子类的唯一实体框架

Question

我对如何在Entity Framework中处理这种情况感到困惑.

我有一个角色基类:

public class Character
{
    [Key]
    public Guid Id { get; set; }
    public Realm Realm { get; set; }
    public Guid RealmId { get; set; }
    public string Name { get; set; }
}

角色有名称并且必然属于领域.

由玩家控制的角色绝对是一个角色.它与玩家/用户绑定:

public class PlayerCharacter : Character
{        
    public User User { get; set; }
    public Guid UserId { get; set; }
}

NPC也是一个角色:它不需要具有MCVE的任何属性

public class Npc : Character { }

现在,显然,您不希望在同一领域中使用相同名称的字符,但是您可以Orcs在单个领域中拥有所需数量,因此我们需要定义唯一约束PlayerCharacter,例如通过.HasAlternateKey:

public DbSet<PlayerCharacter> Characters { get; set; }
public DbSet<Npc> Npcs { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.Entity<PlayerCharacter>()
        .HasAlternateKey("Name", "RealmId");
}

现在我们添加迁移:

$ dotnet ef migrations add 5
System.InvalidOperationException: A key cannot be configured on 
'PlayerCharacter' because it is a derived type. The key must be 
configured on the root type 'Character'.

好的,一个独特的索引怎么样？

modelBuilder.Entity<PlayerCharacter>()
    .HasIndex("Name", "RealmId")
    .IsUnique();

$ dotnet ef migrations add 5
Done. To undo this action, use 'ef migrations remove'

有效!可是等等:

migrationBuilder.CreateTable(
    name: "Character",
    columns: table => new
    {
        Id = table.Column<Guid>(nullable: false),
        Discriminator = table.Column<string>(nullable: false),
        Name = table.Column<string>(nullable: true),
        RealmId = table.Column<Guid>(nullable: false),
        // other props...
    },
    constraints: table =>
    {
        table.PrimaryKey("PK_Character", x => x.Id);
        // foreign keys...
    });

migrationBuilder.CreateIndex(
    name: "IX_Character_Name_RealmId",
    table: "Character",
    columns: new[] { "Name", "RealmId" },
    unique: true);

现在玩家角色和npcs都是名字独一无二的!如何仅在派生类中设置唯一？

Answer 1

当前可以执行此操作的唯一方法(EF Core 2.0.1)是使用基于Discriminator列值的筛选唯一索引.

不幸的是,HasFilter流畅的API不是db不可知的.这是SqlServer的配置:

modelBuilder.Entity<PlayerCharacter>()
    .HasIndex("Name", "RealmId")
    .IsUnique()
    .HasFilter("Discriminator = 'PlayerCharacter'"); // <--