this.suppressOrderby = saveSuppressOrderBy;
if (saveSuppressOrderBy)
{
this.gatheredOrderings = saveGatheredOrderings;
}
bool hasOrderBy = select.OrderBy != null && select.OrderBy.Count > 0;
bool hasGroupBy = select.GroupBy != null && select.GroupBy.Count > 0;
bool canHaveOrderBy = saveIsOuterMostSelect || select.Take != null || select.Skip != null;
bool canReceiveOrderings = canHaveOrderBy && !hasGroupBy && !select.IsDistinct && !AggregateChecker.HasAggregates(select) && !suppressOrderby;
if (hasOrderBy)
{
this.PrependOrderings(select.OrderBy);
}
if (select.IsReverse)
{
if (this.gatheredOrderings == null || gatheredOrderings.Count == 0)
{
throw new NotSupportedException(string.Format(Res.OperationNotSupported, "", "Reverse", "if no 'OrderBy' expression."));
}
for (int i = 0, n = this.gatheredOrderings.Count; i < n; i++)
{
var ord = this.gatheredOrderings[i];
this.gatheredOrderings[i] =
new OrderExpression(
ord.OrderType == OrderType.Ascending ? OrderType.Descending : OrderType.Ascending,
ord.Expression
);
}
}
IEnumerable <OrderExpression> orderings = null;
if (canReceiveOrderings)
{
orderings = this.gatheredOrderings;
}
else if (canHaveOrderBy)
{
orderings = select.OrderBy;
}
bool canPassOnOrderings = !saveIsOuterMostSelect && !hasGroupBy && !select.IsDistinct && !suppressOrderby;
ReadOnlyCollection <ColumnDeclaration> columns = select.Columns;
if (this.gatheredOrderings != null)
{
if (canPassOnOrderings)
{
var producedAliases = TableAliasGatherer.Gather(select.From);
// reproject order expressions using this select's alias so the outer select will have properly formed expressions
BindResult project = this.RebindOrderings(this.gatheredOrderings, select.Alias, producedAliases, select.Columns);
this.gatheredOrderings = null;
this.PrependOrderings(project.Orderings);
columns = project.Columns;
}
else
{
this.gatheredOrderings = null;
}
}
if (orderings != select.OrderBy || columns != select.Columns || select.IsReverse)
{
select = new SelectExpression(select.Alias, columns, select.From, select.Where, orderings, select.GroupBy, select.IsDistinct, select.Skip, select.Take, false);
}
return(select);
}
finally
{
this.isOuterMostSelect = saveIsOuterMostSelect;
}
}