Question

鉴于此：

namespace TheEntities
{
    [DataContract(IsReference=true)]    
    public class Question
    {
        [DataMember] public virtual int QuestionId { get; set; }
        [DataMember] public virtual string Text { get; set; }
        [DataMember] public virtual string Poster { get; set; }

        [DataMember] public virtual IList<QuestionComment> Comments { get; set; }
        [DataMember] public virtual IList<Answer> Answers{ get; set; }



        [DataMember] public virtual byte[] RowVersion { get; set; }
    }

    [DataContract]
    public class QuestionComment
    {
        [DataMember] public virtual Question Question { get; set; }        

        [DataMember] public virtual int QuestionCommentId { get; set; }
        [DataMember] public virtual string Text { get; set; }
        [DataMember] public virtual string Poster { get; set; }
    }


    [DataContract(IsReference = true)]
    public class Answer
    {
        [DataMember] public virtual Question Question { get; set; }

        [DataMember] public virtual int AnswerId { get; set; }
        [DataMember] public virtual string Text { get; set; }
        [DataMember] public virtual string Poster { get; set; }

        [DataMember] public virtual IList<AnswerComment> Comments { get; set; }

    }

    [DataContract]
    public class AnswerComment
    {
        [DataMember] public virtual Answer Answer { get; set; }

        [DataMember] public virtual int AnswerCommentId { get; set; }
        [DataMember] public virtual string Text { get; set; }
        [DataMember] public virtual string Poster { get; set; }
    }

}

实体框架在NHibernate的同时没有为Answer，QuestionComment，AnswerComment生成重复的对象。

public Question OpenQuestion(int id)
{
    var repo = QuestionRepository;

    var query = repo.All.Where(y => y.QuestionId == id);

    if (QuestionRepository.GetType() == typeof(EfRepository<Question>))
    {                
        query = query
                .Include("Answers")
                    .Include("Answers.Comments")
                .Include("Comments");

        return query.Single();
    }
    else if (QuestionRepository.GetType() == typeof(NhRepository<Question>))
    {                
        // kinda sad, produces duplicate objects
        query = query
                .FetchMany(x => x.Answers)
                    .ThenFetchMany(x => x.Comments)
                .FetchMany(x => x.Comments);
    }
    else
        throw new Exception("Something unsupported");

    return query.Single();
}

这也会产生重复的对象（深度为三级，使用三种关系）：

query = query
    .FetchMany(x => x.Answers)
    .ThenFetchMany(x => x.Comments)

这也会产生重复的对象（仅限两个级别，但使用三个关系）：

query = query
    .FetchMany(x => x.Answers)
    .FetchMany(x => x.Comments);

这不会产生重复的对象，但是热切的加载仅针对两个级别的深度和两个关系，即从问题到答案。对于要回答的评论和要回答的评论，它们是在单独的查询中执行的。

query = query
    .FetchMany(x => x.Answers);

如果NHibernate只能在两个级别FetchMany上完成它的工作，只有两个关系，为什么还要创建ThenFetchMany（在三个级别上使用，但有错误，有重复的对象）？事实上，如果你想在三个关系中使用它，即使FetchMany也是无用的，它也会产生重复的对象。

NHibernate团队是否仍然不愿意删除ThenFetchMany，因为它无法正常工作？

我的映射没有错误，当我删除了抓取策略时，事情正常工作（即不会产生重复的对象）。

Answer 1

获得独特的结果

对于Linq：

.Distinct()

用于QueryOver

.TrasformUsing(Transformers.DistinctRootentity)

for Criteria

.SetResulttransformer(Transformers.DistinctRootentity)

编辑：有效地这是NH的一个缺点，它将发行笛卡尔积，但这可以改进

repo.All.Where(y => y.QuestionId == id)
        .FetchMany(x => x.Answers)
            .ThenFetchMany(x => x.Comments)
        .Future()

query = repo.All.Where(y => y.QuestionId == id)
        .FetchMany(x => x.Comments)

var result = query.AsEnumerable().Single();

请参阅http://ayende.com/blog/4367/eagerly-loading-entity-associations-efficiently-with-nhibernate

它看起来有点奇怪，但应该做

Answer 2

尝试：

    query.QueryOptions.RegisterCustomAction(c => c.SetResultTransformer(new DistinctRootEntityResultTransformer()));

NHibernate FetchMany在两个以上的表上被破坏了吗？

2 个答案: