如何在Fluent API中声明一对多，以便不需要它？ [英] How to declare a one-to-many in Fluent API so that it's not required?

问题描述

  class Donkey 
 {
 public Guid Id {得到;组; } 
} 
 
 class Monkey 
 {
 public Guid Id {get;组; } 
 public Donkey Donkey {get;组; 
} 
  

我可以配置关系如下。

  protected override void OnModelCreating（DbModelBuilder model）
 {
 base.OnModelCreating（model）; 
 model.HasDefaultSchema（dbo）; 
 ... 
 model.Entity< Monkey> 
 .HasRequired（_ => _.Donkey）
 .WithMany（）
 .Map（_ => _.MapKey（DonkeyId））; 
} 
  

我想让它不需要，即这样>驴属性可以是 null ，但如果不是，它指向该表中的一行。

不知道是否可能，因为作为FK依赖其目标是一个PK，这不可能是空的。但是，在C＃中，这将是完美的。我可以有一个没有附件的自由运行的猴子（因为它的驴是 null ），但是我也可以分配一个驴，我想要EF和导航属性为我取得魔法。 p>

可以实现吗？

解决方案

您可以使用 HasOptional：

  model.Entity< Monkey> 
 .HasOptional（_ => _.Donkey）
 .WithMany（）
 .Map（_ => _.MapKey（DonkeyId））; 
  

Suppose we have the two classes below.

class Donkey
{
  public Guid Id { get; set; }
}

class Monkey
{
  public Guid Id { get; set; }
  public Donkey Donkey { get; set; }  
}

I can configure the relation as follows.

protected override void OnModelCreating(DbModelBuilder model)
{
  base.OnModelCreating(model);
  model.HasDefaultSchema("dbo");
  ...
  model.Entity<Monkey>
    .HasRequired(_ => _.Donkey)
    .WithMany()
    .Map(_ => _.MapKey("DonkeyId"));
}

I'd like to make it not-required, i.e. so that Donkey property can be null but if it isn't, it's pointing to a row in that table.

I'm not sure if it's possible because that being a FK relies on its target to be a PK, which can't be null ever. However, in C#, it'd make a perfect sense. I can have a freely running monkey with no attachments (since its donkey is null) but I also can assign a donkey to it and I want EF and navigational properties to do the fetching magic for me.

Is it possible to achieve?

解决方案

You can use HasOptional:

  model.Entity<Monkey>
    .HasOptional(_ => _.Donkey)
    .WithMany()
    .Map(_ => _.MapKey("DonkeyId"));

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