[英]Nhibernate 2nd level Cache with AliasesToBean transformer
I have an entity: 我有一个实体:
public class SalesUnit
{
public virtual long Id { get; set; }
public virtual string Name { get; set; }
}
And related Dto: 和相关的Dto:
public class SalesUnitDto
{
public long Id { get; set; }
public string Name { get; set; }
}
I have a very simple query: 我有一个非常简单的查询:
SalesUnitDto result = null;
var list = _session.QueryOver<SalesUnit>()
.SelectList(l => l
.Select(x => x.Id).WithAlias(() => result.Id)
.Select(x => x.Name).WithAlias(() => result.Name))
.TransformUsing(Transformers.AliasToBean<SalesUnitDto>())
//.Cacheable()
.List<SalesUnitDto>();
It was working until I plugged in the second level cache. 在插入第二级缓存之前,它一直有效。 So if I uncomment Cacheable()
line I will get the exception: 因此,如果我取消注释Cacheable()
行,我将得到异常:
Message: Value cannot be null. 消息:值不能为空。 Parameter name: aliases StackTrace: 参数名称:别名StackTrace:
at NHibernate.Transform.AliasedTupleSubsetResultTransformer.IncludeInTransform(String[] aliases, Int32 tupleLength)
at NHibernate.Transform.CacheableResultTransformer.Create(ITupleSubsetResultTransformer transformer, String[] aliases, Boolean[] includeInTuple)
at NHibernate.Loader.Loader.GenerateQueryKey(ISessionImplementor session, QueryParameters queryParameters)
at NHibernate.Loader.Loader.ListUsingQueryCache(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes)
at NHibernate.Impl.SessionImpl.List(CriteriaImpl criteria, IList results)
So what's wrong with that? 那怎么了? Is it a bug of NHibernate? 这是NHibernate的错误吗? I have tried different providers with no avail. 我尝试了其他提供商,但无济于事。 Also I tried to create CacheableResultTransformer like this: 我也试图创建CacheableResultTransformer像这样:
CacheableResultTransformer.Create(Transformers.AliasToBean<SalesUnitDto>(), new[] { "Id", "Name" }, new[] { true, true })
It can return and cache data but only as tuples(object[]). 它可以返回和缓存数据,但只能作为元组(object [])。 I did not manage to return Dto. 我没有设法返回Dto。
Here is the working example to demonstrate a problem: github 这是演示问题的工作示例: github
It turns out to be a bug/limitation of (N)Hibernate. 原来是(N)Hibernate的错误/局限性。 When the caching is activated, the original IResultTransformer
starts receiving null
string[] aliases
argument, which is essential for AliasToBeanTransformer
implementation, hence the exception you are getting. 激活缓存后,原始IResultTransformer
开始接收null
string[] aliases
参数,这对于AliasToBeanTransformer
实现是必不可少的,因此会出现异常。
As a workaround I could suggest the following custom extension method and transformer, which stores the current aliases when called and passes them to the underlying AliasToBeanTransformer
when the passed argument is null
: 作为一种解决方法,我建议使用以下自定义扩展方法和转换器,它们在调用时存储当前别名,并在传递的参数为null
时将其传递给底层的AliasToBeanTransformer
:
public static class NHExtensions
{
public static IQueryOver<TRoot, TSubType> TransformUsingAliasToBean<TRoot, TSubType>(this IQueryOver<TRoot, TSubType> query, Type resultType)
{
ITupleSubsetResultTransformer resultTransformer = new AliasToBeanResultTransformer(resultType);
var criteria = query.UnderlyingCriteria as NHibernate.Impl.CriteriaImpl;
if (criteria != null)
resultTransformer = new CacheableAliasToBeenResultTransformer(resultTransformer, criteria.Projection.Aliases);
return query.TransformUsing(resultTransformer);
}
class CacheableAliasToBeenResultTransformer : ITupleSubsetResultTransformer
{
ITupleSubsetResultTransformer baseTransformer;
string[] aliases;
public CacheableAliasToBeenResultTransformer(ITupleSubsetResultTransformer baseTransformer, string[] aliases)
{
this.baseTransformer = baseTransformer;
this.aliases = aliases;
}
public bool[] IncludeInTransform(string[] aliases, int tupleLength)
{
return baseTransformer.IncludeInTransform(aliases ?? this.aliases, tupleLength);
}
public bool IsTransformedValueATupleElement(string[] aliases, int tupleLength)
{
return baseTransformer.IsTransformedValueATupleElement(aliases ?? this.aliases, tupleLength);
}
public IList TransformList(IList collection)
{
return baseTransformer.TransformList(collection);
}
public object TransformTuple(object[] tuple, string[] aliases)
{
return baseTransformer.TransformTuple(tuple, aliases ?? this.aliases);
}
}
}
and you query would be: 您将查询为:
SalesUnitDto result = null;
var list = _session.QueryOver<SalesUnit>()
.SelectList(l => l
.Select(x => x.Id).WithAlias(() => result.Id)
.Select(x => x.Name).WithAlias(() => result.Name))
.TransformUsingAliasToBean(typeof(SalesUnitDto))
.Cacheable()
.List<SalesUnitDto>();
Tested and working for this scenario. 经过测试并适用于这种情况。 Of course I can't guarantee that it works for all QueryOver
variations. 当然,我不能保证它适用于所有QueryOver
版本。
NHibernate的这个错误已在v4.1.0.4000中修复 !
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