工具版本
- asp.net 核心 2.2
- 自发法 4.9.2
问题
我正在尝试将记录器实例注入到已配置为由 Autofac 注入依赖项的类中
设置
我有一个查询数据库的类。 该类具有由 Autofac 注入到其中的连接字符串。 以下设置有效。
未注入记录器的类:
public class ItemQueries
: IItemQueries
{
private readonly string _connectionString = default(string);
public ItemQueries(string connectionString)
{
_connectionString = !string.IsNullOrWhiteSpace(connectionString) ? connectionString : throw new ArgumentNullException(nameof(connectionString));
}
public async Task<ItemViewModel> GetItemAsync(int id)
{
using (var connection = new SqlConnection(_connectionString))
{
connection.Open();
var result = await connection.QueryAsync<dynamic>(
@"SELECT *
FROM dbo.items
WHERE Id=@id"
, new { id }
);
if (result.AsList().Count == 0)
{
throw new KeyNotFoundException();
}
return MapItem(result.FirstOrDefault());
}
}
private ItemViewModel MapItem(dynamic result)
{
return new ItemViewModel()
{
Id = result.Id,
Name = result.Name
};
}
}
这是我在Autofac注册类的方式:
public class ItemModule
: Autofac.Module
{
public string QueriesConnectionString { get; }
public ItemModule(string queriesConnectionString)
{
QueriesConnectionString = queriesConnectionString;
}
protected override void Load(ContainerBuilder builder)
{
builder.Register(c => new ItemQueries(QueriesConnectionString)) // <-- this breaks when I make the below changes because it's looking for an instance of ILogger<ItemQueries>
.As<IItemQueries>()
.InstancePerLifetimeScope();
}
}
但是,我想将我的 Logger 实例注入 ItemQueries
类中,所以我将其注入到构造函数中,如下所示:
private readonly ILogger<ItemQueries> _logger;
private readonly string _connectionString = default(string);
public ItemQueries(ILogger<ItemQueries> logger, string connectionString)
{
_logger = logger;
_connectionString = !string.IsNullOrWhiteSpace(connectionString) ? connectionString : throw new ArgumentNullException(nameof(connectionString));
}
但这破坏了我的 Autofac 模块中的注册。 如何告诉 Autofac ItemQueries
类需要注入记录器实例?
我认为 Autofac 能够计算出ItemQueries
类需要注入ILogger<>
实例(你知道,就像变魔术一样!
您可以在 lambda 注册中解决问题。这就是 lambda 中的上下文参数的用途。
builder
.Register(c =>
new ItemQueries(QueriesConnectionString, c.Resolve<ILogger<ItemQueries>>()))
.As<IItemQueries>()
.InstancePerLifetimeScope();
您需要使用Autofac的"工厂"功能。
这是使用工厂的解决方案的设置
private readonly ILogger<ItemQueries> _logger;
private readonly string _connectionString = default(string);
public delegate ItemQueries Factory(string connectionString); // --> here, you create the delegate factory
// connectionString needs to be the first parameter
public ItemQueries(string connectionString, ILogger<ItemQueries> logger)
{
_logger = logger;
_connectionString = !string.IsNullOrWhiteSpace(connectionString) ? connectionString : throw new ArgumentNullException(nameof(connectionString));
}
模块设置应该是这样的:
public class ItemModule: Autofac.Module
{
public string QueriesConnectionString { get; }
public ItemModule(string queriesConnectionString)
{
QueriesConnectionString = queriesConnectionString;
}
protected override void Load(ContainerBuilder builder)
{
builder.RegisterType<ItemQueries>(); // --> not sure if needed
builder.Register(c =>
{
var factory = c.Resolve<ItemQueries.Factory>();
return factory.Invoke(QueriesConnectionString);
})
.As<IItemQueries>()
.InstancePerLifetimeScope();
}
}