EntityManager的使用-白红宇

v1、最基础的查询

CriteriaBuilder cb = entityManager.getCriteriaBuilder();CriteriaQuery
      
        cq = cb.createQuery(User.class);Root
       
         root = cq.from(User.class); //from Usercq.select(root); //select * from Userjavax.persistence.criteria.Predicate pre = cb.equal(root.get("id").as(Integer.class),id);//id=1cq.where(pre);//where id=1Query query = entityManager.createQuery(cq);//select u from User u where u.id = 1System.out.println(query.getResultList());

v2、spring data jpa 的 toPredicate 方法

public Predicate toPredicate(Root
      
        root, CriteriaQuery
        query, CriteriaBuilder cb) {    List
       
         list = new ArrayList
        
         ();    list.add(cb.equal(root.get("dr").as(Integer.class), delete));    if (StringUtils.isNotBlank(searchParam)) {
    /*searchParam 为传递参数*/        list.add(cb.or(cb.like(root.get("roleName").as(String.class), cb.literal("%" + searchParam + "%")), cb.like(root.get("roleCode").as(String.class), cb.literal("%" + searchParam + "%"))));    }    // 角色id    if (roleId != null && !("".equals(roleId.trim()))) {        list.add(cb.equal(root.get("id").as(String.class), roleId));    }    // 管理员角色标识    if (category != null && category > 0) {        list.add(cb.equal(root.get("category").as(Integer.class), category));    }    //多角色Id    if (roleids != null && roleids.size() > 0) {        list.add(root.get("id").as(String.class).in(roleids));    }    Predicate[] predicates = new Predicate[list.size()];    query.where(list.toArray(predicates));    query.orderBy(cb.asc(root.get("roleType").as(String.class)), cb.asc(root.get("roleProperty").as(String.class)), cb.asc(root.get("roleCode").as(String.class)));    return query.getRestriction();}

　　参考 org.springframework.data.jpa.repository.support.SimpleJpaRepository 的 findAll方法，如下

public List
      
        findAll(Specification
       
         spec) {    return getQuery(spec, (Sort) null).getResultList();}protected TypedQuery
        
          getQuery(Specification
         
           spec, Sort sort) {    CriteriaBuilder builder = em.getCriteriaBuilder();    CriteriaQuery
          
            query = builder.createQuery(getDomainClass());    Root
           
             root = applySpecificationToCriteria(spec, query); query.select(root); if (sort != null) { query.orderBy(toOrders(sort, root, builder)); } return applyRepositoryMethodMetadata(em.createQuery(query));}private TypedQuery
            
              applyRepositoryMethodMetadata(TypedQuery
             
               query) { if (metadata == null) { return query; } LockModeType type = metadata.getLockModeType(); TypedQuery
              
                toReturn = type == null ? query : query.setLockMode(type); applyQueryHints(toReturn); return toReturn;}

本文转自小眼儿博客园博客，原文链接：http://www.cnblogs.com/hujunzheng/p/6656178.html，如需转载请自行联系原作者