如何在控制器中使用多个 DBContext

Question

如何在控制器中使用多个 DBContext，我尝试以不同的方式重载构造函数？

一些控制器：

public C1(DBContext1 a, DBContext2 b, DBContext3 c)
{ 
}
 //public C1(DBContext1 a)
 //{ 
 //}
 //public C1(DBContext2 b)
 //{
 //}
 //public C1(DBContext3 c)
 //{
 //}

StartUp.cs:

services.AddDbContext<DBContext1>(options =>
options.UseSqlServer(new string(K.ConnectionString))
);

services.AddDbContext<DBContext2>(options =>
options.UseSqlServer(new string(K.ConnectionString))
);

services.AddDbContext<DBContext3>(options =>
options.UseSqlServer(new string(K.ConnectionString))
);

我找到了this，但好像已经过时了

Error(, 前端调用构造函数时):

An unhandled exception has occurred while executing the request.

Exception: System.InvalidOperationException: The DbContextOptions passed to the DBContext1 constructor must be a DbContextOptions. When registering multiple DbContext types make sure that the constructor for each context type has a DbContextOptions parameter rather than a non-generic DbContextOptions parameter. at Microsoft.EntityFrameworkCore.DbContext..ctor(DbContextOptions options) at _4_DWH.DBContext1..ctor(DbContextOptions options) in D:...\DBContext1.cs:line 43 at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor, Boolean wrapExceptions) at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(ServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.b__0(ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType) at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, Boolean isDefaultParameterRequired)
at lambda_method(Closure , IServiceProvider , Object[] ) at Microsoft.AspNetCore.Mvc.Controllers.ControllerActivatorProvider.<>c__DisplayClass4_0.b__0(ControllerContext controllerContext) at Microsoft.AspNetCore.Mvc.Controllers.ControllerFactoryProvider.<>c__DisplayClass5_0.g__CreateController|0(ControllerContext controllerContext) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync() --- End of stack trace from previous location where exception was thrown --- at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync() --- End of stack trace from previous location where exception was thrown --- at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) at Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger) at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.MigrationsEndPointMiddleware.Invoke(HttpContext context) at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware.Invoke(HttpContext httpContext) at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware.Invoke(HttpContext httpContext) at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

数据库上下文：

public class DBContext1 : DbContext
{
    // ...

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(new string(sameConnectionString));
    }

    public DBContext1() : base()
    {

    }

    public DBContext1(DbContextOptions options) : base(options)
    {
    }
}

Answer 1

1. 创建数据库上下文

public class DBContext_A : DbContext
{
    public DBContext_A(DbContextOptions<DBContext_A> options) : base(options)
    {
    }
}

public class DBContext_B : DbContext
{
    public DBContext_B(DbContextOptions<DBContext_B> options) : base(options)
    {
    }
}

public class DBContext_C : DbContext
{
    public DBContext_C(DbContextOptions<DBContext_C> options) : base(options)
    {
    }
}

2. 为每个 DBContext 定义一个连接字符串：

{
  "ConnectionStrings": {
    "Connection_A": "Server=(localdb)\mssqllocaldb;Database=DB_A;Trusted_Connection=True;...",
    "Connection_B": "Server=(localdb)\mssqllocaldb;Database=DB_B;Trusted_Connection=True;...",
    "Connection_C": "Server=(localdb)\mssqllocaldb;Database=DB_C;Trusted_Connection=True;...",
  }
}

3. 启动时注册：

services.AddDbContext<DBContext_A>(ops =>
{
    ops.UseSqlServer(Configuration.GetConnectionString($"Connection_A"));
});

services.AddDbContext<DBContext_B>(ops =>
{
    ops.UseSqlServer(Configuration.GetConnectionString($"Connection_B"));
});

services.AddDbContext<DBContext_C>(ops =>
{
    ops.UseSqlServer(Configuration.GetConnectionString($"Connection_C"));
});

4. 注入控制器：

public FooController : Controller
{
    private readonly DBContext_A _context_A;
    private readonly DBContext_B _context_B;
    private readonly DBContext_C _context_C;

    public FooController(
            DBContext_A context_A, 
            DBContext_B context_B, 
            DBContext_C context_C)
    {
        _context_A = context_A;
        _context_B = context_B;
        _context_C = context_C;
    }
}

Code First 方法的其他最佳实践：

为每个上下文创建一个 class 库，这样当您应用迁移时，每个上下文都会在其自己的项目中有自己的迁移文件夹。

• 解决方案
  • 主项目
    • startup.cs
  • ClassLibrary_A
    • DbContext_A.cs
    • 迁移 // 文件夹
  • ClassLibrary_B
    • DbContext_B.cs
    • 迁移 // 文件夹
  • ClassLibrary_C
    • DbContext_C.cs
    • 迁移 // 文件夹

在多上下文解决方案中应用迁移时；

• 在解决方案资源管理器中，将主项目（startup.cs）设置为“启动项目”
• 将包管理器控制台中的相关 ClassLibrary_A 或 B 或 C 设置为“默认项目”
• 将目标上下文添加到每个 cmd，如下所示：

PM > add-migration Init -Context DBContext_A
PM > update-database -Context DBContext_A

PM > add-migration Init -Context DBContext_B
PM > update-database -Context DBContext_B

PM > add-migration Init -Context DBContext_C
PM > update-database -Context DBContext_C

或者，您可以使用如下完整的 PM 命令：

PM > add-migration Init -Context DBContext_A -Project ClassLibrary_A -StartupProject MainProject
PM > update-database -Context DBContext_A -Project ClassLibrary_A -StartupProject MainProject

PM > add-migration Init -Context DBContext_B -Project ClassLibrary_B -StartupProject MainProject
PM > update-database -Context DBContext_B -Project ClassLibrary_B -StartupProject MainProject

PM > add-migration Init -Context DBContext_C -Project ClassLibrary_C -StartupProject MainProject
PM > update-database -Context DBContext_C -Project ClassLibrary_C -StartupProject MainProject