Using LINQ intersect function with a non-primitive type

I'm using ENtity Framework with Code First. I have a list of objects that are being passed to a function, which will use the Intersect function from the DatabaseContext and pass the objects. It's not working. Here's the code:

public void BeginProcess(IEnumerable<Contract> selectedContracts)
    {

        DatabaseContext dc= new DatabaseContext();

        var contract = dc.Contracts.Intersect<Contract>(selectedContracts, new ContractComparer());


        foreach (var item in contract)
        {
        开发者_如何学运维    item.BatchNumber = 10;
        }
        //odc.Contracts.Intersect(selectedContracts).ToList().ForEach(x=>x.BatchNumber = batchNum);
        odc.SaveChanges();

    }

I created a ContractComparer class which implements IEqualityComparer:

public class ContractComparer : IEqualityComparer<Contract>
    {

        #region IEqualityComparer<Contract> Members

        public bool Equals(Contract x, Contract y)
        {
            //Check whether the compared objects reference the same data.
            if (Object.ReferenceEquals(x, y)) return true;

            //Check whether any of the compared objects is null.
            if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
                return false;

            return x.OID == y.OID;
        }

        public int GetHashCode(Contract obj)
        {
            return base.GetHashCode();
        }

        #endregion
    }

The error i get is:

LINQ to Entities does not recognize the method 'System.Linq.IQueryable1[Contract] Intersect[Contract](System.Linq.IQueryable1[Contract], System.Collections.Generic.IEnumerable1[Contract], System.Collections.Generic.IEqualityComparer1[Contract])' method, and this method cannot be translated into a store expression.

Any ideas? Thanks.

---

How about;

var contract = dc.Contracts
    .Where(c => selectedContracts.Select(x => x.OID).ToList().Contains(c.OID));

---

Many poeple think that whatever they can do by linq-to-objects, can be done by linq-to-entities too - That's not correct. Prevalent examples are trying to use .ToString(), .SubString(), .Intersect(), etc.

To intersecting entity sets in L2E, you should use .Contains() method:

var contract = from c in db.Contracts
                       where selectedContracts.Contains(c.ContractID)
                       select c;