如何在Entity Framework Core 2.0中为拥有的实体类型指定默认属性值？

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我有一个简单的POCO类型，例如

I have a simple POCO type, say something like

public class OwnedEntity { public string stringProperty { get; set; } public decimal decimalProperty { get; set; } public bool boolProperty { get; set; } public int intProperty { get; set; } }

以及具有 OwnedEntity 参考

public class SomeEntity { public string Id { get; set; } public OwnedEntity OwnedEntity { get; set; } }

我按照文档使用EF Core的Fluent API：

I set up the relationship like described in the documentation using EF Core's Fluent API:

protected override void OnModelCreating (ModelBuilder builder) { base.OnModelCreating (builder); builder.Entity<SomeEntity> ().OwnsOne (e => e.OwnedEntity); }

关于如何为 OwnedEntity 。我试图像这样初始化属性：

I can't find anything on how to define default-values for all the properties of OwnedEntity. I tried to initialize the properties like this:

public class OwnedEntity { public string stringProperty { get; set; } = "initial" public decimal decimalProperty { get; set; } = -1M; public bool boolProperty { get; set; } = false; public int intProperty { get; set; } = -1; }

但无效。 [DefaultValueAttribute] 也是如此（但这是意料之中的，因为它是明确提及）。

but with no effect. Same goes with the [DefaultValueAttribute] (but that was to expect since it's explicitly mentioned).

有关如何处理常规实体的初始值的一些信息：

There's a bit of information on how to handle initial values for regular entities:

modelBuilder.Entity<SomeOtherEntity>() .Property(e => e.SomeIntProperty) .HasDefaultValue(3);

但是由于我遇到的是拥有实体类型，所以无法通过访问类型实体< T> 。

But since I'm facing an Owned Entity Type, I can't access the type via Entity<T>.

有没有一种方法可以满足我的需求？

Is there a way of doing what I'm looking for?

有些东西值得提到：

• 我有很多特定实体，其中大多数都使用 OwnsOne 关系
• 在基类中声明所有 OwnedEntity -属性不是一种选择，因为并非所有实体都具有这些属性
• 我使用EF Core 2.0.3和ASP.NET Core MVC 2.0.4

• I have a solid amount of specific entities where most of them are using the OwnsOne relation
• Declaring all OwnedEntity-properties in a base class is not an option since not all the entities have those properties
• I`m using EF Core 2.0.3 and ASP.NET Core MVC 2.0.4

最初，我想新创建一个 SomeEntity 实例，以便为所有嵌入式 SomeEntity.OwnedEntity预置属性。 属性。

Originally, I wanted to have newly created SomeEntity instances to come with preset properties for all of the 'embedded' SomeEntity.OwnedEntity properties.

但是看看我的关联控制器是如何工作的，这一切都说得通...我对创建操作有以下方法：

But looking at how my associated controller works, it all makes sense... I have the following methods for the 'Create' operation:

[HttpGet] public IActionResult Create () { return View (nameof (Create)); } [HttpPost] [ValidateAntiForgeryToken] public async Task<IActionResult> Create (SomeEntity model) { context.Add (model); await context.SaveChangesAsync (); // redirect etc. }

这意味着未创建任何对象用于 Create 的 [HttGet] 重载以及链接到属性的所有HTML输入（通过 as-for ）最初是空的。好的。所以我想这样做的正确方法是手动创建 SomeEntity 的新实例，并将其传递给 Create 像这样的视图：

Which means that no object is created for the [HttGet] overload of Create and all the HTML inputs linked to properties (via asp-for) are initially empty. Okay. So I guess the proper way of doing this is to manually create a new instance of SomeEntity and pass it to the Create view like this:

[HttpGet] public IActionResult Create () { return View (nameof (Create), new SomeEntity()); }

那么这是正确的方法还是要记住更多事情？

Is this the right approach then or are there some more things to keep in mind?

推荐答案

假设您了解EF Core是什么默认值适用于此，并且仅查找 Entity< T>（）。Property（...）等价物。

Assuming you understand what EF Core Default Values are for, and just looking for equivalent of Entity<T>().Property(...) equivalent.

始终使用 ReferenceOwnershipBuilder< TEntity，TRelatedEntity> 类方法为每种所有者类型配置拥有的实体。要访问此类，请使用 OwnsOne 方法，或使用重载类型为 Action< ReferenceOwnershipBuilder< TEntity，TRelatedEntity>> 的第二个参数。

The owned entities are always configured for each owner type by using the ReferenceOwnershipBuilder<TEntity,TRelatedEntity> class methods. To access this class you either use the result of OwnsOne method, or use the OwnsOne overload taking second argument of type Action<ReferenceOwnershipBuilder<TEntity,TRelatedEntity>>.

例如，使用第二种方法：

For instance, using the second approach:

builder.Entity<SomeEntity>().OwnsOne(e => e.OwnedEntity, ob => { ob.Property(e => e.stringProperty) .HasDefaultValue("initial"); ob.Property(e => e.decimalProperty) .HasDefaultValue(-1M); // etc. });