Question

我有一个使用数据库优先模型的WEB API项目。我有基类Building实体和MultiApartmentBuilding实体，它们是从Building继承的。我还有一个Apartment实体，它与Building实体以一对多的关系连接。我想通过给定的公寓ID获取特定的公寓，并提供一些MultiApartmentBuilding信息。

到目前为止，我已经尝试通过Include() LINQ方法获得理想的结果，但是遇到一个我不能包含MultiapartmentBuilding的问题。

这是我的Building班。

public abstract class Building
{
    public int Id { get; set; }
    public BuildingState State { get; set; }
    public BuildingType Type { get; set; }
    public int AddressId { get; set; }
    public Address Address { get; set; }
    public MultilingualString Description { get; set; }
    public string MainImg { get; set; }
    public bool IsBuilt { get; set; }
}

这是我的MultiApartmentBuilding班。

public class MultiApartmentBuilding : Building
{
    public int GroundFloorCount { get; set; }
    public double FloorHeight { get; set; }
    public int? WallId { get; set; }
    public Wall Wall { get; set; }       
}

这是我的Apartment班。

public class Apartment : EntityBase
{
    public int Id { get; set; }

    public int BuildingId { get; set; }
    public Building Building { get; set; }
    public Common.Enums.ApartmentState State { get; set; }
    public AccessibilityState Accessibility { get; set; }
    public int Floor { get; set; }
    public bool IsPentHouse { get; set; }
}

这是我的LINQ查询，应该返回单元。

var apartment = _context.Apartments
    .Where(id => id.Id == apartmentId)
    .Include(building => building.Building)
        .ThenInclude(address => address.Address)
        .ThenInclude(city => city.City)
        .ThenInclude(cityName => cityName.Name)
   .Include(district => district.Building.Address.District)
        .ThenInclude(districtName => districtName.Name)
   .Include(street => street.Building.Address.Street)
   .Include(condPrices => condPrices.ConditionPrices)
        .ThenInclude(condition => condition.Condition)
        .ThenInclude(conditionName => conditionName.Name)
        .ThenInclude(conditionNameTranslation => conditionNameTranslation.Translations)
   .Include(builder => builder.Building.Builder)
        .ThenInclude(brandName => brandName.BrandName)
        .ThenInclude(brandNameTrans => brandNameTrans.Translations)
    .Include(builderBussinesAddress => builderBussinesAddress.Building.Builder.BusinessAddress)
         .ThenInclude(tranlsations => tranlsations.Translations)
   .Include(descriptipon => descriptipon.Description)
        .ThenInclude(descriptionName => descriptionName.Translations)

此查询的问题是我无法访问MultiApartmentBuilding字段。尽管Building是从MultiApartmentBuilding继承的，但是我只能访问Building字段。有没有办法也可以访问MultiApartmenBuilding字段？

Answer 1

包含Building还将包括MultiApartmentBuilding个条目（实际上，所有类型都源自Building）。

您可以使用C＃7.0的模式匹配来同时测试和投射（其中apartments是查询的结果）：

foreach (Apartment apartment in apartments) {
    // Access common Building field.
    Console.WriteLine(apartment.Building.Id);

    // Access specialized field from derived building type.
    if (apartment.Building is MultiApartmentBuilding maBuilding) {
        Console.WriteLine(maBuilding.GroundFloorCount);
    }
}

如果建筑物类型很多，则可以在switch语句中使用模式匹配

switch (apartment.Building)
{
    case MultiApartmentBuilding maBuilding:
        Console.WriteLine(maBuilding.GroundFloorCount);
        break;
    case Igloo igloo:
        Console.WriteLine(igloo.SnowQuality);
        break;
    default:
        Console.WriteLine("all other building types");
        break;
}

Answer 2

您尝试过投射吗？

var multiApartments = (MultiApartmentBuilding)apartment.Building;

Answer 3

您无法访问孩子的班级属性。换句话说，如果您拥有建筑物，则无法访问其 MultiApartmentBuilding 属性，因为您甚至不知道它是否真的是 MultiApartmentBuilding 。在这种情况下，我要做的就是更改您的 Apartment 类，并使用 MultiApartmentBuilding 类型而不是 Building ：

public class Apartment : EntityBase
{
    public int Id { get; set; }

    public int BuildingId { get; set; }
    public MultiApartmentBuilding MultiApartmentBuilding { get; set; }
    public Common.Enums.ApartmentState State { get; set; }
    public AccessibilityState Accessibility { get; set; }
    public int Floor { get; set; }
    public bool IsPentHouse { get; set; }
 }

LINQ包含和继承

3 个答案: