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.
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.
If you need to filter a Many-to-Many relationship describe below I recomend to use a LinQ Enumerable Any method like this:
return result.Where(x => x.Categories.Any(c => c.category == categoryId));
To return a filtered list of entities related by a specific category.