InvalidOperationException：尚未为此DbContext配置任何数据库提供程序。可以通过覆盖DbContext来配置提供程序

Question

我正在处理没有存储库模式的项目。我试图从控制器中分离我的业务逻辑，有点像设置业务层。我执行以下操作以获取所有用户。

的DbContext

public class DatabaseContext : DbContext
{
    public DatabaseContext() : base() { }
    public DatabaseContext(DbContextOptions options) : base(options) { }
    public DbSet<User> Users { get; set; }
    public DbSet<OvertimeRequest> OvertimeRequests { get; set; }
    public DbSet<HolidayRequest> HolidayRequests { get; set; }
    public DbSet<PaymentRequest> PaymentRequests { get; set; }
}

OvertimeRequestBusiness

public class OvertimeRequestBusiness
{
    public static OvertimeRequestBusiness Instance { get; } = new 
        OvertimeRequestBusiness();

    public OvertimeRequestBusiness() { }

    public async Task<List<User>> GetAllUsersAsync()
    {
        using (var ctx = new DatabaseContext())
        {
            var query = ctx.Users;
            var res = await query.ToListAsync();
            return res;
        }
    }
}

调节器

[Route("users"), HttpGet]
public async Task<List<User>> GetAllUsers()
{
    return await OvertimeRequestBusiness.Instance.GetAllUsersAsync();
}

而我得到的错误是

InvalidOperationException：尚未为此DbContext配置任何数据库提供程序。可以通过覆盖DbContext.OnConfiguring方法或在应用程序服务提供程序上使用AddDbContext来配置提供程序。如果使用AddDbContext，那么还要确保您的DbContext类型在其构造函数中接受DbContextOptions <TContext>对象，并将其传递给DbContext的基础构造函数**

Answer 1

不改变OvertimeRequestBusiness就是在OnCongfiguring类的DbContext方法中设置db连接字符串：

1. 在`appsettings.json中设置连接字符串：

   "ConnectionStrings": {
       "MyConnectionString": "Server=(localdb)\\mssqllocaldb;Database=RazorPagesMovieContext-1234;Trusted_Connection=True;MultipleActiveResultSets=true"
   },

2. 创建Setting.cs：

   public class Setting
   {
       public static string ConnectionString { get; set; }
   }

3. 在qazxsw poi中配置连接字符串： qazxsw poi
4. 修改Startup.cs： Setting.ConnectionString = Configuration.GetSection("ConnectionStrings:MyConnectionString").Value;

但常见的方法是使用DbContext和依赖注入：

DatabaseContext

Answer 2

你的

public class DatabaseContext : DbContext
{

      public DbSet<User> Users { get; set; }
      public DbSet<OvertimeRequest> OvertimeRequests { get; set; }
      public DbSet<HolidayRequest> HolidayRequests { get; set; }
      public DbSet<PaymentRequest> PaymentRequests { get; set; }

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

}

构造函数需要指向连接字符串。

改变它

https://docs.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext

您的连接字符串位于web.config中

DatabaseContext

Answer 3

我删除了DbContext的默认无参数构造函数，然后在OvertimeRequestBusiness中传递了DbContextBuilderOption作为参数。这对我有用。

OvertimeRequestBusiness现在看起来像这样

public class DatabaseContext : DbContext
{
    // Tell DbContext to look for the "MyConnectionString" in .config.
    public DatabaseContext() : base("MyConnectionString") { }

    public DatabaseContext(DbContextOptions options) : base(options) { }

    public DbSet<User> Users { get; set; }
    public DbSet<OvertimeRequest> OvertimeRequests { get; set; }
    public DbSet<HolidayRequest> HolidayRequests { get; set; }
    public DbSet<PaymentRequest> PaymentRequests { get; set; }
}