protected virtual Expression VisitScalar(ScalarExpression node)
{
var select = (SelectExpression) Visit(node.Select);
if (select != node.Select)
{
return new ScalarExpression(node.Type, select);
}
return node;
}
// private methods
private Expression BindAggregate(Expression source, String aggName, MethodInfo method, LambdaExpression argument,
Boolean isRoot)
{
Type returnType = method.ReturnType;
Boolean hasPredicateArg = HasPredicateArg(aggName);
Boolean isDistinct = false;
Boolean argumentWasPredicate = false;
// check for distinct
var mcs = source as MethodCallExpression;
if (mcs != null && !hasPredicateArg && argument == null)
{
if (mcs.Method.Name == "Distinct" && mcs.Arguments.Count == 1 &&
(mcs.Method.DeclaringType == typeof (Queryable) || mcs.Method.DeclaringType == typeof (Enumerable)))
{
source = mcs.Arguments[0];
isDistinct = true;
}
}
if (argument != null && hasPredicateArg)
{
// convert query.Count(predicate) into query.Where(predicate).Count()
source = Expression.Call(typeof (Queryable), "Where", method.GetGenericArguments(), source, argument);
argument = null;
argumentWasPredicate = true;
}
ProjectionExpression projection = VisitSequence(source);
Expression argExpr = null;
if (argument != null)
{
_map[argument.Parameters[0]] = projection.Projector;
argExpr = Visit(argument.Body);
}
else if (!hasPredicateArg)
{
argExpr = projection.Projector;
}
SourceAlias alias = GetNextAlias();
Expression aggExpr = new AggregateExpression(returnType, aggName, argExpr, isDistinct);
var select = new SelectExpression(alias, new[] {new ColumnDeclaration("", aggExpr)}, projection.Source, null);
if (isRoot)
{
ParameterExpression p = Expression.Parameter(typeof (IEnumerable<>).MakeGenericType(aggExpr.Type),
"node");
LambdaExpression gator =
Expression.Lambda(Expression.Call(typeof (Enumerable), "Single", new[] {returnType}, p), p);
return new ProjectionExpression(select, new ColumnExpression(returnType, alias, ""), gator);
}
var subquery = new ScalarExpression(returnType, select);
// if we can find the corresponding group-info we can build a special AggregateSubquery node that will enable us to
// optimize the node expression later using AggregateRewriter
GroupByInfo info;
if (!argumentWasPredicate && _groupByMap.TryGetValue(projection, out info))
{
// use the element expression from the group-by info to rebind the argument so the resulting expression is one that
// would be legal to add to the _columns in the select expression that has the corresponding group-by clause.
if (argument != null)
{
_map[argument.Parameters[0]] = info.Element;
argExpr = Visit(argument.Body);
}
else if (!hasPredicateArg)
{
argExpr = info.Element;
}
aggExpr = new AggregateExpression(returnType, aggName, argExpr, isDistinct);
// check for easy to optimize case. If the projection that our node is based on is really the 'group' argument from
// the query.GroupBy(xxx, (key, group) => yyy) method then whatever expression we return here will automatically
// become part of the select expression that has the group-by clause, so just return the simple node expression.
if (projection == _currentGroupElement)
{
return aggExpr;
}
return new AggregateSubqueryExpression(info.Alias, aggExpr, subquery);
}
return subquery;
}