如何使用 LINQ 和 EF Core 进行一对多

Question

In my Place Repository I want to bring all the Place records including any Registration records for each Place , even if there are no records in the Registration table.

Currently I have:

public IEnumerable<Place> Places
{
   get
   {
      return _appDbContext.Places.Include(r => r.Registrations.Where(q => q.PlaceId == r.Id));
   }
}

Results in the following error:

InvalidOperationException: The LINQ expression 'DbSet().Where(r => EF.Property(EntityShaperExpression: EntityType: Place ValueBufferExpression: ProjectionBindingExpression: Outer.Outer.Outer.Outer.Outer.Outer.Outer.Outer IsNullable: False, "Id").= null && object:Equals( objA. (object)EF:Property(EntityShaperExpression: EntityType: Place ValueBufferExpression: ProjectionBindingExpression. Outer.Outer.Outer.Outer.Outer.Outer.Outer:Outer IsNullable, False, "Id"): objB. (object)EF,Property(r. "PlaceId"))).Where(r => r.PlaceId == r.Id)' could not be translated, Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList'. or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

The Model:

public class Place
{
   private const int _annualFiguresDueWithinDays = 90;
   public int Id { get; set; }
   [Required(ErrorMessage = "Please enter in the Place's name.")]
   [MaxLength(100, ErrorMessage = "The maximum length for the place name is 100 characters.")]
   public string PlaceName { get; set; }
   public IEnumerable<Registration> Registrations { get; set; }
}

public class Registration
{
   public int Id { get; set; }
   [ForeignKey("PlaceId")]
   public int PlaceId { get; set; }
   public DateTime? RegistrationDate { get; set; }
   public bool IsFirstRegistration { get; set; }
}

Answer 1

Just change the include function to this

public IEnumerable<Place> Places
{
   get
   {
      return _appDbContext.Places.Include(r => r.Registrations));
   }
}