在使用依赖注入的过程当中，除了应用设计模式注意代码的变化隔离之外，另外一个重要的内容就是生命周期控制。
每次获取都是新的实例
前文中用到的方式都是这样的效果。在容器中每次获取同一个接口的实现，每次获取到的都是不同的实例。读者可以翻阅一下先前的示例代码回顾一下。
单例模式
单例模式也是一种常见的设计模式，这种设计模式。主要是为了解决某些特定需求时不希望特定的实例过多，而采用单个实例的设计模式。
在C#之中，最为容易理解的一种单例模式的应用便是静态成员，这点显而易见，以下获取系统时间的代码。便是一种单例模式。
using System;
using System.Threading;
namespace Use_Dependency_Injection_With_Lifetime_Scope_Control
{
public static class Demo1
{
public static void Run()
{
Console.WriteLine($"第一次获取时间：{DateTime.Now}");
Thread.Sleep(1000);
Console.WriteLine($"第二次获取时间：{DateTime.Now}");
Thread.Sleep(1000);
Console.WriteLine($"第三次获取时间：{DateTime.Now}");
}
}
}
|
每隔一秒钟获取一次系统时间。DateTime.Now是DateTime类型提供的静态属性。在C#语言之中这可以被看做一种单例模式。
但是，存在一个问题，那就是单元测试的可行性。简单来说，这段代码的运行结果会随着时间的变化而变化，每次运行的结果都不相同，这样通常来说是不可测的。因此，应用依赖注入进行一下改造。
using Autofac;
using System;
using System.Threading;
namespace Use_Dependency_Injection_With_Lifetime_Scope_Control
{
public static class Demo2
{
public static void Run()
{
var cb = new ContainerBuilder();
cb.RegisterType<StaticClockByOneTime>()
.As<IClock>()
.SingleInstance();
var container = cb.Build();
var clock = container.Resolve<IClock>();
Console.WriteLine($"第一次获取时间：{clock.Now}");
Thread.Sleep(1000);
clock = container.Resolve<IClock>();
Console.WriteLine($"第二次获取时间：{clock.Now}");
Thread.Sleep(1000);
clock = container.Resolve<IClock>();
Console.WriteLine($"第三次获取时间：{clock.Now}");
}
public interface IClock
{
DateTime Now { get; }
}
public class StaticClockByOneTime : IClock
{
private DateTime _firstTime = DateTime.MinValue;
public DateTime Now
{
get
{
if (_firstTime == DateTime.MinValue)
{
_firstTime = DateTime.Now;
}
return _firstTime;
}
}
}
}
}
|
简要分析。通过改造之后引入了新的接口获取当前系统时间。由于接口的存在，我们可以替换接口的实现。
此处使用了一个有趣的实现StaticClockByOneTime。简单来说，这个实例如果获取过一次时间之后，时间就不会变化。
为这个特性作支撑的，便是SingleInstance这个方法。此方法将StaticClockByOneTime注册时标记为了“单例”。因此，从容器中获取IClock实例时始终得到的是同一个实例。就这样，便即实现了单例，又实现了可以自主控制时间的需求。
读者可以将上文代码中的SingleInstance代码去掉来体验单例和非单例运行结果的区别。
生命周期内单例
上文的单例是一种全局性的单例配置。只要容器建立起来，在容器内就是完全单例的。但在实际的应用场景中可能需要在某个特定生命周期内的单例，也可以成为局部单例。
业务需求
以下实例代码都将完成如下定义的一个业务场景：从A账号转账给B账号，转账数额为C，则A账号减少数额C，B账号增加数额C。
有关联的输出日志
转账影响了两个账号余额，现在考虑输出两条余额更新的日志，并且在日志中需要包含相同的转账流水号。
using Autofac;
using System;
using System.Collections.Generic;
namespace Use_Dependency_Injection_With_Lifetime_Scope_Control
{
public static class Demo3
{
public static void Run()
{
var cb = new ContainerBuilder();
cb.RegisterType<AccountBll>().As<IAccountBll>();
cb.RegisterType<AccountDal>().As<IAccountDal>();
cb.RegisterType<ConsoleLogger>().As<ILogger>()
.InstancePerLifetimeScope();
var container = cb.Build();
using (var beginLifetimeScope = container.BeginLifetimeScope())
{
var accountBll = beginLifetimeScope.Resolve<IAccountBll>();
accountBll.Transfer("yueluo", "newbe", 333);
accountBll.Transfer("yueluo", "newbe", 333);
}
}
public interface ILogger
{
void BeginScope(string scopeTag);
void Log(string message);
}
public class ConsoleLogger : ILogger
{
private string _currenctScopeTag;
