实体框架 - 迁移 - 代码优先 - 每次迁移播种 [英] Entity Framework - Migrations - Code First - Seeding per Migration

问题描述

我正在研究迁移以清理我们的部署过程.将变更推送到生产时所需的人工干预越少越好.

I am looking into Migrations in an effort to clean up our deployment processes. The less manual intervention required when pushing a change to production the better.

我遇到了迁移系统的 3 个主要障碍.如果我想不出一个干净的方法来绕过它们，它们就会被阻止.

I have run into 3 major snags with the migrations system. They are show stoppers if I can not figure out a clean way around them.

1.如何为每次迁移添加种子数据:

我执行命令add-migration"，该命令使用 Up 和 Down 功能构建一个新的迁移文件.现在，我想通过 Up 和 Down 更改自动更改数据.我不想将 Seed 数据添加到 Configuration.Seed 方法中，因为这会针对所有以各种重复问题结束的迁移运行.

I execute the command "add-migration" which scaffolds a new migration file with Up and Down functions. Now, I want to automatically make changes to the data with both Up and Down changes. I don't want to add the Seed data to the Configuration.Seed method as this runs for all migrations which ends in all sorts of duplication problems.

2.如果以上都不可能，我该如何避免重复?

我有一个枚举，我通过它循环将值添加到数据库中.

I have an enum that I loop through to add the values to the database.

foreach(var enumValue in Enum.GetValues(typeof(Access.Level)))
{
    context.Access.AddOrUpdate(
        new Access { AccessId = ((int)enumValue), Name = enumValue.ToString() }
    );
}
context.SaveChanges();

即使我使用 AddOrUpdate，我仍然在数据库中得到重复项.上面的代码让我想到了我的第三个也是最后一个问题:

Even though I am using AddOrUpdate, I still get duplicates in the database. The above code brings me to my 3rd and final problem:

3.我怎样才能播种主键?

我上面代码的枚举是:

public class Access
{
    public enum Level
    {
        None = 10,
        Read = 20,
        ReadWrite = 30
    }
    public int AccessId { get; set; }
    public string Name { get; set; }
}

我指定了我想要作为主键的值，但实体框架似乎忽略了它.他们最终仍然是 1,2,3.我如何使它成为 10、20、30?

I am specifying the values that I want as my primary key, but Entity Framework seems to ignore it. They still end up being 1,2,3. How do I get it to be 10,20,30?

这些 EF 的限制是目前还是有意限制以防止我没有看到的其他类型的灾难?

Are these limitations of EF at the moment or are they intentional constraints to prevent some other kind of catastrophe I am not seeing?

推荐答案

1. 当我有想要通过迁移插入的固定数据时，我使用对 Sql("Insert ...") 的调用将插入内容直接放入 Up() 迁移中.请参阅本页中间的注释:如何插入固定数据
2. 您可以通过调用 AddOrUpdate 重载来防止 Seed 方法中的重复，该重载采用指定自然键的标识符表达式 - 请参阅此答案 和 此博客条目.
3. 默认情况下，整数主键被创建为身份字段.要以其他方式指定，请使用 [DatabaseGenerated(DatabaseGeneratedOption.None)] 属性

1. When I have fixed data that I want to insert with a migration, I put the inserts directly in the Up() migration using calls to Sql("Insert ..."). See the note halfway down this page: how to insert fixed data
2. You prevent duplicates in the Seed method by calling the AddOrUpdate overload that takes an identifier expression specifying the natural key - see this answer and this blog entry.
3. Primary keys that are integers are created as identity fields by default. To specify otherwise use the [DatabaseGenerated(DatabaseGeneratedOption.None)] attribute

我认为这是对 Initializer 和 Seed 方法

以下是如何使用 AddOrUpdate 方法的示例:

Here is an example of how to use the AddOrUpdate method:

foreach(var enumValue in Enum.GetValues(typeof(Access.Level)))
{
    context.Access.AddOrUpdate(
        x => x.Name, //the natural key is "Name"
        new Access { AccessId = ((int)enumValue), Name = enumValue.ToString() }
    );
}

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