Question

提前致谢！我在获取循环引用时遇到问题，其中EntityA具有EntityB的可空外键，而EntityB具有对EntityA的不可空（强制）引用。我已经创建了一个示例来演示，但我无法通过外键让EntityA引用EntityB：

public class EntityA
{
    public int Id { get; set; }

    public string Name { get; set; }

    public string Description { get; set; }

    public EntityB MasterEntityB { get; set; }

    public int? MasterEntityBId { get; set; }
}

public class EntityB
{
    public string Name { get; set; }

    public int Id { get; set; }

    public EntityA EntityA { get; set; }

    public int AssociationTypeId { get; set; }
}

public class DataContext : DbContext
{
    public DataContext()
        : base("CyclicTest")
    {
    }

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

        modelBuilder.Entity<EntityB>()
            .HasRequired(t => t.EntityA)
            .WithOptional(a => a.MasterEntityB)
            .WillCascadeOnDelete(false);
    }

    public DbSet<EntityB> Tenants { get; set; }

    public DbSet<EntityA> AssociationTypes { get; set; }
}

以下是我的移民：

    public partial class Initial : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.EntityAs",
            c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    Name = c.String(),
                    Description = c.String(),
                    MasterEntityBId = c.Int(),
                })
            .PrimaryKey(t => t.Id);

        CreateTable(
            "dbo.EntityBs",
            c => new
                {
                    Id = c.Int(nullable: false),
                    Name = c.String(),
                    AssociationTypeId = c.Int(nullable: false),
                })
            .PrimaryKey(t => t.Id)
            .ForeignKey("dbo.EntityAs", t => t.Id)
            .Index(t => t.Id);
    }

    public override void Down()
    {
        DropForeignKey("dbo.EntityBs", "Id", "dbo.EntityAs");
        DropIndex("dbo.EntityBs", new[] { "Id" });
        DropTable("dbo.EntityBs");
        DropTable("dbo.EntityAs");
    }
}

我可以手动更改迁移，因此它是一个外键，如下所示：

        CreateTable(
            "dbo.EntityAs",
            c => new
            {
                Id = c.Int(nullable: false, identity: true),
                Name = c.String(),
                Description = c.String(),
                MasterEntityBId = c.Int(),
            })
            .PrimaryKey(t => t.Id)
            .ForeignKey("dbo.EntityBs", t => t.MasterEntityBId);

        CreateTable(
            "dbo.EntityBs",
            c => new
            {
                Id = c.Int(nullable: false, identity: true),
                Name = c.String(),
                EntityAId = c.Int(nullable: false),
            })
            .PrimaryKey(t => t.Id)
            .ForeignKey("dbo.EntityAs", t => t.EntityAId)
            .Index(t => t.Id);

但是当我插入EntityB时，我发现我收到了一个错误：＆＃34;无法在表格中插入明确的标识值＆＃39; EntityB＆＃39;当IDENTITY_INSERT设置为OFF时。＆＃34;

再次感谢帮助！ -max

Answer 1

好的，我发现了问题。我没有通过虚拟馆藏从A到B的一对多参考。这足以解决问题。此外，我已决定使用子类作为主参考，因此我不需要从B返回A的第二个引用作为主实例。对于所有其他实例，这将为null，并且可能导致重复打破MasterB和A之间的0或1对1预期关系。即：

public class EntityA
{
    public int Id { get; set; }

    public string Name { get; set; }

    public string Description { get; set; }

    **public ICollection<EntityB> EntityBs { get; set; }**

    public MasterEntityB MasterEntityB { get; set; }

    public int? MasterEntityBId { get; set; }
}

public class MasterEntityB : EntityB
{
}

public class EntityB
{
    public string Name { get; set; }

    public int Id { get; set; }

    public EntityA EntityA { get; set; }

    public int EntityAId { get; set; }
}

实体代码第一个循环引用迁移

1 个答案: