[英]Trying to understand deleting children entities in Entity Framework
我试图理解为什么实体框架以删除子实体的方式工作!
我有一个YogaSpace
对象/实体和一个称为YogaSpaceImage
。 我想从YogaSpace
删除一个YogaSpaceImage
,所以这是我要做的。
这不起作用
yogaSpace.Images.Remove(yogaSpaceImage);
删除子实体!
public string RemoveImage(int id, int imageIdToDelete)
{
YogaSpace yogaSpace = _yogaSpaceRepository.Find(id);
// delete image
foreach (YogaSpaceImage yogaSpaceImage in yogaSpace.Images.OrderBy(m => m.Ordering))
{
if (yogaSpaceImage.YogaSpaceImageId == imageIdToDelete)
{
// check first to see if the deleted image is the first (primary) image, then make the 2nd image the yogaspace thumbnail
if (yogaSpaceImage.Ordering == 1)
{
yogaSpace.SpaceThumbnail = yogaSpace.Images.First(m => m.Ordering == 2).ImageThumbnail;
}
yogaSpace.Images.Remove(yogaSpaceImage);
}
}
}
myRepository.InsertOrUpdate(YogaSpace);
myRepository.Save()
}
当我调用myRepo.Removed(YogaSpaceImage)
时,这确实起作用。
public string RemoveImage(int id, int imageIdToDelete)
{
YogaSpace yogaSpace = _yogaSpaceRepository.Find(id);
// delete image
foreach (YogaSpaceImage yogaSpaceImage in yogaSpace.Images.OrderBy(m => m.Ordering))
{
if (yogaSpaceImage.YogaSpaceImageId == imageIdToDelete)
{
// check first to see if the deleted image is the first (primary) image, then make the 2nd image the yogaspace thumbnail
if (yogaSpaceImage.Ordering == 1)
{
yogaSpace.SpaceThumbnail = yogaSpace.Images.First(m => m.Ordering == 2).ImageThumbnail;
}
_yogaSpaceRepository.Removed(yogaSpaceImage);
}
}
}
myRepository.Save()
}
这是我的Removed()
和InsertOrUpdate()
样子。
public void InsertOrUpdate(YogaSpace yogaSpace)
{
if (yogaSpace.YogaSpaceId == default(int))
{
context.Entry(yogaSpace).State = System.Data.Entity.EntityState.Added;
}
else
{
context.Entry(yogaSpace).State = System.Data.Entity.EntityState.Modified;
}
}
public void Removed(YogaSpaceImage yogaSpaceImage)
{
context.Entry(yogaSpaceImage).State = EntityState.Deleted;
}
PS,您会认为我的回购中的InsetOrUpdate()
对于EntityState.Modified
可以删除子实体吗?
PPS不知道为什么我什至需要InsertOrUpdate()
,它是使用自动生成的nuget包构建的。 如果我不使用它,而只是调用Save()
,那么Entity Framework会理解我所做的更改,因此为什么会为我生成此提示,为什么因为要保存实体,所以entity.Added
和entity.Modified
甚至存在和修改,即使我没有明确调用这两个?
一个不错的小技巧是在孩子的主键中使用父母的ID:
public class Parent
{
public int Id { get; set; }
public virtual List<Child> Children { get; set; }
}
public class Child
{
public int Id { get; set; }
public int ParentId { get; set;}
}
并配置:
modelBuilder.Entity<Parent>()
.HasMany(x => x.Children)
.WithRequired()
.HasForeignKey(x => x.ParentId);
modelBuilder.Entity<Child>()
.HasKey(x => new { x.Id, x.ParentId})
.Property(x => x.Id)
.HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
这样,当您从父级中删除子级时,ParentId不能为空,并且EF会将其标记为要删除。
示例如何向父级添加/删除子级:
using(var db = new DbContext())
{
var p = db.Parents.First();
var c = new Child();
p.Children.Add(c);
db.SaveChanges(); // Child was saved to the database
p.Children.Remove(c);
db.SaveChanges(); // Child will be deleted from the database
p.Children.Clear();
db.SaveChanges(); // All Child of this parent will be deleted
}
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