My Code:

```
var lastName = employees
   .Where(a => a.Number ==
      (dm.MTM.Where(b => b.MTT.IsManager)
             .Select(c => c.Number)
             .FirstOrDefault()))
   .Select(z => z.LastName)
   .FirstOrDefault();

```

Error Message:

```
Unable to create a constant value of type 'XXX.Models.Mt.MTM'. Only primitive types or enumeration types are supported in this context. 

```