protected override Expression VisitAggregate(AggregateExpression aggregate)
{
sb.Append(GetAggregateName(aggregate.AggregateType));
sb.Append("(");
if (aggregate.Argument != null)
{
this.Visit(aggregate.Argument);
}
else if (RequiresAsteriskWhenNoArgument(aggregate.AggregateType))
{
sb.Append("*");
}
sb.Append(")");
return(aggregate);
}
private Expression BindAggregate(Expression source, MethodInfo method, LambdaExpression argument, bool isRoot)
{
Type returnType = method.ReturnType;
AggregateType aggType = this.GetAggregateType(method.Name);
bool hasPredicateArg = this.HasPredicateArg(aggType);
bool argumentWasPredicate = false;
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 = this.VisitSequence(source);
Expression argExpr = null;
if (argument != null)
{
this.map[argument.Parameters[0]] = projection.Projector;
argExpr = this.Visit(argument.Body);
}
else if (!hasPredicateArg)
{
argExpr = projection.Projector;
}
string alias = this.GetNextAlias();
var pc = this.ProjectColumns(projection.Projector, alias, projection.Source.Alias);
Expression aggExpr = new AggregateExpression(returnType, aggType, argExpr);
Type selectType = typeof(IEnumerable <>).MakeGenericType(returnType);
SelectExpression select = new SelectExpression(selectType, alias, new ColumnDeclaration[] { new ColumnDeclaration("", aggExpr) }, projection.Source, null);
if (isRoot)
{
ParameterExpression p = Expression.Parameter(selectType, "p");
LambdaExpression gator = Expression.Lambda(Expression.Call(typeof(Enumerable), "Single", new Type[] { returnType }, p), p);
return(new ProjectionExpression(select, new ColumnExpression(returnType, alias, ""), gator));
}
SubqueryExpression subquery = new SubqueryExpression(returnType, select);
// if we can find the corresponding group-info we can build a special AggregateSubquery node that will enable us to
// optimize the aggregate expression later using AggregateRewriter
GroupByInfo info;
if (!argumentWasPredicate && this.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)
{
this.map[argument.Parameters[0]] = info.Element;
argExpr = this.Visit(argument.Body);
}
else if (!hasPredicateArg)
{
argExpr = info.Element;
}
aggExpr = new AggregateExpression(returnType, aggType, argExpr);
// check for easy to optimize case. If the projection that our aggregate 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 aggregate expression.
if (projection == this.currentGroupElement)
{
return(aggExpr);
}
return(new AggregateSubqueryExpression(info.Alias, aggExpr, subquery));
}
return(subquery);
}