在实体框架中的抽象类上配置自动增量字段

Question

我有一些类似于这些的代码优先实体：

public abstract class Animal {
    public int ID { get; set; }
    public int NumberOfLegs { get; set; }
}

public class Dog : Animal {
    public string OtherDogRelatedStuff { get; set; }
}

public class Bird : Animal {
    public string OtherBirdRelatedStuff { get; set; }
}

public class MyContext : DbContext {

    public IDbSet<Animal> Animals { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder) {

        var pluraliser = PluralizationService.CreateService(new System.Globalization.CultureInfo("en-GB"));

        modelBuilder.HasDefaultSchema("vs");
        modelBuilder.Types().Configure(t => t.ToTable(pluraliser.Pluralize(t.ClrType.Name)));

        // This next line doesn't give ID column IDENTITY(1,1)
        modelBuilder.Entity<Animal>().Property(_ => _.ID).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        // This line puts IDENTITY(1,1) on Animal.ID, but causes errors when I try to add/update data.
        //modelBuilder.Entity<Dog>().Property(_ => _.ID).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        base.OnModelCreating(modelBuilder);
    }        
}

我想要每种类型的表格......所以表格看起来像这样：

CREATE TABLE Animals (
    ID INT NOT NULL IDENTITY(1,1),
    NumberOfLegs INT NOT NULL,
    CONSTRAINT pkAnimals PRIMARY KEY (ID)
)

CREATE TABLE Dogs (
    ID INT NOT NULL,
    OtherDogRelatedStuff VARCHAR(200),
    CONSTRAINT pkDogs PRIMARY KEY (ID),
    CONSTRAINT fkAnimal_Dog FOREIGN KEY (ID) REFERENCES Animals(ID)
)

CREATE TABLE Birds (
    ID INT NOT NULL,
    OtherBirdRelatedStuff VARCHAR(200),
    CONSTRAINT pkBirds PRIMARY KEY (ID),
    CONSTRAINT fkAnimal_Bird FOREIGN KEY (ID) REFERENCES Animals(ID)
)

数据看起来像这样：

---Animals----------
ID      NumberOfLegs
1       4
2       4
3       2

---Dogs---------------------
ID      OtherDogRelatedStuff
1       Woof1
2       Woof2

---Birds---------------------
ID      OtherCatRelatedStuff
3       Sqwark1

但我无法让自动增量 ID 正常工作或配置正确。

我试过了：

modelBuilder.Entity<Animal>().Property(_ => _.ID)
    .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

但是因为Animal 是抽象的，这似乎没有在表格上设置IDENTITY(1,1) 属性。

我也尝试在 Dog 实体上执行相同的操作，它正确地将标识属性添加到 Animals 表中的 ID 列，但是当我尝试将新实体添加到SaveChanges() 方法上的数据库：

A dependent property in a ReferentialConstraint is mapped to a store-generated column. Column: 'ID'.

如何正确地将抽象类型上的 ID 列设置为自动递增，并使其在添加数据时起作用？

Answer 1

我会说使用接口或单独的抽象类来放置这样的常见功能：

public interface Common{
  int ID { get; set; }
}
public class Animal : Common {
[DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]    
public int ID { get; set; }
public int NumberOfLegs { get; set; }
}

public class Dog : Common {
    public int ID { get; set; }
    public string OtherDogRelatedStuff { get; set; }
}

Answer 2

有了这些模型...

public abstract class Animal
{
    public int ID { get; set; }
    public int NumberOfLegs { get; set; }
}

public class Dog : Animal
{
    public string OtherDogRelatedStuff { get; set; }
}

public class Bird : Animal
{
    public string OtherBirdRelatedStuff { get; set; }
}

...在上下文中...

public IDbSet<Animal> Animals { get; set; }

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);
    modelBuilder.Entity<Dog>().ToTable("Dogs");
    modelBuilder.Entity<Bird>().ToTable("Birds");
}

...然后在包管理器中执行Add-Migration "Animals" 然后Update-Database -Script

你应该得到：

CREATE TABLE [dbo].[Animals] (
    [ID] [int] NOT NULL IDENTITY,
    [NumberOfLegs] [int] NOT NULL,
    CONSTRAINT [PK_dbo.Animals] PRIMARY KEY ([ID])
)
CREATE TABLE [dbo].[Dogs] (
    [ID] [int] NOT NULL,
    [OtherDogRelatedStuff] [nvarchar](max),
    CONSTRAINT [PK_dbo.Dogs] PRIMARY KEY ([ID])
)
CREATE INDEX [IX_ID] ON [dbo].[Dogs]([ID])
CREATE TABLE [dbo].[Birds] (
    [ID] [int] NOT NULL,
    [OtherBirdRelatedStuff] [nvarchar](max),
    CONSTRAINT [PK_dbo.Birds] PRIMARY KEY ([ID])
)
CREATE INDEX [IX_ID] ON [dbo].[Birds]([ID])
ALTER TABLE [dbo].[Dogs] 
ADD CONSTRAINT [FK_dbo.Dogs_dbo.Animals_ID] FOREIGN KEY ([ID]) 
REFERENCES [dbo].[Animals] ([ID])
ALTER TABLE [dbo].[Birds] 
ADD CONSTRAINT [FK_dbo.Birds_dbo.Animals_ID] FOREIGN KEY ([ID]) 
REFERENCES [dbo].[Animals] ([ID])
INSERT [dbo].[__MigrationHistory]([MigrationId], [ContextKey], [Model], [ProductVersion])
VALUES (N'etc)

这是你想要的，对吧？

参考： Inheritance with EF Code First: Part 2 – Table per Type (TPT)

请注意，如果最初创建的字段没有标识，则使用标识创建的字段有时可能会遇到问题（反之亦然）。您可以通过删除并重新创建表来解决此问题：https://stackoverflow.com/a/18917348/150342

Answer 3

我遇到了同样的问题，我在抽象类中使用数据注释修复了它，如下所示：

public abstract class Animal {
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ID { get; set; }
    public int NumberOfLegs { get; set; }
}