Trying to pass order by clause as parameter

Question

I was trying to pass orderby clause as a parameter:

public IList<SomeType> GetData(Expression<Func<Customer, object>> order)
{
        if (order==null)
        {
            order =   x => x.PrintOrder ;
        }

        var list = (from c in this.dbContext.Customer
                    where c.Type==1
                    orderby order
                    select new {c.Name }).ToList();

        return list;
}

But this throws an error:

System.InvalidOperationException: could not be translated.
Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList'

Is it possible to add multiple fields to order parameter? – Avinash NG Aug 05 '21 at 06:54 — Avinash NG, Aug 05 '21 at 06:54

score 4 · Accepted Answer · answered Aug 05 '21 at 05:58

4

public IList<Customer> GetData(Expression<Func<Customer, object>> order = null)
    {

    order ??= x => x.PrintOrder;

    //var list = (from c in this.dbContext.Customer
    //             where c.Type==1
    //          orderby order
    //          select c).ToList();
    
    //may works
    return  this.dbContext.Customer.Where(c => c.Type == 1)
                                   .OrderBy(order)
                                   .ToList();
    }

answered Aug 05 '21 at 05:58

jialuo zeng

56
1

as you can see in my question i have not used extension methods. just i am trying with out extension method. since both approaches are same, just i was wondering why that is not working, and if i modify code if (order==null) { order= x => new { x.PrintOrder,x.Sfix } ; } like this, above code also fails to translate – Avinash NG Aug 05 '21 at 06:14
1

@AvinashNG You *have* to use method syntax to be able to pass an expression into the query. This answer is correct. You didn't mention the other ordering in your question. – Gert Arnold Aug 05 '21 at 06:44
@GertArnold, Yes if you use extension method the above answer is right. as you can see i have tried different approach. – Avinash NG Aug 05 '21 at 06:50

PawZaw · Answer 2 · 2021-08-05T11:57:20.567

-1

Update: As suggested in the comments, this method is only suitable for LINQ-to-object situations, if connecting to DB use accepted answear instead

Original answear:

This works:

Func<Customer, object> order = (c) => c.PrintOrder;
var list = (from c in this.dbContext.Customer
        orderby order(c)
        select c).ToList();

The difference is in calling the function order(c), instead of just passing it

You could also use this syntax:

Func<Customer, object> order = (c) => c.PrintOrder;
var list = this.dbContext.Customer.OrderBy(order).ToList();

Take a look at this post: How can I do an OrderBy with a dynamic string parameter?

edited Aug 05 '21 at 11:57

answered Aug 05 '21 at 08:34

PawZaw

1,033
7
15

your first solution is throws the same exception as i asked in my question. Second is similar to the accepted answer. – Avinash NG Aug 05 '21 at 09:43
Also, using `Func` is a serious mistake when applying it to `IQueryable`. – Gert Arnold Aug 05 '21 at 11:51
That's odd, I just tested this in linqpad and it worked (I replaced the source with normal list). – PawZaw Aug 05 '21 at 11:51
So test it in the same circumstances as the question. This is not LINQ to objects. – Gert Arnold Aug 05 '21 at 11:52
I based my answer on this post: https://stackoverflow.com/a/10413311/12417800 – PawZaw Aug 05 '21 at 11:55

Trying to pass order by clause as parameter

2 Answers2