如何使用 LINQ 和 EF Core 实现一对多

Question

在我的 Place Repository 中，我想带来所有 Place 记录，包括每个 Place 的任何 Registration 记录，即使有Registration table.

中没有记录

目前我有：

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

导致以下错误：

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.

模特：

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

把include函数改成这样就可以了

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