AddDbContext是通过配置调用的，但是上下文类型“ MyContext”仅声明无参数的构造函数？ [英] AddDbContext was called with configuration, but the context type 'MyContext' only declares a parameterless constructor?

问题描述

在以下控制台应用程序（.Net core 2.0）中， scaffold-dbcontext 创建了以下 DbContext

In the following console application (.Net core 2.0), the scaffold-dbcontext created the following DbContext

public partial class MyContext : DbContext
{
    public virtual DbSet<Tables> Tables { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        if (!optionsBuilder.IsConfigured) { optionsBuilder.UseSqlServer(Program.Conn); }
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder) { .... }
}

在Main（）中（ static void Main（string [] args）），以下代码

In the Main() (static void Main(string[] args)), the following code

var services = new ServiceCollection();
var conn = configuration.GetConnectionString("MySource");
services.AddDbContext<MyContext>(o => o.UseSqlServer(conn)); // Error

得到以下运行时错误？

got the following run-time error?

AddDbContext是通过配置调用的，但是上下文类型 MyContext仅声明无参数的构造函数。这意味着将永远不会使用传递给AddDbContext的配置

AddDbContext was called with configuration, but the context type 'MyContext' only declares a parameterless constructor. This means that the configuration passed to AddDbContext will never be used

推荐答案

如果通过 AddDbContext 配置 MyContext ，那么您也需要添加一个接收参数为<$ c $类型的构造函数。 c> DbContextOptions< MyContext> 放入您的 MyContext 类中，如下所示

As the error said it if you configure your MyContext through AddDbContext then you need too add a constructor that receive a parameter of type DbContextOptions<MyContext> into your MyContext class like below

public MyContext(DbContextOptions<MyContext> options)
    : base(options)
{ }

如果不这样做，ASP.Net Core将无法注入使用 AddDbContext 设置的配置。

If you don't do that, ASP.Net Core will not be able to inject the configuration you set with AddDbContext.

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