是否可以将EF Core 5.0中的多对多关系配置为仅保留一个导航属性(在一侧)? [英] Can many-to-many relationships in EF Core 5.0 be configured keeping just one navigation property (on one side)?

问题描述

我已使用以下代码配置了DbContext(EF Core 5.0):

 受保护的重写void OnModelCreating(ModelBuilder modelBuilder){modelBuilder.Entity< User>().HasMany(p => p.Roles).WithMany(p => p.Users).UsingEntity< Dictionary< string，object>(``UsersToRoles''，x =>x.HasOne< Role>().WithMany().HasForeignKey("UserId")，x =>x.HasOne< User>().WithMany().HasForeignKey("UserId")，x =>x.ToTable("UsersToRoles"))；modelBuilder.Entity< Role>().ToTable(角色").Property(r => r.Application).是必须的();base.OnModelCreating(modelBuilder);} 

问题是我不希望 Role 实体保存 Users 的集合.我保留它是因为EF Core要求它配置多对多关系.

是否可以创建相同的关系，而不必定义 Role.Users 导航属性?

解决方案

简短的答案是-您所要求的是什么，但正如明确指出的那样，尚不支持(尽管强调不够，但没人喜欢强调这些限制))在当前

很多关系需要双方的集合导航属性.

也在原始跟踪项的末尾多对多(跳过)导航属性#19003 您可以看到基本相同的问题

您好，有没有一种方法可以避免为其中一个实体定义属性?例如

  builder.HasMany(p => p.Tags).WithMany();//注意`WithMany`中没有参数 

团队的回应是

尚未#3864

直接指向通过阴影导航#3864支持单向多对多关系，这是相应的当前未解决问题，似乎已计划在6.0版本中发布.

确切地说，只有团队成员才能回答这个问题，但这很可能是由于通常缺乏足够的时间来在特定的时间内交付特定的版本.用于实现实际功能的全新(并非完全完整)概念(跳过导航)，并进行了许多可能的改进，例如支持非多对多跳过导航#21673 ，有问题的导航以及许多其他导航-您可以在此处

因此，您至少需要一个私有的 ICollection< User>用户属性或字段，不进行序列化并且配置良好

  modelBuilder.Entity< User>().HasMany(e => e.Roles).WithMany("Users"); 

并接受将由EF Core 导航修正填充的事实.或者更好的方法是，与公共导航属性一起使用，然后等待该功能的正式实施.

I've configured my DbContext (EF Core 5.0) with the following code:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<User>()
        .HasMany(p => p.Roles)
        .WithMany(p => p.Users)
        .UsingEntity<Dictionary<string, object>>("UsersToRoles",
            x => x.HasOne<Role>().WithMany().HasForeignKey("UserId"),
            x => x.HasOne<User>().WithMany().HasForeignKey("UserId"),
            x => x.ToTable("UsersToRoles"));

    modelBuilder.Entity<Role>()
        .ToTable("Roles")
        .Property(r => r.Application)
        .IsRequired();

    base.OnModelCreating(modelBuilder);
}

The thing is that I wouldn't like the Role entity to hold a collection of Users. I'm keeping it because EF Core requires it to configure the many-to-many relationship.

Is there a way to create the same relationship, but without having to define the Role.Users navigation property?

解决方案

The short answer is - what are you asking is desired, but not supported yet, as clearly stated (although not enough emphasized, but nobody likes to highlight the limitations) in the beginning of the current Many-to-many section of the official EF Core documentation (emphasis is mine):

Many to many relationships require a collection navigation property on both sides.

Also at the end of the original tracking item Many-to-many (skip) navigation properties #19003 you can see basically the same question

Hello, is there a way to avoid defining the property for one of the entities? e.g.

builder.HasMany(p => p.Tags).WithMany(); // notice no parameter in `WithMany`

and the response from the team is

Not yet #3864

pointing straight to Support unidirectional many-to-many relationships through shadow navigations #3864, which is the corresponding current open issue, and seems like is scheduled for 6.0 release.

As of why exactly, only the team members can answer that, but most likely it's because of the usual lack of enough time to fit something in the limited timeframe for delivering a specific release. A brand new (and not fully complete) concept (skip navigations) used to implement the actual feature, with a lot of possible improvements like Support non-many-to-many skip navigations #21673, the one in question and many others - you can see the current list here Improve many-to-many, skip navigations, and indexer properties #22960. Plus technical difficulties, the lack of shadow navigation property support (although that doesn't stop the other types of relationships which can be configured even w/o a navigation at neither side (how that would be useful is another story)) etc.

A final note in case you are looking for workaround/a way to overcome the current limitation. I usually like to go beyond the EF Core limitations, but here first I don't see a value (I personally look at navigation properties more like metadata representing a relationship in the LINQ queries rather than a storage), and also attempts to overcome it with using directly internal metadata APIs, along with the ugly looking code just led to a different runtime exceptions, which to me proves that the current code really relies on having the "inverse" navigation, and that is constrained in many places.

So at minimum you need a private ICollection<User> Users property or field, excluded from serialization and fluently configured

modelBuilder.Entity<User>().HasMany(e => e.Roles).WithMany("Users");

and live with the fact that it will be populated from the EF Core navigation fixup. Or better off, just live with the public navigation property and wait for the official implementation of the feature.

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