public void BeginScope(string scopeTag)
{
_currenctScopeTag = scopeTag;
}
public void Log(string message)
{
Console.WriteLine(string.IsNullOrEmpty(_currenctScopeTag)
? $"输出日志：{message}"
: $"输出日志：{message}[scope:{_currenctScopeTag}]");
}
}
public interface IAccountBll
{
void Transfer(string fromAccountId, string toAccountId, decimal amount);
}
public class AccountBll : IAccountBll
{
private readonly ILogger _logger;
private readonly IAccountDal _accountDal;
public AccountBll(
ILogger logger,
IAccountDal accountDal)
{
_logger = logger;
_accountDal = accountDal;
}
public void Transfer(string fromAccountId, string toAccountId, decimal amount)
{
_logger.BeginScope(Guid.NewGuid().ToString());
var fromAmount = _accountDal.GetBalance(fromAccountId);
var toAmount = _accountDal.GetBalance(toAccountId);
fromAmount -= amount;
toAmount += amount;
_accountDal.UpdateBalance(fromAccountId, fromAmount);
_accountDal.UpdateBalance(toAccountId, toAmount);
}
}
public interface IAccountDal
{
decimal GetBalance(string id);
void UpdateBalance(string id, decimal balance);
}
public class AccountDal : IAccountDal
{
private readonly ILogger _logger;
public AccountDal(
ILogger logger)
{
_logger = logger;
}
private readonly Dictionary<string, decimal> _accounts = new Dictionary<string, decimal>
{
{"newbe",1000},
{"yueluo",666},
};
public decimal GetBalance(string id)
{
return _accounts.TryGetValue(id, out var balance) ? balance : 0;
}
public void UpdateBalance(string id, decimal balance)
{
_logger.Log($"更新了 {id} 的余额为 {balance}");
_accounts[id] = balance;
}
}
}
}
|
简要分析。以上代码的关键点：
- 在注册
ILogger时，注册为了生命周期内单例。 - 在获取
IAccountBll时，开启了一个生命周期，那么在这个生命周期内获取的ILogger实例都是同一个。 - 在
IAccountBll内使用ILogger记录了转账流水号。
读者可以尝试将InstancePerLifetimeScope去除，观察运行效果的不同。
使用相同的数据库事务
转账从现有的代码结构而言，需要开启数据库事务才能够确保在数据入库时是无误的。从三层结构的角度来说，通常需要调用多个具有修改数据库数据功能的DAL方法时，将会开启事务从而确保这些DAL方法的执行是正确的。
为了实现这个特性，首先准备一些基础的类。
using System;
using System.Data;
namespace Use_Dependency_Injection_With_Lifetime_Scope_Control
{
public interface IExecuteSqlDbConnection : IDbConnection
{
void ExecuteSql(string sql, object[] ps, IDbTransaction dbTransaction = null);
}
public class ConsoleDbConnection : IExecuteSqlDbConnection
{
public delegate ConsoleDbConnection Factory();
public void Dispose()
{
Console.WriteLine("数据库连接：释放");
}
public IDbTransaction BeginTransaction()
{
return new ConsoleOutDbTransaction(this, IsolationLevel.Unspecified);
}
public IDbTransaction BeginTransaction(IsolationLevel il)
{
return new ConsoleOutDbTransaction(this, il);
}
public void Close()
{
Console.WriteLine("数据库连接：关闭");
}
public void ChangeDatabase(string databaseName)
{
throw new NotSupportedException();
}
public IDbCommand CreateCommand()
{
throw new NotSupportedException();
}
public void Open()
{
throw new NotSupportedException();
}
public string ConnectionString { get; set; }
public int ConnectionTimeout
{
get { throw new NotSupportedException(); }
