Linq Query keeps throwing "Unable to create a constant value of type System.Object....", Why?

Question

The following is the code sample:

private void loadCustomer(int custIdToQuery) 
    {
        var dbContext = new SampleDB();
        try
        {
            var customerContext = from t in dbContext.tblCustomers      // keeps throwing:
                                   where t.CustID.Equals(custIdToQuery) // Unable to create a constant value of type 'System.Object'. 
                                   select new                           // Only primitive types ('such as Int32, String, and Guid') 
                                   {                                    // are supported in this context.
                                       branchId = t.CustomerBranchID,   //
                                       branchName = t.BranchName        //
                                   };                                   //

            if (customerContext.ToList().Count() < 1) //Already Tried customerContext.Any()
            {
                lstbCustomers.DataSource = customerContext;
                lstbCustomers.DisplayMember = "branchName";
                lstbCustomers.ValueMember = "branchId";
            }
            else
            {
                lstbCustomers.Items.Add("There are no branches defined for the selected customer.");
                lstbCustomers.Refresh();
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        finally
        {
            dbContext.Dispose();
        }
    }

i am unable to understand what am i doing wrong. I keep getting "Unable to create a constant value of type 'System.Object'. Only primitive types ('such as Int32, String, and Guid') are supported in this context."

score 254 · Accepted Answer · answered Jan 04 '11 at 10:08

254

Use == instead of Equals:

where t.CustID == custIdToQuery

If the types are incorrect you may find that this doesn't compile.

answered Jan 04 '11 at 10:08

Mark Byers

811,555
193
1,581
1,452

11

Can you please explain the difference between "t.CustID == custIdToQuery" and "t.CustID.Equals(custIdToQuery)". thanks in advance – Neel Jan 04 '11 at 10:20
2

@Neel Take a look at this question for explanation on the difference between `==` and `.Equals()`: http://stackoverflow.com/questions/814878/c-sharp-difference-between-and-equals – Alex Jun 02 '16 at 12:52

score 30 · Answer 2 · answered Jul 17 '13 at 20:30

30

I had the same issue with a nullable int. Using == instead works nicely, but if you want to use .Equals, you can compare it to the value of the nullable variable, so

where t.CustID.Value.Equals(custIdToQuery)

answered Jul 17 '13 at 20:30

kloarubeek

2,706
20
24

score 10 · Answer 3 · answered Nov 15 '12 at 18:07

10

I had the same issue when I was trying to do .Equals with a nullable decimal. Using == instead works nicely. I guess this is because it's not trying to match the exact "type" of decimal? to decimal.

answered Nov 15 '12 at 18:07

Dave Stuart

547
8
22

4

Keep in mind that this is in the context of an `IQueryable`, so it's not compiled into regular C# code. It becomes an expression that is passed to a query provider. That query provider can do whatever wants with the query, and it may handle `Equals` and `==` the same or not. – Servy Nov 15 '12 at 18:31
I used `.Equal()` to compare `Int32?` with `Int32`. Since `Int32?` is supposed to contain `Int32` and `null`, I thought it would work. But it didn't. `==` worked. – matrix Nov 04 '13 at 10:59

score 1 · Answer 4 · answered Nov 10 '17 at 07:34

1

I was faced the same issue and i was comparing Collection Object "User" with integer data type "userid" (x.User.Equals(userid))

from user in myshop.UserPermissions.Where(x => x.IsDeleted == false && x.User.Equals(userid))

and correct Query is x.UserId.Equals(userid)

from user in myshop.UserPermissions.Where(x => x.IsDeleted == false && x.UserId.Equals(userid))

answered Nov 10 '17 at 07:34

Satish Kumar sonker

1,250
8
15

This is a different problem, you're comparing apples and oranges. – Lasse V. Karlsen Nov 10 '17 at 07:45
how it's different. while i have faced same issue. i just post this answer for reference only for others. – Satish Kumar sonker Nov 10 '17 at 09:08

score 1 · Answer 5 · answered Nov 16 '19 at 05:18

In my case, I changed the direct call of (sender as Button).Text to indirect call using a temp var, has worked. working code:

private void onTopAccBtnClick(object sender, EventArgs e)
    {
        var name = (sender as Button).Text;
        accountBindingSource.Position =
                    accountBindingSource.IndexOf(_dataService.Db.Accounts.First(ac => ac.AccountName == name));
        accountBindingSource_CurrentChanged(sender, e);
    }

buggy code:

private void onTopAccBtnClick(object sender, EventArgs e)
    {
        accountBindingSource.Position =
                    accountBindingSource.IndexOf(_dataService.Db.Accounts.First(ac => ac.AccountName == (sender as Button).Text));
        accountBindingSource_CurrentChanged(sender, e);
    }

Linq Query keeps throwing "Unable to create a constant value of type System.Object....", Why?

5 Answers5

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