不能使用EF核心遷移

Question

我第一次使用EF核心代碼與Autofac DI一個窗口服務，當我運行Add-遷移TestDD1InitialMigration我得到

No parameterless constructor was found on 'ClientsContext'. Either add a parameterless constructor to 'ClientsContext' or add an implementation of 'IDbContextFactory<ClientsContext>' in the same assembly as 'ClientsContext'. 

錯誤我怎樣才能避免這個錯誤？

在此先感謝

Answer 1

你需要一個上下文工廠因此EF核心可以爲遷移創建的DbContext：

public class MyDbContextFactory : IDbContextFactory<MyDbContext> 
{ 
    private IConfigurationRoot _configuration; 

    public MyDbContextFactory() 
    { 
     var builder = new ConfigurationBuilder() 
      .SetBasePath(System.AppContext.BaseDirectory) 
      .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true); 

     _configuration = builder.Build(); 
    } 

    public MyDbContext Create() 
    { 
     var optionsBuilder = new DbContextOptionsBuilder<MyDbContext>(); 
     optionsBuilder.UseSqlServer(_configuration.GetConnectionString("DefaultConnection"), m => { m.EnableRetryOnFailure(); }); 

     return new MyDbContext(optionsBuilder.Options); 
    } 
} 

而一個appsettings.json文件，你把你的連接字符串：

{ 
    "ConnectionStrings": { 
     "DefaultConnection": "<your_connection_string>" 
    } 
}