JPA2.0学习笔记---Criteria 查询

来源：互联网发布：四轴飞行器源码编辑：程序博客网时间：2024/06/05 02:50

@Overridepublic List<Book> getBookByTitle(String title) {CriteriaBuilder cb = em.getCriteriaBuilder();CriteriaQuery<Book> c = cb.createQuery(Book.class);Root<Book> book = c.from(Book.class);c.select(book);    //类似于  from Book b  这个里面的bc.distinct(true);  // 去除重复行

//构建参数

List<Predicate> criteList = new ArrayList<Predicate>();if (title != null) {ParameterExpression<String> p = cb.parameter(String.class, "title");//criteList.add(cb.equal(book.get("title"), p));cb.and(cb.equal(book.get("title"), p));}if (criteList.size() == 0) {throw new RuntimeException("no criteria");} else if (criteList.size() == 1) {c.where(criteList.get(0));} else {c.where(cb.and(criteList.toArray(new Predicate[0])));}TypedQuery<Book> q = em.createQuery(c);if(title != null) q.setParameter("title", title);return q.getResultList();}

下面是简化版~ 适合一个

@Overridepublic List<Book> getBookByTitle(String title) {CriteriaBuilder cb = em.getCriteriaBuilder();CriteriaQuery<Book> c = cb.createQuery(Book.class);Root<Book> book = c.from(Book.class);c.select(book);ParameterExpression<String> pe_title = cb.parameter(String.class,"title");c.where(cb.equal(book.get("title"), pe_title));TypedQuery<Book> q = em.createQuery(c);if(title != null) q.setParameter("title", title);return q.getResultList();}