c# - 在 MySql.Data.EntityFrameworkCore 中找不到 Database SetInitializer

Question

我正在使用MySql.Data.EntityFrameworkCore连接mysql的提供者。现在我想在使用 DropCreateDatabaseAlways 初始化数据库时播种数据，但是当我尝试这样使用时却找不到

Database.SetInitializer<SmContext>(new SMDbInitializer<SmContext>());

还有我的SMDbInitializer看起来像这样。

private class SMDbInitializer<T> : DropCreateDatabaseAlways<SmContext> 
{

      protected override void Seed(SmContext context) 
      {

         //Some code
         base.Seed(context);
      }
} 

Answer 1

您可以创建一个 DbInitializer.cs 并调用 dbContext.Database.EnsureDeleted() ;删除现有数据库。

public static class DbInitializer
{
    public static void Initialize(MyDbContext context)
    {
        //Ensures that the database for the context does not exist. If it does not exist, no action is taken. 
        //If it does exist then the database is deleted.
        //Warning: The entire database is deleted an no effort is made to remove just the database objects that are used by the model for this context.
        context.Database.EnsureDeleted();

        //create the database
        context.Database.EnsureCreated();

        // Look for any students.
        if (context.Students.Any())
        {
            return;   // DB has been seeded
        }

        var students = new Student[]
        {
        new Student{FirstMidName="Carson",LastName="Alexander",EnrollmentDate=DateTime.Parse("2005-09-01")},
        new Student{FirstMidName="Meredith",LastName="Alonso",EnrollmentDate=DateTime.Parse("2002-09-01")},
        new Student{FirstMidName="Arturo",LastName="Anand",EnrollmentDate=DateTime.Parse("2003-09-01")},
        new Student{FirstMidName="Gytis",LastName="Barzdukas",EnrollmentDate=DateTime.Parse("2002-09-01")},

        };
        foreach (Student s in students)
        {
            context.Students.Add(s);
        }
        context.SaveChanges();

        //Applies any pending migrations for the context to the database.Will create the database if it does not already exist.
        //Note that this API is mutually exclusive with DbContext.Database.EnsureCreated().
        //EnsureCreated does not use migrations to create the database and therefore the
        //database that is created cannot be later updated using migrations.
        context.Database.Migrate();
    }
}

在 Program.cs 中，修改 Main 方法以在应用程序启动时执行以下操作:

public static void Main(string[] args)
{
  var host = CreateWebHostBuilder(args).Build();

  using (var scope = host.Services.CreateScope())
 {
    var services = scope.ServiceProvider;
    try
    {
        var context = services.GetRequiredService<SchoolContext>();
        DbInitializer.Initialize(context);
    }
    catch (Exception ex)
    {
        var logger = services.GetRequiredService<ILogger<Program>>();
        logger.LogError(ex, "An error occurred while seeding the database.");
    }
}

 host.Run();
}