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 VisitGrouping(SqlGrouping g) {
g.Key = this.VisitExpression(g.Key);
g.Group = this.VisitExpression(g.Group);
return g;
}
private Type GenerateGrouping(SqlGrouping grp)
{
Type[] typeArgs = grp.ClrType.GetGenericArguments();
this.GenerateExpressionForType(grp.Key, typeArgs[0]);
this.Generate(grp.Group);
Type orbType = typeof(ObjectMaterializer<>).MakeGenericType(this.compiler.DataReaderType);
MethodInfo miCreateGroup = TypeSystem.FindStaticMethod(orbType, "CreateGroup", new Type[] { typeArgs[0], typeof(IEnumerable<>).MakeGenericType(typeArgs[1]) }, typeArgs);
Diagnostics.Debug.Assert(miCreateGroup != null);
gen.Emit(OpCodes.Call, miCreateGroup);
return miCreateGroup.ReturnType;
}
internal override SqlExpression VisitGrouping(SqlGrouping g)
{
if(!_isDebugMode)
{
throw Error.InvalidFormatNode("Grouping");
}
_commandStringBuilder.Append("Group(");
this.Visit(g.Key);
_commandStringBuilder.Append(", ");
this.Visit(g.Group);
_commandStringBuilder.Append(")");
return g;
}
internal override SqlExpression VisitGrouping(SqlGrouping g)
{
SqlGrouping n = new SqlGrouping(g.ClrType, g.SqlType,
this.VisitExpression(g.Key), this.VisitExpression(g.Group), g.SourceExpression
);
return n;
}
internal override SqlExpression VisitGrouping(SqlGrouping g)
{
g.Key = this.VisitNamedExpression(g.Key, "Key");
g.Group = this.VisitNamedExpression(g.Group, "Group");
return g;
}
internal override SqlExpression VisitGrouping(SqlGrouping g) {
g.Key = this.FetchExpression(g.Key);
g.Group = this.FetchExpression(g.Group);
return g;
}