MethodCallExpression CreatePushedExpressionUsingGroupBy(Expression pushable, Expression pushedBefore)
{
TreeNodeReplacer replacer = new TreeNodeReplacer();
List<Expression> separated = Separate(pushable);
Stack<Expression> parts = new Stack<Expression>();
Stack<ParameterExpression> auxs = new Stack<ParameterExpression>();
Expression replaced = pushable;
foreach(Expression s in separated){
parts.Push(s);
auxs.Push(Expression.Parameter(typeof(IGrouping<,>).MakeGenericType(typeof(int), parts.Peek().Type.GetGenericArguments()[0]), makeAuxName()));
replaced = replacer.Replace(replaced, parts.Peek(), auxs.Peek());
}
Expression subexpr = generateSelect(generateGroupBy(parts.Pop(), auxs.Peek().Type.GetGenericArguments()[1]),replaced,auxs.Pop());
ParameterExpression aux = Expression.Parameter(subexpr.Type.GetGenericArguments()[0],makeAuxName());
foreach(Expression part in parts)
{
subexpr = generateSelectMany(generateGroupBy(part, auxs.Peek().Type.GetGenericArguments()[1]), subexpr, auxs.Pop());
}
return generateSelectMany(subexpr, replacer.Replace(pushedBefore, pushable, aux), aux);
}
internal Expression Push(Expression pushable, Expression pushBefore, Expression query)
{
Expression pushed = this.CreatePushedExpressionUsingGroupBy(pushable, pushBefore);
query = new TreeNodeReplacer().Replace(query, pushBefore, pushed);
return query;
}
