由网友(情深致命)分享简介：使用实体框架code-第一的方针。Using Entity Framework code-first approach.假设我有两个实体类：[Table("Objects")]public class DbObject : IValidatableObject{public long Id { get; se...

使用实体框架code-第一的方针。

Using Entity Framework code-first approach.

假设我有两个实体类：

[Table("Objects")]
public class DbObject : IValidatableObject
{
    public long Id { get; set; }

    public string Name { get; set; }
    public string Description { get; set; }

    public virtual ICollection<DbObjectProperty> Properties { get; set; }
}

[Table("ObjectProperties")]
public class DbObjectProperty
{
    public long Id { get; set; }

    public string Name { get; set; }
    public string Value { get; set; }

    [Display(Name = "Object"), UIHint("Object")]
    public long ObjectId { get; set; }
    public virtual DbObject Object { get; set; }
}

要点，这里要注意：

Points to note here:

DBOBJECT 只有一个导航属性​​，但与外键的任何一列 DbObjectProperty 有一个导航属性​​的和的一个外键对应的列 这应该是显而易见的是，如果我删除一个对象，我想它的属性去用它，但如果我删除一个单一的财产，我不想消失，整个对象。 DbObject only has a navigation property, but no column with a foreign key DbObjectProperty has a navigation property and a corresponding column with a foreign key It should be obvious that if I delete an object, I want its properties to go with it, but if I delete a single property, I don’t want the entire object to disappear.

在 OnModelCreating 法为DB的背景下，到现在为止，我有以下定义的关系：

In the OnModelCreating method for the DB context, up until now I had the following to define the relationship:

modelBuilder.Entity<DbObjectProperty>()
    .HasRequired(op => op.Object)
    .WithMany(obj => obj.Properties)
    .HasForeignKey(op => op.ObjectId)
    .WillCascadeOnDelete(false);

当然，

，这意味着没有级联会出现删除。我的问题是：如果我更改为真，这是否做我想要什么？请记住，如果我删除一个对象，我想它的属性去用它，但如果我删除一个单一的财产，我不想消失，整个对象。

Of course, this means no cascaded deletes will occur. My question is: if I change this to true, does that do what I want? Remember if I delete an object, I want its properties to go with it, but if I delete a single property, I don’t want the entire object to disappear.

自动生成的迁移code为这种变化（从假到真）是这样的：

The auto-generated migration code for this change (from false to true) is this:

DropForeignKey("ObjectProperties", "ObjectId", "Objects");
DropIndex("ObjectProperties", new[] { "ObjectId" });
AddForeignKey("ObjectProperties", "ObjectId", "Objects", "Id", cascadeDelete: true);
CreateIndex("ObjectProperties", "ObjectId");

我很担心，这似乎意味着，删除属性将删除其关联的对象。会吗？

I am worried that this seems to imply that deleting a property will delete its associated object. Will it?

推荐答案

级联的方向的数据库中的关系删除是由什么是主要的（主表/唯一密钥）来定义，什么是相关的（表这种关系的外键）的。

The direction of Cascading Delete of a relationship in the database is defined by what is the principal (table of the primary/unique key) and what is the dependent (table of the foreign key) of this relationship.

然后，如果你删除它具有对应于主体的主/唯一键值的外键值的所有家属都将被删除，以及校长。有一个从依赖的方向没有级联删除本金。

Then, if you delete the principal all dependents which have a foreign key value corresponding to the primary/unique key value of that principal are deleted as well. There is no cascading delete in the direction from dependent to principal.

在你的情况主要是 DBOBJECT 和相关的 DbObjectProperty ，因为它是实体/表与外键。

In your case the principal is DbObject and the dependent is DbObjectProperty because it is the entity/table with the foreign key.

这将很少有意义有级联删除周围的其他方法 - 尤其是在x一对多的关系：如果删除的依赖（ DbObjectProperty ）和委托人（ DBOBJECT ）将被自动删除，如果有任何其他的依赖。参见主要是将要删除的外键约束会被侵犯。

It would rarely make sense to have a cascading delete the other way around - especially in x-to-many relationships: If you delete a dependent (DbObjectProperty) and the principal (DbObject) would be deleted automatically, a foreign key constraint would be violated if there is any other dependent refering to the principal which is going to be deleted.

您不必担心。