LINQ Complied queries giving error : There is no implicit reference conversion from 'Chinook.ChinookModel' to 'System.Data.Entity.Core.Objects.ObjectContext'.

ExplorerJK
ExplorerJK used Ask the Experts™
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Hi,

I have a class" Employee" and DBcontext : ChinookModel (.Net 4.5) , however when I try to create compiled query it gives the following error : ( Any help is appreciated, Thanks in advance )

Error
1
The type 'Chinook.ChinookModel' cannot be used as type parameter 'TArg0' in the generic type or method 'System.Data.Entity.Core.Objects.CompiledQuery.Compile<TArg0,TArg1,TResult>(System.Linq.Expressions.Expression<System.Func<TArg0,TArg1,TResult>>)'. There is no implicit reference conversion from 'Chinook.ChinookModel' to 'System.Data.Entity.Core.Objects.ObjectContext'.
C:\Users\Bond009\documents\visual studio 2013\Projects\Chinook\Chinook\DAL\Queries.cs
18
12
Chinook
I am using the following code to create LINQ complied query:

namespace Chinook
{
    public class StaticQueries
    {
        static readonly Func<ChinookModel, int, IQueryable<Employee>> getemployeebyid =
           CompiledQuery.Compile<ChinookModel, int, IQueryable<Employee>>
           ((ctx, tempid) => from c in ctx.Employees
                             where c.EmployeeId == tempid
                             select c);
    }
}

====================Employee Class ======================

    [Table("Employee")]
    public partial class Employee
    {
        public Employee()
        {
            Customers = new HashSet<Customer>();
            Employee1 = new HashSet<Employee>();
        }

        public int EmployeeId { get; set; }

        [Required]
        [StringLength(20)]
        public string LastName { get; set; }

        [Required]
        [StringLength(20)]
        public string FirstName { get; set; }

        [StringLength(30)]
        public string Title { get; set; }

        public int? ReportsTo { get; set; }

        public DateTime? BirthDate { get; set; }

        public DateTime? HireDate { get; set; }

        [StringLength(70)]
        public string Address { get; set; }

        [StringLength(40)]
        public string City { get; set; }

        [StringLength(40)]
        public string State { get; set; }

        [StringLength(40)]
        public string Country { get; set; }

        [StringLength(10)]
        public string PostalCode { get; set; }

        [StringLength(24)]
        public string Phone { get; set; }

        [StringLength(24)]
        public string Fax { get; set; }

        [StringLength(60)]
        public string Email { get; set; }

        public virtual ICollection<Customer> Customers { get; set; }

        public virtual ICollection<Employee> Employee1 { get; set; }

        public virtual Employee Employee2 { get; set; }
    }

=====================ChinookModel - Dbcontext =====================

public partial class ChinookModel : DbContext
    {
        public ChinookModel()
            : base("name=Chinook")
        {
        }

        public virtual DbSet<Album> Albums { get; set; }
        public virtual DbSet<Artist> Artists { get; set; }
        public virtual DbSet<Customer> Customers { get; set; }
        public virtual DbSet<Employee> Employees { get; set; }
        public virtual DbSet<Genre> Genres { get; set; }
        public virtual DbSet<Invoice> Invoices { get; set; }
        public virtual DbSet<InvoiceLine> InvoiceLines { get; set; }
        public virtual DbSet<MediaType> MediaTypes { get; set; }
        public virtual DbSet<Playlist> Playlists { get; set; }
        public virtual DbSet<Track> Tracks { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Artist>()
                .HasMany(e => e.Albums)
                .WithRequired(e => e.Artist)
                .WillCascadeOnDelete(false);

            modelBuilder.Entity<Customer>()
                .HasMany(e => e.Invoices)
                .WithRequired(e => e.Customer)
                .WillCascadeOnDelete(false);

            modelBuilder.Entity<Employee>()
                .HasMany(e => e.Customers)
                .WithOptional(e => e.Employee)
                .HasForeignKey(e => e.SupportRepId);

            modelBuilder.Entity<Employee>()
                .HasMany(e => e.Employee1)
                .WithOptional(e => e.Employee2)
                .HasForeignKey(e => e.ReportsTo);
        }
        public int ThisID { get; set; }
    }
======================================================
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Software Architect
Commented:
The error is indicating that ChinookModel is not derived from ObjectContext.
In this case ChinookModel is derived from DbContext which is the current recommended context to use with .NET 4.5 . (see the link DBContext or Object Context which states:
    Models created in Visual Studio 2012 & 2013 will generate simple POCO entity classes and a context that derives from the simplified DbContext.
    Models created in Visual Studio 2010 will generate entity classes that derive from EntityObject and a context that derives from ObjectContext.
    Note: In Visual Studio 2010 we recommend switching to the DbContext Generator template once you've added your model.
).
This might have worked with earlier versions say 4.1, because EF created an object derived from ObjectContext instead of DbContext for us to manage our entities.
If you are targeting .NET 4.5 and EF (Entity Framework 5.0), we may no more need compiled queries as queries shall be cached automatically for you, as this post explains. Automatic Caching EF5
If you are not convinced, still want to use Compiled Queries, then you can switch back your ChinookModel to be derived from ObjectContext. But before that you may want to consider this article as well. Compiled or Bust?

Hope this helps,
Thanks,
Karrtik
Karrtik IyerSoftware Architect

Commented:
May I please know why is this a grade B, I have explained the reason why error was coming and what are the possible way to solve it?

Author

Commented:
My bad ....I am new to this grading.. system....please change to A... Thanks Karrtik.
sadasd

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