}
public string Database
{
get { throw new NotSupportedException(); }
}
public ConnectionState State
{
get { throw new NotSupportedException(); }
}
public void ExecuteSql(string sql, object[] ps, IDbTransaction dbTransaction = null)
{
if (dbTransaction == null)
{
Console.WriteLine($"无事务执行：{string.Format(sql, ps)}");
}
else
{
Console.WriteLine($"有事务执行：{string.Format(sql, ps)}");
}
}
}
public class ConsoleOutDbTransaction : IDbTransaction
{
public ConsoleOutDbTransaction(IDbConnection connection, IsolationLevel isolationLevel)
{
Connection = connection;
IsolationLevel = isolationLevel;
}
public void Dispose()
{
Console.WriteLine("事务：释放");
}
public void Commit()
{
Console.WriteLine("事务：提交");
}
public void Rollback()
{
Console.WriteLine("事务：回滚");
}
public IDbConnection Connection { get; }
public IsolationLevel IsolationLevel { get; }
}
}
|
具备了数据库链接和事务的基础类后，假设我们不采用生命周期控制的方案。那么一种实现方案如下
using Autofac;
using System;
using System.Collections.Generic;
using System.Data;
namespace Use_Dependency_Injection_With_Lifetime_Scope_Control
{
public static class Demo4
{
public static void Run()
{
var cb = new ContainerBuilder();
cb.RegisterType<AccountBll>().As<IAccountBll>();
cb.RegisterType<AccountDal>().As<IAccountDal>();
cb.RegisterType<DbFactory>().As<IDbFactory>();
cb.RegisterType<ConsoleDbConnection>().AsSelf();
var container = cb.Build();
using (var beginLifetimeScope = container.BeginLifetimeScope())
{
var accountBll = beginLifetimeScope.Resolve<IAccountBll>();
accountBll.Transfer("yueluo", "newbe", 333);
}
}
public interface IDbFactory
{
IExecuteSqlDbConnection CreateDbConnection();
}
public class DbFactory : IDbFactory
{
private readonly ConsoleDbConnection.Factory _factory;
public DbFactory(
ConsoleDbConnection.Factory factory)
{
this._factory = factory;
}
public IExecuteSqlDbConnection CreateDbConnection()
{
return _factory();
}
}
public interface IAccountBll
{
void Transfer(string fromAccountId, string toAccountId, decimal amount);
}
public class AccountBll : IAccountBll
{
private readonly IDbFactory _dbFactory;
private readonly IAccountDal _accountDal;
public AccountBll(
IDbFactory dbFactory,
IAccountDal accountDal)
{
_dbFactory = dbFactory;
_accountDal = accountDal;
}
public void Transfer(string fromAccountId, string toAccountId, decimal amount)
{
using (var dbConnection = _dbFactory.CreateDbConnection())
{
using (var transaction = dbConnection.BeginTransaction())
{
try
{
var fromAmount = _accountDal.GetBalance(fromAccountId);
var toAmount = _accountDal.GetBalance(toAccountId);
fromAmount -= amount;
toAmount += amount;
_accountDal.UpdateBalance(fromAccountId, fromAmount, dbConnection, transaction);
_accountDal.UpdateBalance(toAccountId, toAmount, dbConnection, transaction);
transaction.Commit();
}
catch (Exception)
{
transaction.Rollback();
throw;
}
}
}
}
}
public interface IAccountDal
{
decimal GetBalance(string id);
