private SqlNode VisitGroupBy(Expression sequence, LambdaExpression keyLambda, LambdaExpression elemLambda, LambdaExpression resultSelector)
{
// Convert seq.Group(elem, key) into
//
// SELECT s.key, MULTISET(select s2.elem from seq AS s2 where s.key == s2.key)
// FROM seq AS s
//
// where key and elem can be either simple scalars or object constructions
//
SqlSelect seq = this.VisitSequence(sequence);
seq = this.LockSelect(seq);
SqlAlias seqAlias = new SqlAlias(seq);
SqlAliasRef seqAliasRef = new SqlAliasRef(seqAlias);
// evaluate the key expression relative to original sequence
_parameterExpressionToSqlExpression[keyLambda.Parameters[0]] = seqAliasRef;
SqlExpression keyExpr = this.VisitExpression(keyLambda.Body);
// make a duplicate of the original sequence to use as a foundation of our group multiset
SqlDuplicator sd = new SqlDuplicator();
SqlSelect selDup = (SqlSelect)sd.Duplicate(seq);
// rebind key in relative to the duplicate sequence
SqlAlias selDupAlias = new SqlAlias(selDup);
SqlAliasRef selDupRef = new SqlAliasRef(selDupAlias);
_parameterExpressionToSqlExpression[keyLambda.Parameters[0]] = selDupRef;
SqlExpression keyDup = this.VisitExpression(keyLambda.Body);
SqlExpression elemExpr = null;
SqlExpression elemOnGroupSource = null;
if(elemLambda != null)
{
// evaluate element expression relative to the duplicate sequence
_parameterExpressionToSqlExpression[elemLambda.Parameters[0]] = selDupRef;
elemExpr = this.VisitExpression(elemLambda.Body);
// evaluate element expression relative to original sequence
_parameterExpressionToSqlExpression[elemLambda.Parameters[0]] = seqAliasRef;
elemOnGroupSource = this.VisitExpression(elemLambda.Body);
}
else
{
// no elem expression supplied, so just use an alias ref to the duplicate sequence.
// this will resolve to whatever was being produced by the sequence
elemExpr = selDupRef;
elemOnGroupSource = seqAliasRef;
}
// Make a sub expression out of the key. This will allow a single definition of the
// expression to be shared at multiple points in the tree (via SqlSharedExpressionRef's)
SqlSharedExpression keySubExpr = new SqlSharedExpression(keyExpr);
keyExpr = new SqlSharedExpressionRef(keySubExpr);
// construct the select clause that picks out the elements (this may be redundant...)
SqlSelect selElem = new SqlSelect(elemExpr, selDupAlias, _dominatingExpression);
selElem.Where = _nodeFactory.Binary(SqlNodeType.EQ2V, keyExpr, keyDup);
// Finally, make the MULTISET node. this will be used as part of the final select
SqlSubSelect ss = _nodeFactory.SubSelect(SqlNodeType.Multiset, selElem);
// add a layer to the original sequence before applying the actual group-by clause
SqlSelect gsel = new SqlSelect(new SqlSharedExpressionRef(keySubExpr), seqAlias, _dominatingExpression);
gsel.GroupBy.Add(keySubExpr);
SqlAlias gselAlias = new SqlAlias(gsel);
SqlSelect result = null;
if(resultSelector != null)
{
// Create final select to include construction of group multiset
// select new Grouping { Key = key, Group = Multiset(select elem from seq where match) } from ...
Type elementType = typeof(IGrouping<,>).MakeGenericType(keyExpr.ClrType, elemExpr.ClrType);
SqlExpression keyGroup = new SqlGrouping(elementType, _typeProvider.From(elementType), keyExpr, ss, _dominatingExpression);
SqlSelect keyGroupSel = new SqlSelect(keyGroup, gselAlias, _dominatingExpression);
SqlAlias kgAlias = new SqlAlias(keyGroupSel);
SqlAliasRef kgAliasRef = new SqlAliasRef(kgAlias);
_parameterExpressionToSqlExpression[resultSelector.Parameters[0]] = _nodeFactory.Member(kgAliasRef, elementType.GetProperty("Key"));
_parameterExpressionToSqlExpression[resultSelector.Parameters[1]] = kgAliasRef;
// remember the select that has the actual group (for optimizing aggregates later)
_sqlNodeToGroupInfo[kgAliasRef] = new GroupInfo { SelectWithGroup = gsel, ElementOnGroupSource = elemOnGroupSource };
SqlExpression resultExpr = this.VisitExpression(resultSelector.Body);
result = new SqlSelect(resultExpr, kgAlias, _dominatingExpression);
// remember the select that has the actual group (for optimizing aggregates later)
_sqlNodeToGroupInfo[resultExpr] = new GroupInfo { SelectWithGroup = gsel, ElementOnGroupSource = elemOnGroupSource };
}
else
{
// Create final select to include construction of group multiset
// select new Grouping { Key = key, Group = Multiset(select elem from seq where match) } from ...
Type elementType = typeof(IGrouping<,>).MakeGenericType(keyExpr.ClrType, elemExpr.ClrType);
SqlExpression resultExpr = new SqlGrouping(elementType, _typeProvider.From(elementType), keyExpr, ss, _dominatingExpression);
result = new SqlSelect(resultExpr, gselAlias, _dominatingExpression);
// remember the select that has the actual group (for optimizing aggregates later)
_sqlNodeToGroupInfo[resultExpr] = new GroupInfo { SelectWithGroup = gsel, ElementOnGroupSource = elemOnGroupSource };
}
return result;
}
internal virtual SqlExpression VisitSharedExpression(SqlSharedExpression shared) {
shared.Expression = this.VisitExpression(shared.Expression);
return shared;
}
internal SqlSharedExpressionRef(SqlSharedExpression expr)
: base(SqlNodeType.SharedExpressionRef, expr.ClrType, expr.SourceExpression)
{
this.expr = expr;
}
internal override SqlExpression VisitSharedExpression(SqlSharedExpression shared)
{
return this.VisitExpression(shared.Expression);
}
internal override SqlExpression VisitSharedExpression(SqlSharedExpression shared)
{
if(!_isDebugMode)
{
throw Error.InvalidFormatNode("Shared");
}
_commandStringBuilder.Append("SHARED(");
this.Visit(shared.Expression);
_commandStringBuilder.Append(")");
return shared;
}
internal override SqlExpression VisitSharedExpression(SqlSharedExpression sub)
{
SqlSharedExpression n = new SqlSharedExpression(sub.Expression);
this.nodeMap[sub] = n;
n.Expression = this.VisitExpression(sub.Expression);
return n;
}
internal override SqlExpression VisitSharedExpression(SqlSharedExpression shared)
{
throw Error.UnexpectedSharedExpression();
}
internal SqlSharedExpressionRef(SqlSharedExpression expr)
: base(SqlNodeType.SharedExpressionRef, expr.ClrType, expr.SourceExpression) {
this.expr = expr;
}
internal override SqlExpression VisitSharedExpression(SqlSharedExpression shared) {
shared.Expression = this.VisitExpression(shared.Expression);
// shared expressions in group-by/select must be only column refs
if (shared.Expression.NodeType == SqlNodeType.ColumnRef) {
return shared.Expression;
}
else {
// not simple? better push it down (make a sub-select that projects the relevant bits
shared.Expression = this.PushDownExpression(shared.Expression);
return shared.Expression;
}
}
