EntityFrameworkCore：如何初始化数据库并在用户首次使用应用程序时播种 [英] EntityFrameworkCore: How to initialize a Database and seed it the first time user uses an application

问题描述

我已经使用Microsoft Visual Studio 2015和EntityFrameworkCore构建了一个项目。

I have build a project using Microsoft Visual Studio 2015 and EntityFrameworkCore.

我手动为几个虚拟数据创建了种子，并且正在开发解决方案。现在，我想在服务器中部署，但遇到的问题是，第一次启动应用程序时，由于找不到数据库和数据，它崩溃了。

I have seed manually a couple of dummy data and I was developing my solution. Now, I want to deploy the in the server, but I get the problem that by starting the application the first time, it crash since it does not find a data base and data.

我已经搜索了一下，并使用需要该软件包的 CreateDatabaseIfNotExists 类找到了Visual Studio 2013及更早版本的解决方案： System.Data.Entity
（ http://www.entityframeworktutorial.net/ code-first / database-initialization-strategy-in-code-first.aspx ），但是，此类类和包在EntityFrameworkCore中不存在。

I have googled and I find the solution for Visual Studio 2013 and previous using the CreateDatabaseIfNotExists class that need the package: System.Data.Entity (http://www.entityframeworktutorial.net/code-first/database-initialization-strategy-in-code-first.aspx), however, such classes and packages do not exist in EntityFrameworkCore.

如果用户第一次在EntityFrameworkCore中使用我的应用程序，如何创建并填充至少一行的数据库？

How does I create and populate a database with at least one row if user is using my application by the first time in EntityFrameworkCore?

或等效于实体框架核心中的System.Data.Entity ？

推荐答案

Rowan Miller 说表示 ApplyMigrations 足以创建数据库（如果不存在）并应用所有（必要的）迁移。

Rowan Miller says that ApplyMigrations is enough to create database (if not exist) and apply all (nesessary) migrations.

创建方法如下：

public void CreateDbAndSampleData(IServiceProvider applicationServices)
{
    using (var serviceScope = applicationServices.GetRequiredService<IServiceScopeFactory>().CreateScope())
    {
        using (var db = serviceProvider.GetService<ApplicationDbContext>()) 
        {
            // This will [try to] create database
            // and apply all necessary migrations
            db.Database.AsRelational().ApplyMigrations();

            // then you can check for existing data and modify something
            var admin = db.Users.Where(x => x.Name == "Superadmin").FirstOrDefault();
            if (admin == null)
            {
                db.Users.Add(new User {...});
                db.SaveChanges();
            }
        }
    }
}

从 Startup.cs 调用它，在 Configure 方法的结尾：

And call it from your Startup.cs, at end of Configure method:

CreateDbAndSampleData(app.ApplicationServices);

此代码将在每次应用启动时运行，因此您需要准确且不要覆盖任何非关键数据更改（例如更改用户的评论等）

This code will run on every app startup, so you need to be accurate and do not overwrite any non-critical data changes (like changing Users's comment etc)

您可以使用 MusicStore 应用作为示例： Startup.cs 和 SampleData.cs

You can use MusicStore app as a sample: Startup.cs and SampleData.cs

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