.NET6注入多实现服务报错：部分服务无法构造的原因排查

我正在.NET6中注入实现了IDBActionQuery<T>接口的多个服务，已经在Program.cs中添加了以下代码：

builder.Services.AddTransient<IDBActionQuery<Period>, Select<Period>>();

定义的IDBActionQuery<T>接口如下：

public interface IDBActionQuery<T>
{
    Task<List<T>> execute(string query, params (string name, object val)[] pars);
    Task<List<T>> buildAndExecute();
}

对应的Select<T>实现类：

public class Select<T> : DBMotorBase<T>, IDBActionQuery<T>
{
    private readonly IPrintExceptions exceptions;
    private readonly IGetPropertiesService propertiesService;
    private readonly ISQLParametersService sqlParameterService;
    private readonly ISerializeService serializeService;
    private readonly IDeserealizeService<T> deserealizeService;

    public Select(string _connection,
        IPrintExceptions _exceptions, IGetPropertiesService _propertiesService,
        ISQLParametersService _sqlParameterService, ISerializeService _serializeService,
        IDeserealizeService<T> _deserealizeService) : base(_connection)
    {
        exceptions = _exceptions;
        propertiesService = _propertiesService;
        sqlParameterService = _sqlParameterService;
        serializeService = _serializeService;
        deserealizeService = _deserealizeService;
    }

    private string build(string schema = "dbo")
    {
        ...
    }
    public async Task<List<T>> buildAndExecute()
    {
        return await execute(build(),null);
    }

    public async Task<List<T>> execute(string query, params (string name, object val)[] pars)
    {
        ...
    }

    private async Task<List<T>> processCommand(SqlConnection sql, 
        string query, params (string name, object val)[] pars)
    {
        ...
    }
    private async Task<List<T>> processReader(SqlCommand cmd)
    {
      ....
    }
}

运行时出现错误：Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType:，请问错误原因是什么？

错误原因分析 #

• 无法解析构造函数中的string _connection参数：依赖注入容器默认只能解析已注册的服务类型，字符串属于基础类型，若未手动配置该参数的注入逻辑，容器无法自动提供对应的连接字符串值。
• 未注册构造函数中的其他依赖服务：如果IPrintExceptions、IGetPropertiesService、ISQLParametersService、ISerializeService、IDeserealizeService<T>这些接口的实现类未在Program.cs中注册到DI容器，容器无法构造Select<Period>实例。
• 泛型服务注册不规范：若IDeserealizeService<T>是泛型接口，需以开放泛型方式注册（如AddTransient(typeof(IDeserealizeService<>), typeof(DeserealizeService<>))），仅注册特定泛型参数的版本会导致容器无法匹配对应类型。

解决方向 #

1. 处理_connection字符串参数：

   • 从配置文件读取连接字符串，通过工厂方法手动注入：

     var connectionString = builder.Configuration.GetConnectionString("YourConnectionName");
     builder.Services.AddTransient<IDBActionQuery<Period>>(sp => 
         new Select<Period>(
             connectionString,
             sp.GetRequiredService<IPrintExceptions>(),
             sp.GetRequiredService<IGetPropertiesService>(),
             sp.GetRequiredService<ISQLParametersService>(),
             sp.GetRequiredService<ISerializeService>(),
             sp.GetRequiredService<IDeserealizeService<Period>>()
         )
     );
     

   • 或者将连接字符串注册为单例服务：

     builder.Services.AddSingleton(builder.Configuration.GetConnectionString("YourConnectionName"));
     

2. 注册所有依赖服务：确保构造函数中用到的每个接口都已在DI容器中注册，示例代码：

   builder.Services.AddTransient<IPrintExceptions, PrintExceptions>();
   builder.Services.AddTransient<IGetPropertiesService, GetPropertiesService>();
   builder.Services.AddTransient<ISQLParametersService, SQLParametersService>();
   builder.Services.AddTransient<ISerializeService, SerializeService>();
   builder.Services.AddTransient(typeof(IDeserealizeService<>), typeof(DeserealizeService<>));
   

内容的提问来源于stack exchange，提问作者sofnomic cr