c# - 如何在 nHibernate 中部分投影具有多个字段的子对象

Question

我有以下 nHibernate 查询，它根据类(class) ID 选择一门类(class)，然后在初始提取时返回类(class)对象的选定字段，查询执行时没有任何问题。

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>();

我想更进一步地查询只返回部分教师对象，假设我只想返回 ID 和姓名。因此，我将预计列表更新为如下:

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>();

查询不起作用，因为 nHibernate 不知道如何根据 Teacher.ID 和 Teacher.Name 进行解析。关于是否可以不将整个子对象取回父对象有什么想法吗？

我已经尝试了以下查询并且它有效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类(class)/教师数据类型。

有什么想法吗？

谢谢!

Answer 1

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

• 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，转换器将构建对象树...