[英]EF Core 5 - Many to Many - remove
I am using new feature of EF Core 5 where I dont have to specify many-to-many class by myself and instead let it do for EF itself.我正在使用 EF Core 5 的新功能,我不必自己指定多对多 class 而是让它为 EF 本身做。
I have a simple classes:我有一个简单的课程:
UserMap:用户地图:
public class UserMap : IEntityTypeConfiguration<User>
{
public void Configure(EntityTypeBuilder<User> builder)
{
builder.HasKey(x => x.Id);
builder.HasMany(x => x.Favorites).WithMany(x => x.Followers);
}
}
public class RecipeProviderMap : IEntityTypeConfiguration<RecipeProvider>
{
public void Configure(EntityTypeBuilder<RecipeProvider> builder)
{
builder.HasKey(x => x.Id);
builder.HasMany(x => x.Followers).WithMany(x => x.Favorites);
}
}
And of course collections in each class like:当然,每个 class 中的 collections 就像:
public ICollection<User> Followers { get; set; }
public ICollection<RecipeProvider> Favorites { get; set; }
If I want to add an follower to RecipeProvider class I do:如果我想向 RecipeProvider class 添加关注者,我会这样做:
var recipeProvider = await _dataProvider
.RecipeProviders
.Include(x => x.Followers)
.FirstOrDefaultAsync(x => x.Id == request.RecipeProviderId, cancellationToken);
if (recipeProvider == null)
return Unit.Value;
recipeProvider.AddAsFavorite(user);
_dataWriter.Update(recipeProvider);
await _dataWriter.SaveChangesAsync();
Not that line HAS to be added不必添加该行
_dataWriter.Update(recipeProvider);
_dataWriter.Update(recipeProvider);
So above example work for adding but I have problem with removing and I tried a lot of different options.所以上面的示例适用于添加,但我在删除时遇到了问题,我尝试了很多不同的选项。 The proposal looks like:
该提案如下所示:
var user = await
_dataProvider
.Users
.Include(x => x.Favorites)
.FirstOrDefaultAsync(x => x.Id == request.FollowerId, cancellationToken);
var provider = user.Favorites.FirstOrDefault(x => x.Id == request.RecipeProviderId);
user.Favorites.Remove(provider);
await _dataWriter.SaveChangesAsync();
And above code do not remove the entity.上面的代码不会删除实体。 Am I missing something?
我错过了什么吗?
I took your code and made a similar model but with books and tags.我拿了你的代码,做了一个类似的 model 但有书籍和标签。
var tag = dbCotnext.Find<Tag>(1);
var book = dbCotnext.Find<Book>(1);
tag.Books.Add(book);
dbCotnext.SaveChanges();
tag.Books.Remove(book);
dbCotnext.SaveChanges();
I placed breakpoints after both SaveChanges and everything in the database looked as expected, I see the new entity in the BookTag table after hitting the first breakpoint and it vanishes after I hit the second.我在 SaveChanges 和数据库中的所有内容都按预期放置之后放置了断点,我在击中第一个断点后看到 BookTag 表中的新实体,在我击中第二个断点后它消失了。
However, I see something alerting in your code.但是,我在您的代码中看到了一些警告。 You're using two contexts, one for reads
_dataProvider
and the other for writes _dataWriter
.您正在使用两种上下文,一种用于读取
_dataProvider
,另一种用于写入_dataWriter
。 I think that if you would call SaveChanges
on the _dataProvider
it would work, but you call it on _dataWriter
where the entity you loaded from the other context is not tracked.我认为,如果您在
_dataProvider
上调用SaveChanges
它将起作用,但是您在_dataWriter
上调用它,您从其他上下文加载的实体不会被跟踪。 You could explicitly load it to _dataWriter
and then remove the element from the collection and then save changes, so then SaveChanges
would work as expected on the _dataWriter
.您可以将其显式加载到
_dataWriter
,然后从集合中删除该元素,然后保存更改,这样SaveChanges
将在_dataWriter
上按预期工作。
To sum up, I think that _dataWriter
is not tracking changes on the entity loaded by another context which is _dataProvider
.总而言之,我认为
_dataWriter
没有跟踪由另一个上下文加载的实体的更改,即_dataProvider
。
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