实体框架5：使用DatabaseGeneratedOption.Computed选项 [英] Entity Framework 5: Using DatabaseGeneratedOption.Computed option

问题描述

我有一个使用[DatabaseGenerated（DatabaseGeneratedOption.Computed）]属性的EF5代码优先项目。此选项将覆盖我的设置。

请考虑以下SQL表：

 创建表Vehicle（
 VehicleId int identity（1,1）不为null，
名称varchar（100）不为null默认值（'Not Set'）
）
  

我正在使用SQL默认构造来设置[名称]（如果未设置的话）。

在后面的代码中，我定义了一个类似于以下内容的类：

 公共类Vehicle {
 ... 
 
 [DatabaseGenerated（DatabaseGeneratedOption.Computed）] 
公共字符串ShoulderYN {get;组; } 
} 
  

当我在代码中更新实体时，默认值中设置的值会覆盖我的新设置。

在代码中，我有（伪）：

  vehicle.Name ='车辆更新名称'; 
 _dbContext.Update（车辆）; 
 _dbContext.SaveChanges（）; 
  

预期结果是Vehicle.Name ='Update Vehicle of Name'。

实际结果是Vehicle.Name ='Not Set'。

在EF5中是否可以说如果Vehicle.Name为空/空，使用数据库中定义的值吗？否则，如果我在代码中设置了该值，我想使用该值。

谢谢。 p>

史蒂夫

解决方案

显然，没有。并不是很聪明：）

您可能已经读过，Computed选项只是告诉EF不要更新您的列，因为您将自己在DB端计算值。然后，EF只会从您的数据库中返回新计算的值（在您的情况下为未设置）。

您的基本三个选项是-根据EF源代码文档：

• 无-数据库不生成值。


• 身份-插入行时数据库生成一个值。 / li>
  
• 已计算-插入或更新行时，数据库会生成一个值。

https://github.com/aspnet/EntityFramework6/blob/527ae9ed97e67ed src / EntityFramework / DataAnnotations / Schema / DatabaseGeneratedOption.cs

由于您希望自己做更多的自定义逻辑，因此恐怕您必须自己做。我建议您停止依赖数据库默认约束，并以代码优先的方式进行所有操作。这样，您将具有如下代码：

 公共类Vehicle 
 {
 public Vehicle（）
 {
 this.Name =未设置; 
} 
 
 //没有 Generated属性的情况下
 public string Name {get;组; } 
} 
  

这样，当您创建实体时，它会自动以预期的默认值开始。以后可以通过简单地修改Name属性来更改。

希望它会有所帮助！

I have an EF5 code first project that uses the [DatabaseGenerated(DatabaseGeneratedOption.Computed)] attribute. This option is overriding my settings.

Consider this SQL table:

CREATE TABLE Vehicle (
  VehicleId  int identity(1,1) not null,
  Name varchar(100) not null default ('Not Set')
)

I am using the SQL default construct to set the [Name] is case it is not set.

In code behind, I have a class defined similar to:

public class Vehicle {
   ...

    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public string ShoulderYN { get; set; }
}

When I update the entity in code, the value set in the default overrides my new setting.

In code, I have (pseudo):

vehicle.Name = 'Update Name of Vehicle';
_dbContext.Update(vehicle);
_dbContext.SaveChanges();

The expected result is Vehicle.Name = 'Update Name of Vehicle'.

The actual result is Vehicle.Name = 'Not Set'.

Is there a way in EF5 to say "if Vehicle.Name is null/empty, use the value defined in the database? Otherwise, if I set the value in code, I want to use this value."

Thanks.

Steve

解决方案

Apparently, no there isn't. It's not that smart :)

As you may already read, Computed option just tells the EF not to update your column, because you will compute a value on the DB-side yourself. EF will then just return newly computed value from your database (which in your case is "Not Set").

Your basic three options are - as per EF Source code documentation:

• None - The database does not generate values.
• Identity - The database generates a value when a row is inserted.
• Computed - The database generates a value when a row is inserted or updated.

https://github.com/aspnet/EntityFramework6/blob/527ae18fe23f7649712e9461de0c90ed67c3dca9/src/EntityFramework/DataAnnotations/Schema/DatabaseGeneratedOption.cs

Since you expect a little more custom logic to be done, I'm afraid you would have to do it yourself. I would suggest you stop relying on database default constraint and do everything in code first approach. This way you would have a code like that:

public class Vehicle
{
  public Vehicle()
  {
    this.Name = "Not set";
  }
  
  // Without 'Generated' attribute
  public string Name { get; set; }
}

This way, when your Entity is created, it automatically starts with expected default value. And can be later changed by simply modifying the Name property.

Hope it helps!

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