Question

I am having some trouble with a linq query I am trying to write.

I have List A of products that have been modified so I am trying to get the list of products from the db to allow me to apply the changes to them.

I have tried 2 different queries

   var query = from p in db.Products
                where products.Select(z => z.id).Contains(p.Id)
                select p;

        var query2 = from p in db.Products where (from o in products
                     select o.id)
                    .Contains(p.Id)
                    select p;

Both attempts are returning an error

base {System.SystemException} = {“Unable to create a constant value of type ‘ProjectABC.Models.ProductModel’. Only primitive types (‘such as Int32, String, and Guid’) are supported in this context.”}

What am I doing wrong?

Answer 1

I had the same problem the other day, seems EF doesn’t support Select().Contains() without giving that error. After testing around for a bit, I ended up splitting it up in what in your case would correspond to;

var IDs = products.Select(z=>z.id);
var query = from p in db.Products
            where IDs.Contains(p.Id)
            select p;

which worked well in my case when the “products” collection was in memory anyway (ie a ToList()’ed result from the database)