如何使用 LINQ 和 EF Core 进行一对多

Question

在我的Place Repository中，即使Registration 表中没有记录，我也想为每个Place 带来所有Place 记录，包括任何Registration 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: LINQ 表达式 '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)' 无法翻译。以可翻译的形式重写查询，或通过插入对“AsEnumerable”、“AsAsyncEnumerable”、“ToList”或“ToListAsync”的调用显式切换到客户端评估。请参阅https://go.microsoft.com/fwlink/?linkid=2101038 了解更多信息。

模型：

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函数改成这个就行了

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