如何首先在EF代码中创建持久化的计算列？ [英] How to make persisted computed column in EF code first?

问题描述

如何使此列与数据库中的 PERSISTED COMPUTED列相似？

How do I get this column as similar to a PERSISTED COMPUTED column in the database?

我当前的尝试（它将所有CompCol行加载为null种子）：

    public class Call
    {
        public Call()
        {
        }

        [Key]
        public int Id { get; set; }

        [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
        public string CompCol
        {
            get
            {
                return "ABC-" + Convert.ToString(Id).PadLeft(5, '0');
            }
            protected set {}
        }
}

推荐答案

我找到的解决方案是：

1. 确保已启用自动迁移关。这样一来，VS便可以生成脚本（流利的api代码）供我们进一步自定义，而不仅仅是运行它。因此，在配置类中：

1. Make sure auto migrations are turned off. This is so that VS will generate a script (fluent api code) for us to further customise instead of just running it. So in the configuration class :

public Configuration()
{
    AutomaticMigrationsEnabled = false;
}

将字段添加到类中并按如下方式进行设置，则setter是私有的，因为我们显然无法写入计算字段：

Add the field to the class and set it as computed like so, the setter is private because we obviously cannot write to a computed field :

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

然后执行 add-migration [xyz-name] 在Package Manager控制台中生成迁移代码，该代码将以给定名称显示在migrations文件夹下。

Then do an add-migration [xyz-name] in the Package Manager Console to generate the migration code, which will appear under the migrations folder with the given name.

迁移注释掉 Up（）中的代码，并添加自定义SQL，如下所示：

Inside the migration comment out the code in Up() and add custom SQL like so :

public override void Up()
{
    //AddColumn("dbo.Calls", "BreakdownNo", c => c.String());
    Sql("ALTER TABLE dbo.Calls ADD BreakdownNo AS ('BD'+RIGHT('00000'+ CAST(Id AS VARCHAR), 6))");
}

执行更新数据库在PM中，它应该正确添加计算列。

Do an update-database in the PM and it should add the computed column properly.

更多说明：如果公式错误，则必须通过执行 update-database -targetMigration：[迁移名称返回] 来还原迁移。然后再使用另一个 add-migration名称并在此处修改公式，最后以update-database结束。也许有更好的方法，但这是我发现和使用的方法。

FURTHER NOTES : If you get the formula wrong then you will have to revert back the migration by doing an update-database -targetMigration: [name of migration to go back to] then do another add-migration name and amend your formula there, finishing off with update-database. There may be a better way but this is what I found and used.

但是我还没有找到使该字段持久化的方法。

I did not however find a way to make the field persisted yet.

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