Entity Framework V1, PredicateBuilder, Linq to Entities failed to resolve method

Question

Helo,

i have the following code which should filter entities. Half of the code is working by i'm trying to refactor my code to get some sort of 'subfilters'.

Basically i have the following call to filter a Users entity collection:

var result = ctx.GetUsers().WithGroups("Administrators","Users").ToList();

WithGroups has the following definition which works:

public static IQueryable<User> WithGroups(this IQueryable<User> users, params string[] groups)
{
    if (groups != null && groups.Length > 0)
    {

        var outer = PredicateBuilder.True<User>();
        var inner = PredicateBuilder.False<Group>();
        foreach (string group in groups)
        {
            string g1 = group;
            inner = inner.Or(g => g.Name == g1);
        }
        outer = outer.And(u => u.Groups.Where(inner.Compile()).Any());
        users = users.Where(outer);               
    }
    return users;
}

I'm now trying to create a filter on the Groups entities named "WithNames" which i may call within "WithGroups" to get better code. It is defined like so, which works when called directly:

public static IQueryable<Group> WithNames(this IQueryable<Group> groups, params string[] names)
{
    if (names != null && names.Length > 0)
    {
        var outer = PredicateBuilder.True<Group>();
        var inner = PredicateBuilder.False<Group>();
        foreach (var name in names)
        {
            string _n = name;
            inner = inner.Or(g => g.Name == _n);
        }
        groups = groups.Where(outer.And(inner.Expand()));
    }
    return groups;
}

var test = ctx.GetGroups().WithNames("Administrators").ToList();

I have tried this one (and some others) which doesn't work because Linq to Entities doesn't know "WithNames":

public static IQueryable<User> WithGroups(this IQueryable<User> users, params string[] groups)
{
    if (groups != null && groups.Length > 0)
    {
        var inner = PredicateBuilder.False<User>();
        inner = inner.And(u => u.Groups.AsQueryable().AsExpandable().WithNames(groups).Any());
        users = users.Where(inner.Expand());
    }
    returnh users;
}

Perhaps someone may point me to a solution. I don't have any more ideas to find a way to get around this.

Thx

Answer 1

If you change (or overload) your WithNames and WithGroups to return Expression<Func<Group, bool>> instead of IQueryable<Group> (and similarly for Users, then you can use both of them inside calls to Where. As you've discovered, L2E won't parse (this would essentially require decompiling it) a method, but it can handle an Expression.