实体框架6：代码优先级联删除

问题描述

因此​​，有在这里这几天类似的问题，但我仍然有问题determing正是我缺少我的情况简化什么。

So there are several similar questions on here to this, but I'm still having issues determing what exactly I'm missing in my simplified scenario.

让我们说我有以下表中，巧妙地命名后的自己：

Let's say I have the following tables, cleverly named after myself:

'JohnsParentTable' (Id, Description)
'JohnsChildTable' (Id, JohnsParentTableId, Description)

通过生成的类看起来像这样

With the resulting classes looking like so

public class JohnsParentTable
{
    public int Id { get; set; }
    public string Description { get; set; }
    public virtual ICollection<JohnsChildTable> JohnsChildTable { get; set; }

    public JohnsParentTable()
    {
        JohnsChildTable = new List<JohnsChildTable>();
    }
}

internal class JohnsParentTableConfiguration : EntityTypeConfiguration<JohnsParentTable>
{
    public JohnsParentTableConfiguration()
    {
        ToTable("dbo.JohnsParentTable");
        HasKey(x => x.Id);
        Property(x => x.Id).HasColumnName("Id").IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        Property(x => x.Description).HasColumnName("Description").IsRequired().HasMaxLength(50);
    }
}

public class JohnsChildTable
{
    public int Id { get; set; }
    public string Description { get; set; }
    public int JohnsParentTableId { get; set; }
    public JohnsParentTable JohnsParentTable { get; set; }
}

internal class JohnsChildTableConfiguration : EntityTypeConfiguration<JohnsChildTable>
{
    public JohnsChildTableConfiguration()
    {
        ToTable("dbo.JohnsChildTable");
        HasKey(x => x.Id);
        Property(x => x.Id).HasColumnName("Id").IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        Property(x => x.Description).HasColumnName("Description").IsRequired().HasMaxLength(50);
        HasRequired(a => a.JohnsParentTable).WithMany(c => c.JohnsChildTable).HasForeignKey(a => a.JohnsParentTableId);
    }
}

在数据库中，我有父表中的行与1与连接到这个父子表两行沿标识。如果我这样做：

In the database I have a row in the parent table with an Id of 1 along with two rows in the child table tied to this parent. If I do this:

var parent = db.JohnsParentTable.FirstOrDefault(a => a.Id == 1)

对象正确填充。但是，如果我尝试删除该行：

The object is correctly populated. However, if I try to delete this row:

var parent = new Data.Models.JohnsParentTable() { Id = 1 };
db.JohnsParentTable.Attach(parent);
db.JohnsParentTable.Remove(parent);

db.SaveChanges();

实体框架尝试执行以下操作：

Entity framework tries to execute the following:

DELETE [dbo].[JohnsParentTable]
WHERE ([Id] = @0)
-- @0: '1' (Type = Int32)
-- Executing at 1/23/2014 10:34:01 AM -06:00
-- Failed in 103 ms with error: The DELETE statement conflicted with the REFERENCE constraint "FK_JohnsChildTable_JohnsParentTable". The conflict occurred in database "mydatabase", table "dbo.JohnsChildTable", column 'JohnsParentTableId'.
The statement has been terminated.

我的问题则是，究竟我缺少保证实体框架知道它必须删除JohnsChildTable 删除父前行？

My question then is what exactly am I missing to ensure Entity Framework knows that it must delete the 'JohnsChildTable' rows before deleting the parent?

推荐答案

这取决于你是否希望实体框架删除的孩子，或者你希望数据库要照顾它。

It depends on whether you want Entity Framework to delete the children, or you want the database to take care of it.

如果你想EF生成所有的孩子一个delete语句，并删除父之前执行的，必须所有的孩子装入内存第一。

If you want EF to generate a delete statement for all the children and execute those before deleting the parent, you have to load all the children into memory first.

所以你不能简单地创建只填充的关键是虚拟实体，并期望孩子被删除。

So you can't simply create a "dummy" entity with just the key populated, and expect the children to be deleted.

有关的工作，你必须让数据库处理删除。

For that to work, you have to let the database handle the deletion.

在子表的外键就必须有但级联删除功能。如果是这样的情况下，实体框架只是创建父DELETE语句，并且数据库知道要删除的孩子们。

The foreign key on the child table would have to have cascade deletes enabled however. If that's the case, Entity Framework just creates a delete statement for the parent, and the database knows to delete the children as well.

实体框架将创建级联外键将删除默认你的情况允许，如果需要的关系，等等。 （外键不能为空）。

Entity Framework creates a foreign key with cascade deletes enabled by default, if the relationship is required, like in your case. (Foreign key can't be null).

如果你自己已经创建了数据库，你要记住启用它。

If you have created the database yourself, you have to remember to enable it.

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