实体框架7 DbContext OnModelCreating为ApplicationUser字段指定外键

Question

I am trying to achieve something very similar to what is happening in this EF7 fluent API documentation , but it is not the exact case.

I have a model that looks like this:

public class BlogPost
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public string CreatedBy {get; set; }

    public ApplicationUser CreatedByUser { get; set; }
}

My ApplicationUser class does not have anything related to BlogPost in it. So the connection doesn't really need to go both ways.

Can someone tell me how for my situation how I can tell entity framework that I want to populate CreatedByUser when using Include based on the CreatedBy field in BlogPost equaling the Username field in AspNetUsers table?

Here is what I want to be able to do in my repository:

using (var blogContext = new BlogContext())
{
  return blogContext .BlogPosts
    .Include(bp => bp.CreatedByUser)
}

This is my best attempt:

protected override void OnModelCreating(ModelBuilder builder)
{
    builder.Entity<BlogPost>()
        .HasOne(fp => fp.CreatedByUser)
        .WithMany()
        .HasForeignKey(fp => fp.CreatedBy)
        .IsRequired();
}

I feel like the trick here is not adding a parameter to .WithMany() since in my model I do not have a List property inside of my ApplicationUser model.

The main thing that is causing me issues is that by default EF is trying to use the Id field as the key in the AspNetUsers table. I want to tell it to use Username as the key, not the guid.

Answer 1

I figured out a solution that is working perfectly on my end.

Here is the Fluent API code that needs to be put in your DbContext file in order to get this to work:

protected override void OnModelCreating(ModelBuilder builder)
{
    base.OnModelCreating(builder);

    // Need to do this because if using as a foreign key it must match the length of the principal key
    builder.Entity<BlogPost>()
        .Property(fp => fp.CreatedBy)
        .HasMaxLength(256);

    // A BlogPost has one CreatedByUser (notice we must specify the PrincipalKey to be UserName from the AspNetUsers table otherwise EF would attempt to use the Id (Guid) field by default)
    builder.Entity<BlogPost>()
        .HasOne(bp => bp.CreatedByUser)
        .WithMany()
        .HasForeignKey(bp => bp.CreatedBy)
        .HasPrincipalKey(u => u.UserName)
        .IsRequired();
}

Then in my repository I can simply do the following to make sure CreatedByUser is bound:

public IEnumerable<BlogPost> GetBlogPosts()
{
    return _context.BlogPosts
    .Include(bp => bp.CreatedByUser)
    .ToList();
}

Here is what my models look like:

public class BlogPost
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    // Foreign Key
    public string CreatedBy { get; set; }
    // Navigation Property
    public ApplicationUser CreatedByUser { get; set; }
}

public class ApplicationUser : IdentityUser
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

Since almost all of my objects have a CreatedBy field where I will need to obtain the entire User to be able to display things like FirstName, LastName, Email in my Views I am assuming I will be doing this a lot. I will probably rarely ever need to retrieve a list of any of my entities through the user, but if I did I would add a List MyObjects to ApplicationUser model and then specify something in the .WithMany(b => b.MyObjects) params.

If anyone has any feedback or additional comments please let me know.