NHibernate - 检索仅适用于孩子的标准的父母/孩子 [英] NHibernate - Retrieve parent / children with criteria applied only to children

问题描述

我有一个带有子实体列表的父实体.当使用 NHibernate 从 SQL 中检索具有子级的给定父级时，如果没有子级或如果有子级的日期与 where 条件匹配，则它可以正常工作.

I have a parent entity with a list of child entities. When using NHibernate to retrieve a given parent with children from SQL, it works fine if there are no children OR if there are children with dates that match the where condition.

如果存在与 where 子句不匹配的子项，则父项为空.我想让父级初始化为空的子级列表.

If there are children that do not match the where clause, the parent is null. I want to have the parent initialized with an empty list of children.

关于如何修改下面的代码来实现这一点有什么想法吗?

Any thoughts on how I can modify the code below to make this happen?

实体:

public class Parent
{
    public int ParentId;
    public IList<Child> Children { get; set; }

    public Parent()
    {
        Children = new List<Child>();
    }
}

public class Child
{
    public int ChildId;
    public DateTime ChildDate;
    public Parent Parent { get; set; }
}

存储库:

IList<Parent> foundParents = new List<Parent>();

var criteria1 = DetachedCriteria.For<Parent>()
    .Add(Restrictions.Eq("ParentId", parentId))
    .CreateCriteria("Children", JoinType.LeftOuterJoin)
        .Add(Restrictions.Or(
            Restrictions.IsNull("ChildDate"), // no children at all
            Restrictions.And(
                Restrictions.Ge("ChildDate", startDate),
                Restrictions.Le("ChildDate", endDate)
            )
        ));

foundParents = Session
    .CreateMultiCriteria()
    .Add<Parent>(criteria1)
    .SetResultTransformer(new DistinctRootEntityResultTransformer())
    .List()[0] as List<Parent>;

如果我为此编写 SQL，我会将日期比较放在左连接中，而不是放在 where 子句中.我不知道如何用 NHibernate 做到这一点.

If I were writing SQL for this, I would put the date comparison in with the left join and not in the where clause. I can't figure out how to do this with NHibernate.

推荐答案

这需要大量研究 - 找到答案的关键是术语过滤器.我通过从 ANSIJoinFragment.cs 中的 AddJoin 开始挖掘 NHibernate 源代码来发现这个术语 - 该代码支持连接的附加条件，所以我认为这是可能的.

This took alot of research - the key to finding an answer is the term filter. I came across the term by digging through the NHibernate source code starting with AddJoin in ANSIJoinFragment.cs - the code supported additional conditions on the join so I figured it was possible.

无论如何，这里是使用过滤器的修改代码(实体类保持不变).

Anyway, here's the revised code that utilizes filter (entity class remains the same).

存储库:

IList<Parent> foundParents = new List<Parent>();

var criteria1 = DetachedCriteria.For<Parent>()
    .Add(Restrictions.Eq("ParentId", parentId))
    .CreateCriteria("Children", JoinType.LeftOuterJoin);

Session.EnableFilter("dateFilter")
    .SetParameter("startDate", startDate)
    .SetParameter("endDate", endDate);

foundParents = Session
    .CreateMultiCriteria()
    .Add<Parent>(criteria1)
    .SetResultTransformer(new DistinctRootEntityResultTransformer())
    .List()[0] as List<Parent>;

我还必须通过添加 filter 和 filter-def 元素来修改我的 Parent 映射.

I also had to modify my mapping for Parent by adding filter and filter-def elements.

<class name="Parent" table="Parents">

  ...
  <bag name="Children" table="Children">
    ...
    <filter name="dateFilter" 
      condition="ChildDate BETWEEN :startDate and :endDate" />
  </bag>
</class>

<filter-def name="dateFilter">
  <filter-param name="startDate" type="System.DateTime" />
  <filter-param name="endDate" type="System.DateTime" />
</filter-def>

另外，对遇到此问题且不使用过滤器的任何人的警告.如果您决定在带有 where 子句的原始查询没有产生记录时返回没有填充子项的父实体，则任何命中子项集的代码都会导致 NHibernate 加载整个表.

Also, one word of warning for anyone that runs into this problem and doesn't use filters. If you decide to return the Parent entity without the populated children when the original query with the where clause yields no records, any code that hits the set of children will cause NHibernate to load the entire table.

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