实体框架的 SQL 列默认值

SQL column default value with Entity Framework(实体框架的 SQL 列默认值)

问题描述

我正在尝试将 Code-First EF6 与默认 SQL 值一起使用.

I am trying to use Code-First EF6 with default SQL values.

例如，我有一个CreatedDate"列/属性不为空，SQL 中的默认值为getdate()"

For example, I have a "CreatedDate" column/property not null with a default in SQL of "getdate()"

如何在我的代码模型中表示这一点?目前我有:

How do I represent this in my code Model? Currently I have:

<DatabaseGenerated(DatabaseGeneratedOption.Computed)>
Public Property CreatedDate As DateTime

这是否可行，或者即使实际列不应为空，我是否需要使用可为空，因此 EF 在尚未设置时不会发送值:

Will this work, or will I need to use a nullable even though the actual column should be not null, so EF doesn't send a value when it hasn't been set:

<DatabaseGenerated(DatabaseGeneratedOption.Computed)>
Public Property CreatedDate As DateTime?

或者有更好的解决方案吗?

Or is there a better solution out there?

我不希望 EF 处理我的默认值 - 我知道这对我可用，但在我目前的情况下是不可能的.

I don't want EF to handle my defaults - I know this is available to me but not possible in my current situation.

推荐答案

目前在 EF6 中没有一个属性来定义用于某个属性默认值的数据库函数.您可以对 Codeplex 进行投票以实现它:

Currently in EF6 there is not an attribute to define database functions used for a certain property default value. You can vote on Codeplex to get it implemented:

https://entityframework.codeplex.com/workitem/44

实现类似功能的公认方法是将 Computed 属性与 Migrations 一起使用，您可以在其中指定默认数据库函数.

The accepted way to implement something like that is to use Computed properties with Migrations where you specify the default database function.

您的类在 C# 中可能如下所示:

Your class could look like this in C#:

public class MyEntity
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }

    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime Created { get; set; }
}

计算的属性不必是可空的.

The computed property doesn't have to be nullable.

然后您必须运行迁移并手动修改它以包含默认 SQL 函数.迁移可能如下所示:

Then you have to run a migration and modify it by hand to include the default SQL function. A migration could look like:

public partial class Initial : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.MyEntities",
            c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    Name = c.String(),
                    Created = c.DateTime(nullable: false, defaultValueSql: "GetDate()"),
                })
            .PrimaryKey(t => t.Id);

    }

    public override void Down()
    {
        DropTable("dbo.MyEntities");
    }
}

您会注意到 defaultValueSql 函数.这是让计算工作的关键

You will notice the defaultValueSql function. That is the key to get the computation working

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