protected DbAggregateExpression UpdateAggregate(DbAggregateExpression aggregate, Type type,
DbAggregateType aggType, Expression arg, bool isDistinct)
{
if (type != aggregate.Type || aggType != aggregate.AggregateType ||
arg != aggregate.Argument || isDistinct != aggregate.IsDistinct)
return new DbAggregateExpression(type, aggType, arg, isDistinct);
return aggregate;
}
protected virtual Expression VisitAggregate(DbAggregateExpression aggregate)
{
Expression arg = Visit(aggregate.Argument);
return UpdateAggregate(aggregate, aggregate.Type,
aggregate.AggregateType, arg, aggregate.IsDistinct);
}
protected override Expression VisitAggregate(DbAggregateExpression aggregate)
{
this.hasAggregate = true;
return aggregate;
}
private Expression BindAggregate(Expression source, MethodInfo method, LambdaExpression argument, bool isRoot)
{
Type returnType = method.ReturnType;
DbAggregateType aggType = this.GetAggregateType(method.Name);
bool hasPredicateArg = this.HasPredicateArg(aggType);
bool isDistinct = false;
bool argumentWasPredicate = false;
bool useAlternateArg = false;
// check for distinct
MethodCallExpression 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))
&& this.mapping.Language.AllowDistinctInAggregates)
{
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;
}
DbProjectionExpression 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 || useAlternateArg)
{
argExpr = projection.Projector;
}
var alias = this.GetNextAlias();
var pc = this.ProjectColumns(projection.Projector, alias, projection.Select.Alias);
Expression aggExpr = new DbAggregateExpression(returnType, aggType, argExpr, isDistinct);
DbSelectExpression select = new DbSelectExpression(alias, new DbColumnDeclaration[] { new DbColumnDeclaration("", aggExpr) }, projection.Select, null);
if (isRoot)
{
ParameterExpression p = Expression.Parameter(typeof(IEnumerable<>).MakeGenericType(aggExpr.Type), "p");
LambdaExpression gator = Expression.Lambda(Expression.Call(typeof(Enumerable), "Single", new Type[] { returnType }, p), p);
return new DbProjectionExpression(select, new DbColumnExpression(returnType, null, alias, ""), gator);
}
DbScalarExpression subquery = new DbScalarExpression(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 || useAlternateArg)
{
argExpr = info.Element;
}
aggExpr = new DbAggregateExpression(returnType, aggType, argExpr, isDistinct);
// 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 DbAggregateSubqueryExpression(info.Alias, aggExpr, subquery);
}
return subquery;
}
protected override Expression VisitAggregate(DbAggregateExpression aggregate)
{
this.Write(GetAggregateName(aggregate.AggregateType));
this.Write("(");
if (aggregate.IsDistinct)
{
this.Write("DISTINCT ");
}
if (aggregate.Argument != null)
{
this.VisitValue(aggregate.Argument);
}
else if (RequiresAsteriskWhenNoArgument(aggregate.AggregateType))
{
this.Write("*");
}
this.Write(")");
return aggregate;
}
protected virtual bool CompareAggregate(DbAggregateExpression a, DbAggregateExpression b)
{
return (a.AggregateType == b.AggregateType && Compare(a.Argument, b.Argument));
}