void UpdateBalance(string id, decimal balance, IExecuteSqlDbConnection dbConnection = null, IDbTransaction dbTransaction = null);
}
public class AccountDal : IAccountDal
{
private readonly IDbFactory _dbFactory;
public AccountDal(
IDbFactory dbFactory)
{
_dbFactory = dbFactory;
}
private readonly Dictionary<string, decimal> _accounts = new Dictionary<string, decimal>
{
{"newbe",1000},
{"yueluo",666},
};
public decimal GetBalance(string id)
{
return _accounts.TryGetValue(id, out var balance) ? balance : 0;
}
public void UpdateBalance(string id, decimal balance, IExecuteSqlDbConnection dbConnection = null, IDbTransaction dbTransaction = null)
{
if (dbConnection == null)
{
dbConnection = _dbFactory.CreateDbConnection();
dbConnection.ExecuteSql("更新语句：更新 {0} 余额为 {1}", new object[] { id, balance });
_accounts[id] = balance;
}
else
{
dbConnection.ExecuteSql("更新语句：更新 {0} 余额为 {1}", new object[] { id, balance }, dbTransaction);
_accounts[id] = balance;
}
}
}
}
}
|
简要分析，上例代码中关键点：
IAccountDal.UpdateBalance支持传入数据库链接和事务对象，这样在IAccountBll既可以开启事务确保方法在一个事务内执行，也可以不开启事务，进行分事务执行。
这样做的缺点也比较明显。DAL层实现比较麻烦。
假如参照上文中“日志”的处理方案，将数据库链接和事务作为生命周期内单例来控制，实现起来将更加方便。
using Autofac;
using System;
using System.Collections.Generic;
using System.Data;
namespace Use_Dependency_Injection_With_Lifetime_Scope_Control
{
public static class Demo5
{
public static void Run()
{
var cb = new ContainerBuilder();
cb.RegisterType<AccountBll>().As<IAccountBll>();
cb.RegisterType<AccountDal>().As<IAccountDal>();
cb.RegisterType<DbFactory>().As<IDbFactory>()
.InstancePerLifetimeScope();
cb.RegisterType<ConsoleDbConnection>().AsSelf();
var container = cb.Build();
using (var beginLifetimeScope = container.BeginLifetimeScope())
{
var accountBll = beginLifetimeScope.Resolve<IAccountBll>();
accountBll.Transfer("yueluo", "newbe", 333);
}
}
public interface IDbFactory
{
IExecuteSqlDbConnection CreateDbConnection();
}
public class DbFactory : IDbFactory
{
private readonly ConsoleDbConnection.Factory _factory;
public DbFactory(
ConsoleDbConnection.Factory factory)
{
this._factory = factory;
}
private IExecuteSqlDbConnection _connection;
public IExecuteSqlDbConnection CreateDbConnection()
{
return _connection ?? (_connection = new TransactionOnceDbConnection(_factory()));
}
}
public class TransactionOnceDbConnection : IExecuteSqlDbConnection
{
private readonly IExecuteSqlDbConnection _innerConnection;
private IDbTransaction _innerDbTransaction;
public TransactionOnceDbConnection(
IExecuteSqlDbConnection innerConnection)
{
_innerConnection = innerConnection;
}
public void Dispose()
{
_innerConnection.Dispose();
}
public IDbTransaction BeginTransaction()
{
if (_innerDbTransaction != null)
{
return _innerDbTransaction;
}
return _innerDbTransaction = _innerConnection.BeginTransaction();
}
public IDbTransaction BeginTransaction(IsolationLevel il)
{
if (_innerDbTransaction != null)
{
return _innerDbTransaction;
}
