回滚事务
我们没有使用TDD，所以单元测试最麻烦的就是准备测试的基础数据。我们现在是使用内存仓储来做单元测试，要为每个仓储都构造基础数据，非常麻烦。
前几天看xunit的源码，看到AutoRollbackAttribute这个特性，异常的兴奋 ^_^。怎么就忘了用事务的自动回滚呢？
我们看AutorollbackAttribute的具体实现：
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public
class
AutoRollbackAttribute : BeforeAfterTestAttribute
{
IsolationLevel isolationLevel = IsolationLevel.Unspecified;
TransactionScope scope;
TransactionScopeOption scopeOption = TransactionScopeOption.Required;
long
timeoutInMS = -1;
/// <summary>
/// Gets or sets the isolation level of the transaction.
/// Default value is <see cref="IsolationLevel"/>.Unspecified.
/// </summary>
public
IsolationLevel IsolationLevel
{
get
{
return
isolationLevel; }
set
{ isolationLevel = value; }
}
/// <summary>
/// Gets or sets the scope option for the transaction.
/// Default value is <see cref="TransactionScopeOption"/>.Required.
/// </summary>
public
TransactionScopeOption ScopeOption
{
get
{
return
scopeOption; }
set
{ scopeOption = value; }
}
/// <summary>
/// Gets or sets the timeout of the transaction, in milliseconds.
/// By default, the transaction will not timeout.
/// </summary>
public
long
TimeoutInMS
{
get
{
return
timeoutInMS; }
set
{ timeoutInMS = value; }
}
/// <summary>
/// Rolls back the transaction.
/// </summary>
public
override
void
After(MethodInfo methodUnderTest)
{
scope.Dispose();
}
/// <summary>
/// Creates the transaction.
/// </summary>
public
override
void
Before(MethodInfo methodUnderTest)
{
TransactionOptions options =
new
TransactionOptions();
options.IsolationLevel = isolationLevel;
if
(timeoutInMS > 0)
options.Timeout =
new
TimeSpan(timeoutInMS * 10);
scope =
new
TransactionScope(scopeOption, options);
}
}
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这里使用了.Net Framework自带的TransactionScope。TransactionScope在.NET 2.0中就已经有了，可用于分布式事务。用这种方法来做数据的自动回滚也有一些不足：
- 数据库要支持事务。
- 内部数据库操作的逻辑里没有事务的实现。
很庆幸的是我们的项目正好都满足上面的2点，唯一不足的就是mongodb不支持事务。所以就需要混合仓储实现了，事务数据库使用真实的仓储，mongodb使用内存仓储。
项目中是用VS自带的单元测试框架，也不想因为这一个特性而改用xunit，那就只能动手把这个迁移到VS的单元测试框架里了。
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/// <summary>
/// 单元测试基类
/// </summary>
[TestClass]
public
class
BaseUnitTest
{
IsolationLevel _isolationLevel = IsolationLevel.Unspecified;
TransactionScopeOption _scopeOption = TransactionScopeOption.Required;
TransactionScope _transactionScope;
bool
_openAutoRollback =
true
;
/// <summary>
/// 构造函数
/// </summary>
/// <param name="autoRollback">是否开启自动回滚，默认开启</param>
public
BaseUnitTest(
bool
autoRollback =
true
)
{
_openAutoRollback = autoRollback;
}
/// <summary>
/// 自动回滚事务初始化
/// </summary>
[TestInitialize]
public
void
AutoRollbackBefore()
{
if
(_openAutoRollback)
{
var options =
new
TransactionOptions();
options.IsolationLevel = _isolationLevel;
options.Timeout =
new
TimeSpan(0, 1, 0);
_transactionScope =
new
TransactionScope(_scopeOption, options);
}
}
/// <summary>
/// 自动回滚事务回滚并释放对象
/// </summary>
[TestCleanup]
public
void
AutoRollbackAfter()
{
if
(_openAutoRollback)
{
if
(_transactionScope ==
null
)
throw
new
InvalidOperationException(
"未初始化TransactionScope"
);
//回滚事务
_transactionScope.Dispose();
//释放事务对象
_transactionScope =
null
;
//移除所有的缓存
RemoveHttpRuntimeCache();
}
}
/// <summary>
/// 移除所有的HttpRuntime缓存
/// </summary>
[DebuggerStepThrough]
private
void
RemoveHttpRuntimeCache()
{
var cache = HttpRuntime.Cache.GetEnumerator();
var keys =
new
List<
string
>();
while
(cache.MoveNext())
{
keys.Add(cache.Key.ToString());
}
foreach
(var key
in
keys)
{
HttpRuntime.Cache.Remove(key);
}
}
/// <summary>
/// 设置不自动回滚事务
/// </summary>
protected
void
SetAutoRollbackIsUnavailabled()
{
_openAutoRollback =
false
;
}
}
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上面的RemoveHttpRuntimeCache是因为我们在项目中有使用HttpRuntime缓存，关系数据库中的数据回滚后会导致缓存和数据库不一致，所以一但有开启事务的自动回滚，也要相应的清空内存缓存。
方法很简单，跟大家分享一下，和TransactionScope相关的知识，不清楚的同学可以看下MSDN关于“TransactionScope”的文档。
原文地址：http://blog.moozi.net/archives/use-the-transaction-rollback-to-unit-test.html