Question

我刚开始使用Code first方法来创建数据库。我有以下3个表：

public class TagDatabase
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int TagID { get; set; }
    public string TagName { get; set; }
    public string Description { get; set; }
    public int Count { get; set; }

    [ForeignKey("TagTypes")]
    public virtual int TagTypeID { get; set; }
    public virtual ICollection<TagTypesDb> TagTypes { get; set; }

    [ForeignKey("Users")]
    public virtual int CreatedBy { get; set; }
    public virtual UsersDb Users { get; set; }
}

public class TagTypesDb
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int TagTypeID { get; set; }
    public string TagTypeName { get; set; }
}

public class UsersDb
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int UserID { get; set; }
    public string UserName { get; set; }
}

这里TagDatabse和User和TagType有1对1的重播。我用于此的流畅API代码是：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<TagDatabase>()
           .HasOptional(a => a.TagTypes)
           .WithMany()
           .HasForeignKey(u => u.TagTypeID);

        modelBuilder.Entity<TagDatabase>()
                    .HasRequired(a => a.Users)
                    .WithMany()
                    .HasForeignKey(u => u.CreatedBy);
}

现在我的问题是每当我尝试在TagDatabase中插入数据时，我都遇到了这个例外：

TagDatabase_TagTypes: : Multiplicity conflicts with the referential constraint in Role 'TagDatabase_TagTypes_Target' in relationship 'TagDatabase_TagTypes'. Because all of the properties in the Dependent Role are non-nullable, multiplicity of the Principal Role must be '1'.

TagTypeId属性允许为null。因此我在OnModelCreating方法中使用了HasOptional（）。

Cananybody请告诉我如何解决这个问题以及我在这里缺少什么？

Answer 1

如果对应关系是可选的，则应该创建外键属性nullable。

public class TagDatabase
{
  //sniff...

 [ForeignKey("TagTypes")]
 public virtual int? TagTypeID { get; set; }      //Since TagTypes is optional, this should be nullable
 public virtual ICollection<TagTypesDb> TagTypes { get; set; }

 //sniff...
}

代码优先INSERT语句与FOREIGN KEY约束冲突

1 个答案: