如何在nHibernate中部分投影具有多个字段的子对象

本文关键字：字段 对象 nHibernate 中部 投影 | 更新日期: 2023-09-27 18:30:13

我有以下nHibernate查询，该查询根据课程id选择课程，然后在初始获取时返回课程对象的选定字段，查询执行时没有问题。

MatchMode option = ... 
CourseItem courseAlias  = null;
TeacherItem teacherAlias = null;
var query = session.QueryOver<CourseItem>()
    .JoinAlias(c => c.Teacher, () => teacherAlias)
    .Where(c => c.CourseID.IsInsensitiveLike(strNumber, option))
    .SelectList(list => list
               .Select(c => c.CourseID).WithAlias(() => courseAlias.CourseID)
               .Select(c => c.IsActive).WithAlias(() => courseAlias.IsActive)
               .Select(c => c.CourseDesc).WithAlias(() => courseAlias.CourseDesc)
               .Select(c => c.Teacher).WithAlias(() => courseAlias.Teacher))
               .TransformUsing(Transformers.AliasToBean<CourseItem>())
.List<CourseItem>();

我想在查询中更进一步，只返回部分教师对象，假设我只想返回ID和Name。因此，我更新了预测列表如下：

var query = session.QueryOver<CourseItem>()
    .JoinAlias(c => c.Teacher, () => teacherAlias)
    .Where(c => c.CourseID.IsInsensitiveLike(strNumber, option))
    .SelectList(list => list
               .Select(c => c.CourseID).WithAlias(() => courseAlias.CourseID)
               .Select(c => c.IsActive).WithAlias(() => courseAlias.IsActive)
               .Select(c => c.CourseDesc).WithAlias(() => courseAlias.CourseDesc)
               .Select(c => c.Teacher.ID).WithAlias(() => courseAlias.Teacher.ID)
               .Select(c => c.Teacher.Name).WithAlias(() => courseAlias.Teacher.Name))
               .TransformUsing(Transformers.AliasToBean<CourseItem>())
.List<CourseItem>();

该查询不起作用，因为nHibernate不知道如何基于Teacher.ID和Teacher.Name重新排序。是否可以不将整个子对象提取回父对象？

我已经尝试了下面的查询，它起作用了——这不是我完全想要的结果

var query = session.QueryOver<CourseItem>(() => courseAlias)
    .JoinAlias(() => courseAlias.Teacher, () => teacherAlias)
    .Where(() => courseAlias.CourseID.IsInsensitiveLike(strNumber, option))
    .SelectList(list => list
               .Select(() => courseAlias.CourseID)
               .Select(() => courseAlias.IsActive)
               .Select(() => courseAlias.CourseDesc)
               .Select(() => teacher.ID)
               .Select(() => teacher.Name))
    .List<object[]>();

我可以查询正确的值，但无法将其正确转换回课程/教师数据类型。

有什么想法吗？

谢谢！

如何在nHibernate中部分投影具有多个字段的子对象

我们确实可以使用自定义转换器。有一个，我正在使用它来进行非常非常深的投影（包括动态对象-5.1.13。组件，动态组件）

  • DeepTransformer<TEntity>

接受它（如果需要调整它），你的最终查询可能是这样的

// just the last lines are different
var query = session.QueryOver<CourseItem>()
    .JoinAlias(c => c.Teacher, () => teacherAlias)
    .Where(c => c.CourseID.IsInsensitiveLike(strNumber, option))
    .SelectList(list => list
           .Select(c => c.CourseID).WithAlias(() => courseAlias.CourseID)
           .Select(c => c.IsActive).WithAlias(() => courseAlias.IsActive)
           .Select(c => c.CourseDesc).WithAlias(() => courseAlias.CourseDesc)
           // the native WitAlias would not work, it uses expression
           // to extract just the last property
           //.Select(c => c.Teacher.ID).WithAlias(() => courseAlias.Teacher.ID)
           //.Select(c => c.Teacher.Name).WithAlias(() => courseAlias.Teacher.Name))
           // so we can use this way to pass the deep alias
          .Select(Projections.Property(() => teacherAlias.ID).As("Teacher.ID"))
          .Select(Projections.Property(() => teacherAlias.Name).As("Teacher.Name"))
           // instead of this
           // .TransformUsing(Transformers.AliasToBean<CourseItem>())
           // use this
           .TransformUsing(new DeepTransformer<CourseItem>())

如果您的别名与属性名称匹配，则转换器将构建对象树。。。

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