Unable to implement database model relationships

Question

I'm having problem on my application with postgres. For background I am trying to implement this DB Model:

public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }

    public List<Post> Posts { get; set; }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    public int BlogId { get; set; }
    public Blog Blog { get; set; }
}

I was properly able to create database in Postgres, connect my .Net application to the database etc. the only thing holding me back is after I save an object:

var blog = new Blog();
blog.Url = "UrlTest";

var post = new List<Post>();
var entry = new Post();
post.Title = "Entry Title";
post.Add(entry);

blog.Posts = post;
context.Blog.Add(blog);
context.SaveChanges();

Just a straight forward one to many relationship. After saving the changes, I query the context and it is able to see the relationship of the Blog and Post that I just created.

Unfortunately when I restart my .Net Core App and try to list all Blog then it will show as null but when I went to the Database Server and query Post table I am able to confirm that it still have the Blog Id.

I tried all suggestions below but nothing works on my end: Entity framework code-first null foreign key

Edit: Here is my DbContext:

 protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Blog>();
        modelBuilder.Entity<Post>();
        modelBuilder.Entity<Blog>()
            .HasMany(c => c.Post)
            .WithOne(c => c.Blog)
            .HasForeignKey(c => c.BlogId)
            .OnDelete(deleteBehavior: DeleteBehavior.Cascade);
        base.OnModelCreating(modelBuilder);
    }

    public DbSet<Post> Posts { get; set; }
    public DbSet<Blog> Blogs { get; set; }

I also tried putting virtual on List in Blog Model and Blog in Post Model but didn't work

You need to show your DBContext class as well as the class where you fetch the context and tries to get the list — Anonymous, Jun 25 '19 at 05:38
You should take a look at https://learn.microsoft.com/en-us/ef/core/querying/related-data — Mustafa Gursel, Jun 25 '19 at 05:46
We need the code where you're running the query to be able to help — Robert Perry, Jun 25 '19 at 08:03
Hi Guys, looking at the learn.microsoft.com/en-us/ef/core/querying/related-data. The eager loading works great, I will try to figure out why the Lazy Loading doesn't work on my application. Mustafa if you want, put that answer to this question so I can put it answered. — Franz Justin Buenaventura, Jun 25 '19 at 16:32

score 0 · Accepted Answer · answered Jun 26 '19 at 16:44

This answer is actually from Mustafa Gursel on the comments on my post - learn.microsoft.com/en-us/ef/core/querying/related-data

I'm not sure if it is Postgres related or .net core since my experience on .Net MVC 4 with MSSQL is that i don't need to declare lazy loading aside from declaring the "virtual".

In this case I need to install Entity Framework Proxy to make it work without doing Eager Loading.

Unable to implement database model relationships

1 Answers1