return _innerDbTransaction = _innerConnection.BeginTransaction(il);
}
public void Close()
{
_innerConnection.Close();
}
public void ChangeDatabase(string databaseName)
{
_innerConnection.ChangeDatabase(databaseName);
}
public IDbCommand CreateCommand()
{
return _innerConnection.CreateCommand();
}
public void Open()
{
_innerConnection.Open();
}
public string ConnectionString
{
get => _innerConnection.ConnectionString;
set => _innerConnection.ConnectionString = value;
}
public int ConnectionTimeout => _innerConnection.ConnectionTimeout;
public string Database => _innerConnection.Database;
public ConnectionState State => _innerConnection.State;
public void ExecuteSql(string sql, object[] ps, IDbTransaction dbTransaction = null)
{
_innerConnection.ExecuteSql(sql, ps, _innerDbTransaction ?? dbTransaction);
}
}
public interface IAccountBll
{
void Transfer(string fromAccountId, string toAccountId, decimal amount);
}
public class AccountBll : IAccountBll
{
private readonly IDbFactory _dbFactory;
private readonly IAccountDal _accountDal;
public AccountBll(
IDbFactory dbFactory,
IAccountDal accountDal)
{
_dbFactory = dbFactory;
_accountDal = accountDal;
}
public void Transfer(string fromAccountId, string toAccountId, decimal amount)
{
using (var dbConnection = _dbFactory.CreateDbConnection())
{
using (var transaction = dbConnection.BeginTransaction())
{
try
{
var fromAmount = _accountDal.GetBalance(fromAccountId);
var toAmount = _accountDal.GetBalance(toAccountId);
fromAmount -= amount;
toAmount += amount;
_accountDal.UpdateBalance(fromAccountId, fromAmount);
_accountDal.UpdateBalance(toAccountId, toAmount);
transaction.Commit();
}
catch (Exception)
{
transaction.Rollback();
throw;
}
}
}
}
}
public interface IAccountDal
{
decimal GetBalance(string id);
void UpdateBalance(string id, decimal balance);
}
public class AccountDal : IAccountDal
{
private readonly IDbFactory _dbFactory;
public AccountDal(
IDbFactory dbFactory)
{
this._dbFactory = dbFactory;
}
private readonly Dictionary<string, decimal> _accounts = new Dictionary<string, decimal>
{
{"newbe",1000},
{"yueluo",666},
};
public decimal GetBalance(string id)
{
return _accounts.TryGetValue(id, out var balance) ? balance : 0;
}
public void UpdateBalance(string id, decimal balance)
{
var dbConnection = _dbFactory.CreateDbConnection();
dbConnection.ExecuteSql("更新语句：更新 {0} 余额为 {1}", new object[] { id, balance });
_accounts[id] = balance;
}
}
}
}
|
简要分析，上例代码关键点：
- 通过装饰模式实现了
TransactionOnceDbConnection，支持一次开启事务之后，后续操作都使用相同事务。 - 修改了
DbFactory，实现一次开启链接之后，就是用相同链接的特性。 - 将
IDbFactory标记为生命周期内单例。 - 在使用
IAccountBll时，开启了一个生命周期。
这样改造之后，DAL实现时，就不需要关系事务到底是否开启没有，只需要直接执行相关操作即可。
总结
在使用依赖注入的时候，生命周期控制是一个相当重要的课题。读者需要在实践中注意分析。
以上示例代码都是基于较为简单的业务场景与基础代码实现，实际操作中不一定是如此，读者需要在实践中注意分析。
本文由于采用了Autofac作为主要的依赖注入框架，因此生命周期控制方式也采用了框架相关的函数。实际上，绝大多数框都提供了以上提及的生命周期控制方式。在实践中，读者可以找寻相关框架的文档，了解如何应用框架进行生命周期控制。
关于Autofac更加深入的生命周期控制：参考链接。
至此，该系列文章也已完结，希望读者能够从中获益。
本文示例代码地址
教程链接
