范围实施中的例外

Posted 2023-04-12

【中文标题】范围实施中的例外

【英文标题】：Exception in Scope Implementation

【发布时间】：2022-01-07 03:06:13

【问题描述】：

我正在尝试遵循本教程Repository pattern without ORM，它看起来很有前途，并且做了与教程中完全相同的事情。我的计划很简单，只是从数据库中检索数据：

型号：

public class TeamDetails

    public int TeamId  get; set; 
    public string TeamName  get; set; 


public class DataConnection

    public string DefaultConnection  get; set; 

Ado 存储库：

public abstract class AdoRepository<T> where T : class

    
    private static SqlConnection _connection;
    string connectionString = "Data Source=.;Initial Catalog=DemoApp;Trusted_Connection=True";

    public AdoRepository(string connectionString)
    
        _connection = new SqlConnection(connectionString);
    

    public virtual T PopulateRecord(SqlDataReader reader)
    
        return null;
    
    
    protected List<T> GetRecords(SqlCommand command)
    
        var list = new List<T>();
        command.Connection = _connection;
        _connection.Open();
        try
        
            var reader = command.ExecuteReader();
            try
            
                while (reader.Read())
                    list.Add(PopulateRecord(reader));
            
            finally
            
                // Always call Close when done reading.
                reader.Close();
            
        
        finally
        
            _connection.Close();
        
        return list;
    

    protected T GetRecord(SqlCommand command)
    
        T record = null;
        command.Connection = _connection;
        _connection.Open();
        try
        
            var reader = command.ExecuteReader();
            try
            
                while (reader.Read())
                
                    record = PopulateRecord(reader);
                    break;
                
            
            finally
            
                // Always call Close when done reading.
                reader.Close();
            
        
        finally
        
            _connection.Close();
        
        return record;
    
    
    protected IEnumerable<T> ExecuteStoredProc(SqlCommand command)
    
        var list = new List<T>();
        command.Connection = _connection;
        command.CommandType = CommandType.StoredProcedure;
        _connection.Open();
        try
        
            var reader = command.ExecuteReader();
            try
            
                while (reader.Read())
                
                    var record = PopulateRecord(reader);
                    if (record != null) list.Add(record);
                
            
            finally
            
                // Always call Close when done reading.
                reader.Close();
            
        
        finally
        
            _connection.Close();
        
        return list;
    

界面：

public interface ITeam

    List<TeamDetails> GetAllTeams();

实现团队存储库：

public class TeamRepository : AdoRepository<TeamDetails>, ITeam

    public TeamRepository(string connectionString)
        : base(connectionString)
    
    

    public List<TeamDetails> GetAllTeams()
    
        using (var command = new SqlCommand("select * from Team"))
        
            return GetRecords(command);
        
    

    public override TeamDetails PopulateRecord(SqlDataReader reader)
    
        return new TeamDetails
        
            TeamId = Convert.ToInt32(reader.GetString(0)),
            TeamName = reader.GetString(1)
        ;
    

一个服务接口：

public interface ITeamRepoService

    List<TeamDetails> GetAllTeams();

实施服务：

public class ITeamService : ITeamRepoService

    private readonly ITeam _repository;

    public ITeamService(IOptions<DataConnection> options)
    
        var connection = options.Value;
        _repository = new TeamRepository(connection.DefaultConnection);
    

    public List<TeamDetails> GetAllTeams()
    
        return _repository.GetAllTeams();
    

最后在控制器中调用如下：

 private readonly ITeamService _service;
 private readonly ILogger<WeatherForecastController> _logger;

 public WeatherForecastController(ILogger<WeatherForecastController> logger, ITeamService service)
 
    _logger = logger;
    _service = service;
 

[HttpGet]
public async Task<ActionResult<IEnumerable<TeamDetails>>> Index()

  var teams = _service.GetAllTeams();

  return Ok(teams);

问题是当我运行代码时，它会从 Startup.cs 文件中引发异常：

Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: TodoApi.Interface.ITeam Lifetime: Scoped ImplementationType: TodoApi.Repository.TeamRepository': Unable to resolve service for type 'System.String' while attempting to activate 'TodoApi.Repository.TeamRepository'.)

在启动文件中，我做了以下但没有成功：

services.Configure<DataConnection>(Configuration.GetSection("AppDbConnection"));

services.AddTransient<ITeamRepoService, ITeamService>();
services.AddTransient<ITeam, TeamRepository>();

有什么办法解决吗？

【问题讨论】：

您的 TeamRepository 在构造函数中需要一个字符串，而您还没有告诉 DI 如何构造该对象，因此它试图从 DI 获取一个字符串，这不起作用。向 AddTransient 添加一个构造对象的函数，或者将其更改为使用配置/选项对象而不是字符串。

你能分享一个我可以研究的样本吗？

嗨@user8512043，有什么更新吗？

工作就像一个魅力。非常感谢@Rena。

【参考方案1】：

正如@juunas 所说，您的 TeamRepository 需要一个字符串（connectionString），请在下面更改您的代码：

services.AddTransient<ITeam, TeamRepository>(_ => new TeamRepository("connectionString here"));

参考：

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection?view=aspnetcore-6.0#disposal-of-services