DbSet, ModelBuilder, and EF Navigation Properties

Question

I'm attempting to implement a multi-tenant application where I query the db via the tenant object, instead of directly off the context. Before I had this:

public User GetUserByEmail(string email)
    {
        using (var db = CreateContext())
        {
            return db.Users.FirstOrDefault(u => u.Email.Equals(email, StringComparison.OrdinalIgnoreCase));
        }
    }

Now I have this:

public User GetUserByEmail(string email)
    {
        using (var db = CreateContext())
        {
            return _tenant.Users.FirstOrDefault(u => u.Email.Equals(email, StringComparison.OrdinalIgnoreCase));
        }
    }

Where Tenant is the following:

public class Tenant
{
    public Tenant()
    {
    }

    [Key]
    [Required]
    public int TenantId { get; set; }

    public virtual DbSet<User> Users { get; set; }
    // etc
}

Where my User model has the following:

public virtual List<Tenant> Tenants { get; set; }

And in my Context configuration, I have the following:

modelBuilder.Entity<Tenant>()
        .HasMany(e => e.Users)
        .WithMany()
        .Map(m =>
        {
            m.ToTable("UserTenantJoin");
            m.MapLeftKey("TenantId");
            m.MapRightKey("UserId");
        });

But I'm running into a problem with the fact that DbSet is incompatible with the ModelBuilder above - it chokes on HasMany saying that the use of DbSet cannot be inferred from usage.

I played with using ICollection instead, but then in my service layer all calls to _tenant.Users.Include(stuff), or Find(), and other db queries break.

Example of a service method that breaks if I use ICollection:

   public User GetUserWithInterestsAndAptitudes(string username)
    {
        using (var db = CreateContext())
        {
            return _tenant.Users.  // can't use .Include on ICollection
                Include(u => u.Relationships).
                Include(u => u.Interests).
                Include(u => u.Interests.Select(s => s.Subject)).
                Include(u => u.Interests.Select(s => s.Aptitude)).
                FirstOrDefault(s => s.Username.Equals(username, StringComparison.OrdinalIgnoreCase));
        }
    }

I'm hoping there's a solution that will allow me to keep the navigation properties queryable without re-architecting my service layer.

One option is that I revert everything back to using the context via db.Users, and then add another condition to every single query .Where(u => u.TenantId == _tenant.TenantId) - but I'm trying to avoid this.

Any help here would be much appreciated.

Answer 1

I have a solution similar to what you are trying to avoid.

I have a real DbContext that is only accessed via a TenantContext.

public class RealContext
{
     public DbSet<User> Users { get; set; }
     [...]
}

public class TenantContext 
{
    private RealContext realContext;
    private int tenantId;
    public TenantContext(int tenantId)
    {
        realContext = new RealContext();
        this.tenantId= tenantId;
    }
    public IQueryable<User> Users { get { FilterTenant(realContext.Users); }     }

    private IQueryable<T> FilterTenant<T>(IQueryable<T> values) where T : class, ITenantData
    {
         return values.Where(x => x.TenantId == tenantId);
    }
    public int SaveChanges()
    {
        ApplyTenantIds();
        return realContext.SaveChanges();
    }
}

Using this method I'm sure that there is no was a query can be sent without getting the correct tenants. For adding and removing items from the context I' using those two generic methods.

public void Remove<T>(params T[] items) where T : class, ITenantData
{
    var set = realContext.Set<T>();
    foreach(var item in items)
        set.Remove(item);
}

public void Add<T>(params T[] items) where T : class, ITenantData
{
    var set = realContext.Set<T>();
    foreach (var item in items)
        set.Add(item);
}