c# - 带有 AliasesToBean 转换器的 Nhibernate 二级缓存

Question

我有一个实体:

public class SalesUnit
{
    public virtual long Id { get; set; }
    public virtual string Name { get; set; }

}

和相关的Dto:

public class SalesUnitDto
{
    public long Id { get; set; }
    public string Name { get; set; }

}

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>();

在我插入二级缓存之前，它一直在工作。因此，如果我取消注释 Cacheable() 行，我将得到异常:

消息:值不能为空。参数名称:别名堆栈跟踪:

   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)

那有什么问题呢？它是 NHibernate 的错误吗？我尝试了不同的供应商但无济于事。我还尝试像这样创建 CacheableResultTransformer:

CacheableResultTransformer.Create(Transformers.AliasToBean<SalesUnitDto>(), new[] { "Id", "Name" }, new[] { true, true })

它可以返回和缓存数据，但只能作为元组(对象[])。我没有设法返回 Dto。

这是演示问题的工作示例:github

Answer 1

事实证明这是 (N)Hibernate 的错误/限制。当缓存被激活时，原始的 IResultTransformer 开始接收 null string[] aliases 参数，这对于 AliasToBeanTransformer 实现，因此您得到异常。

作为解决方法，我建议使用以下自定义扩展方法和转换器，它在调用时存储当前别名，并在传递的参数为 null 时将它们传递给底层 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);
        }
    }
}

您的查询将是:

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>();

针对此场景进行了测试和工作。当然，我不能保证它适用于所有 QueryOver 变体。