How to query many-to-many releationship in EF Core

Question

I'm using .NET Core and EF Core for a web project. I'm struggling how to query a many-to-many releationship. This is what my models look like:

public class Begrip {     public int ID { get; set; }     public string Name { get; set; }      public string Desc { get; set; }     [Url]     public string URL { get; set; }      public ICollection<BegripCategory> Categories { get; set; }  }  public class Category {     public int ID { get; set; }     public string Name { get; set; }      public ICollection<BegripCategory> Begrippen { get; set; } }  public class BegripCategory {     public int begripId { get; set; }     public Begrip begrip { get; set; }      public int categoryId { get; set; }     public Category category { get; set; }  } 

And my Database context:

public class PBBContext : DbContext {     public PBBContext (DbContextOptions<PBBContext> options)         : base(options)     {     }      public DbSet<PBB.Models.Movie> Movie { get; set; }     public DbSet<PBB.Models.Begrip> Begrip { get; set; }      public DbSet<PBB.Models.Category> Category { get; set; }      public DbSet<PBB.Models.BegripCategory> BegripCategory { get; set; }      protected override void OnModelCreating(ModelBuilder modelbuilder)     {         modelbuilder.Entity<BegripCategory>().HasKey(bc => new { bc.begripId, bc.categoryId });          modelbuilder.Entity<BegripCategory>().HasOne(b => b.begrip).WithMany(bg => bg.Categories).HasForeignKey(bc => bc.begripId);         modelbuilder.Entity<BegripCategory>().HasOne(c => c.category).WithMany(ca => ca.Begrippen).HasForeignKey(cc => cc.categoryId);     } } 

What im trying to do is to return all the "Begrippen" in a JSON result with all the corresponding "Categories", however, I can't figure out how to get the list of "Categories" for them.

Any ideas? Thanks in advance.

Answer 1

EF Core won't load related properties automatically, so you'll need to explicitly do this, but something like the following should do the trick:

var result = context.Begrip     .Include(x => x.Categories)     .ThenInclude(x => x.category); 

Note, intellisense doesn't always work on .ThenInclude at the moment, but the code should still compile even if it gets a red underline.

If you're returning this to the view or an API, you'll likely want to map it to a DTO so you don't have to deal with .Categories[0].category.Name etc.