C# 如何在EF代码第一数据库中删除子一对多相关记录？
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How to remove child one to many related records in EF code first database?
提问by Dmytro
Well, I have one-to-many related model:
好吧，我有一对多的相关模型：
public class Parent
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Child> Children { get; set; }
}
public class Child
{
public int Id { get; set; }
public string ChildName { get; set; }
}
What I want to do is clear Parent.Childrenand remove related child entities from database. I've already tried:
我想要做的是清除Parent.Children并从数据库中删除相关的子实体。我已经试过了：
Database context class:
数据库上下文类：
modelBuilder.Entity<Parent>()
.HasMany(p => p.Children)
.WithOptional()
.WillCascadeOnDelete(true);
this works fine, but I still have redundant records in database with Parent_Id = nullfields when I do
这工作正常，但是Parent_Id = null当我这样做时，我在带有字段的数据库中仍然有冗余记录
parent.Children.Clear();
repository.InsertOrUpdate(parent);
in my repository class. Also the same behavior is when I do:
在我的存储库类中。同样的行为是当我这样做时：
modelBuilder.Entity<Parent>()
.HasMany(pr => pr.Children)
.WithOptional(ri => ri.Parent)
.WillCascadeOnDelete(true);
with additional Parentproperty in Childclass
Parent在Child课堂上有额外的财产
public class Child
{
...
public Parent Parent { get; set; }
...
}
or when I do
或者当我做
modelBuilder.Entity<Child>()
.HasOptional(p => p.Parent)
.WithMany(p => p.Children)
.HasForeignKey(p => p.Parent_Id)
.WillCascadeOnDelete(true);
with additional Parent_Id property in Childclass
在Child课堂上有额外的 Parent_Id 属性
public class Child
{
...
public int Parent_Id { get; set; }
...
}
So, how can I configure cascade deleting correctly? Or how should I supposed to remove those child entities? I assume this is casual task but I'm just missing something.
那么，如何正确配置级联删除呢？或者我应该如何删除这些子实体？我认为这是一项随意的任务，但我只是错过了一些东西。
采纳答案by Slauma
Cascading delete has no effect here because you don't delete the parentbut just call InsertOrUpdate. The correct procedure is to delete the children one-by-one, like so for example:
级联删除在这里不起作用，因为您不删除parent而是调用InsertOrUpdate. 正确的过程是一个一个地删除孩子，例如：
using (var context = new MyContext())
{
var parent = context.Parents.Include(p => p.Children)
.SingleOrDefault(p => p.Id == parentId);
foreach (var child in parent.Children.ToList())
context.Children.Remove(child);
context.SaveChanges();
}
回答by Kirsten Greed
Try changing to
尝试更改为
public virtual ICollection<Child> Children { get; set; }
because virtual is needed to get lazy loading. as explained here
因为需要 virtual 才能获得延迟加载。为解释 在这里
I think your parent.Children.clear isnt working because the Children have not been loaded
我认为您的 parent.Children.clear 不起作用，因为 Children 尚未加载
回答by Sam Sippe
In EF6 a faster way to do the operation is...
在 EF6 中，一种更快的操作方法是......
context.Children.RemoveRange(parent.Children)
回答by Matthew Hudson
If your object is self-referencing, you can delete both many-to-many and one-to-many children using the method below. Just remember to call db.SaveChanges() afterwards :)
如果您的对象是自引用的，您可以使用以下方法删除多对多和一对多子项。请记住之后调用 db.SaveChanges() :)
[HttpPost, ActionName("Delete")]
[ValidateAntiForgeryToken]
public ActionResult DeleteConfirmed(int id)
{
Object obj = this.db.Objects.Find(id);
this.DeleteObjectAndChildren(obj);
this.db.Objects.Remove(obj);
this.db.SaveChanges();
return this.Json(new { success = true });
}
/// <summary>
/// This deletes an object and all children, but does not commit changes to the db.
/// - MH @ 2016/08/15 14:42
/// </summary>
/// <param name="parent">
/// The object.
/// </param>
private void DeleteObjectAndChildren(Object parent)
{
// Deletes One-to-Many Children
if (parent.Things != null && parent.Things.Count > 0)
{
this.db.Things.RemoveRange(parent.Things);
}
// Deletes Self Referenced Children
if (parent.Children != null && parent.Children.Count > 0)
{
foreach (var child in parent.Children)
{
this.DeleteObjectAndChildren(child);
}
this.db.Objects.RemoveRange(parent.Children);
}
}
回答by Konrad
This is called "deleting orphans".
这称为“删除孤儿”。
Can EF automatically delete data that is orphaned, where the parent is not deleted?
I don't know how it works in EF6 but in EF Core it works fine https://docs.microsoft.com/en-us/ef/core/saving/cascade-deleteso you don't necessarily need to delete the parent for cascades to work.
我不知道它在 EF6 中是如何工作的，但在 EF Core 中它工作正常https://docs.microsoft.com/en-us/ef/core/saving/cascade-delete所以你不一定需要删除级联工作的父级。
