NetCore 依赖注入之服务之间的依赖关系

简单介绍,直接官方文档

https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/dependency-injection?view=aspnetcore-2.2

public interface IOperation
{
    Guid OperationId { get; }
}

public interface IOperationTransient : IOperation
{
}

public interface IOperationScoped : IOperation
{
}

public interface IOperationSingleton : IOperation
{
}

public interface IOperationSingletonInstance : IOperation
{
}

public class Operation : IOperationTransient, 
    IOperationScoped, 
    IOperationSingleton, 
    IOperationSingletonInstance
{
    public Operation() : this(Guid.NewGuid())
    {
    }

    public Operation(Guid id)
    {
        OperationId = id;
    }

    public Guid OperationId { get; private set; }
}

public class OperationService
{
    public OperationService(
        IOperationTransient transientOperation,
        IOperationScoped scopedOperation,
        IOperationSingleton singletonOperation,
        IOperationSingletonInstance instanceOperation)
    {
        TransientOperation = transientOperation;
        ScopedOperation = scopedOperation;
        SingletonOperation = singletonOperation;
        SingletonInstanceOperation = instanceOperation;
    }

    public IOperationTransient TransientOperation { get; }
    public IOperationScoped ScopedOperation { get; }
    public IOperationSingleton SingletonOperation { get; }
    public IOperationSingletonInstance SingletonInstanceOperation { get; }
}

在 Startup.ConfigureServices 中，根据其指定的生存期，将每个类型添加到容器中：
C#

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

    services.AddScoped<IMyDependency, MyDependency>();
    services.AddTransient<IOperationTransient, Operation>();
    services.AddScoped<IOperationScoped, Operation>();
    services.AddSingleton<IOperationSingleton, Operation>();
    services.AddSingleton<IOperationSingletonInstance>(new Operation(Guid.Empty));

    // OperationService depends on each of the other Operation types.
    services.AddTransient<OperationService, OperationService>();
}

public class IndexModel : PageModel
{
    private readonly IMyDependency _myDependency;

    public IndexModel(
        IMyDependency myDependency, 
        OperationService operationService,
        IOperationTransient transientOperation,
        IOperationScoped scopedOperation,
        IOperationSingleton singletonOperation,
        IOperationSingletonInstance singletonInstanceOperation)
    {
        _myDependency = myDependency;
        OperationService = operationService;
        TransientOperation = transientOperation;
        ScopedOperation = scopedOperation;
        SingletonOperation = singletonOperation;
        SingletonInstanceOperation = singletonInstanceOperation;
    }

    public OperationService OperationService { get; }
    public IOperationTransient TransientOperation { get; }
    public IOperationScoped ScopedOperation { get; }
    public IOperationSingleton SingletonOperation { get; }
    public IOperationSingletonInstance SingletonInstanceOperation { get; }

    public async Task OnGetAsync()
    {
        await _myDependency.WriteMessage(
            "IndexModel.OnGetAsync created this message.");
    }
}

以下两个输出显示了两个请求的结果：

第一个请求：

控制器操作：

暂时性：d233e165-f417-469b-a866-1cf1935d2518
作用域：5d997e2d-55f5-4a64-8388-51c4e3a1ad19
单一实例：01271bc1-9e31-48e7-8f7c-7261b040ded9
实例：00000000-0000-0000-0000-000000000000

OperationService 操作：

暂时性：c6b049eb-1318-4e31-90f1-eb2dd849ff64
作用域：5d997e2d-55f5-4a64-8388-51c4e3a1ad19
单一实例：01271bc1-9e31-48e7-8f7c-7261b040ded9
实例：00000000-0000-0000-0000-000000000000

第二个请求：

控制器操作：

暂时性：b63bd538-0a37-4ff1-90ba-081c5138dda0
作用域：31e820c5-4834-4d22-83fc-a60118acb9f4
单一实例：01271bc1-9e31-48e7-8f7c-7261b040ded9
实例：00000000-0000-0000-0000-000000000000

OperationService 操作：

暂时性：c4cbacb8-36a2-436d-81c8-8c1b78808aaf
作用域：31e820c5-4834-4d22-83fc-a60118acb9f4
单一实例：01271bc1-9e31-48e7-8f7c-7261b040ded9
实例：00000000-0000-0000-0000-000000000000

观察哪个 OperationId 值会在一个请求之内和不同请求之间变化：

• 暂时性 对象始终不同。 第一个和第二个客户端请求的暂时性 OperationId 值对于 OperationService 操作和在客户端请求内都是不同的。 为每个服务请求和客户端请求提供了一个新实例。
• 作用域 对象在一个客户端请求中是相同的，但在多个客户端请求中是不同的。
• 单一实例 对象对每个对象和每个请求都是相同的（不管 Startup.ConfigureServices 中是否提供 Operation 实例）。

接下来是本文重点要说明的

public void ConfigureServices(IServiceCollection services)
{

            services.AddSingleton<SingletonService>();

            services.AddTransient<TransientService>();

            services.AddScoped<ScopedService>();
}

public class SingletonService
    {
        public string Id = Guid.NewGuid().ToString();
        
    }

    public class ScopedService
    {
        public string Id = Guid.NewGuid().ToString();
        
    }

    public class TransientService
    {
        public string Id = Guid.NewGuid().ToString();

        private ScopedService _transient;
        private SingletonService _singleton;

        public TransientService(ScopedService transient, SingletonService singleton)
        {
            _transient = transient;
            _singleton = singleton;
        }


    }

这种情况是可以的,transient 可以依赖 singleton 和 scoped

对于 Transient 服务,它可以被任何服务依赖,但是在依赖的服务中创建的服务的生命周期会跟随依赖的服务
对于 Scoped 服务,它只能被 Transient 和 Scoped 服务依赖,生命周期不会变化,如果要在 Singleton 服务中使用,可以使用 IServiceProvider 的 CreateScope 方法 ,然后 GetService, 但是 生成的 scoped 服务生命周期为 Singleton

对于 Singleton 服务,它可以被任何服务依赖,生命周期不会变化

public class SingletonService
    {
        public string Id = Guid.NewGuid().ToString();
        private ScopedService _scoped;

        public SingletonService(IServiceProvider serviceProvider)
        {
            using (var scope = serviceProvider.CreateScope())
            {
                _scoped = scope.ServiceProvider.GetService<ScopedService>();
            }
        }
    }

    public class ScopedService
    {
        public string Id = Guid.NewGuid().ToString();
        
    }

    public class TransientService
    {
        public string Id = Guid.NewGuid().ToString();


    }

这个 在单例中使用 Scoped 服务