Question

我有一个实体PrintingFare 和那里的外键 - Printer，那么我如何以这种方式使用Criteria API，以便获得一组打印机，这些打印机具有打印票价？

基本上我有一个带有此字段的课程PrintingFare

@ManyToOne
@JoinColumn(name = "printer_id", foreignKey = @ForeignKey(name = "fk_fares_ref_printer_id"))
private Printer printer;

如何使用Criteria API获取一组打印机？

Answer 1

您应该为查询添加限制

  Criteria criteria = getSession().createCriteria(PrintingFare.class);
  criteria.add(Restrictions.eq("printer.id", printerId));
  List<PrintingFare> list = criteria.list();

  Criteria criteria = getSession().createCriteria(Printer.class);
  criteria.createAlias("printerFairs", "pf").add(Restrictions.in("pf.id", printerFairIds));
  List<Printer> list = criteria.list();

Answer 2

我还没有对此进行测试，但您可以尝试：

Criteria criteria = getSession().createCriteria(PrintingFare.class);
criteria.setProjection(Projections.distinct(Projections.property("printer"));
List<Printer> list = criteria.list();

让我知道它是否有效。它可能需要调整。

Answer 3

如果PrinterFares是从Printer.class端映射的......

Criteria criteria = getSession().createCriteria(Printer.class);
criteria.createAlias("printerFares", "pf");
criteria.add(Restrictions.isNotEmpty("pf"));
crit.setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY);

List<Printer> printers = criteria.list();

如果您无法更改Printer.class的映射...

Criteria criteria = getSession().createCriteria(Printer.class);
// create a subquery
DetachedCriteria dc = DetachedCriteria.forClass(PrinterFare.class);
dc.setProjection(Projections.property("printer.id"));
// restrict by subquery
criteria.add(Subqueries.in("id", dc);
crit.setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY);

List<Printer> printers = criteria.list();

使用Criteria API从表中获取一组连接的实例

3 个答案: