Question

I know there have been a lot of questions about Entity Framework doing cross database queries on the same server posted to stackoverflow. Mostly the answer seems to be ‘no’, and this link from way back in 2008 is referenced. However, Entity Framework is changing all the time and with CTP5 out, I’m wondering if the answer is still the same – that you can’t do it, or you can do it if you manually edit the edmx file, or you have to use views. This feature alone is the reason I’m still tied to Linq-to-SQL, as we have multiple SQL Server 2008 databases on the same server and need to query across them. Polluting our databases with hundreds of select * views is not an option, and with code-first development I don’t have an edmx file to edit. I was playing with the pubs database to see if I could get somewhere, but I’m stuck. Any suggestions?

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration;

namespace DbSchema {
    public class Employee {
        [Key]
        public string ID { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public short JobID { get; set; }
        public Job Job { get; set; }
    }

    public class Job {
        [Key]
        public short ID { get; set; }
        public string Description { get; set; }
    }

    public class PubsRepository : DbContext {
        public DbSet<Employee> Employee { get; set; }
        public DbSet<Job> Job { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder) {
            // employee
            var eeMap = modelBuilder.Entity<Employee>();
            eeMap.ToTable("employee", "dbo"); // <-- how do I reference another database?
            eeMap.Property(e => e.ID).HasColumnName("emp_id");
            eeMap.Property(e => e.FirstName).HasColumnName("fname");
            eeMap.Property(e => e.LastName).HasColumnName("lname");
            eeMap.Property(e => e.JobID).HasColumnName("job_id");

            // job
            var jobMap = modelBuilder.Entity<Job>();
            jobMap.Property(j => j.ID).HasColumnName("job_id");
            jobMap.Property(j => j.Description).HasColumnName("job_desc");
        }

        public List<Employee> GetManagers() {
            var qry = this.Employee.Where(x => x.Job.Description.Contains("manager"));
            Debug.WriteLine(qry.ToString());
            return qry.ToList(); // <-- error here when referencing another database!
        }
    }
}

Answer 1

I think that the answer is still no, but there are ways around it.

The reason why it is no, it that EF uses a DBContext, and a context has a connection string, and a connection string goes to a database.

Here are 2 ways around it:

• use 2 different contexts one against each database, this will mean bringing data to the client and merging it on the client.
• use linked tables on the database, pulling data through views, so that EF sees it as coming from a single database.

In your code it looks like you are using 2 dbcontexts