jpa EntityManager复杂查询
概念
EntityManager：EntityManager是JPA中用于增删改查的接口，它的作用相当于一座桥梁，连接内存中的java对象和数据库的数据存储。可以用getCriteriaBuilder()的方式获取CriteriaBuilder对象。CriteriaBuilder接口：用于构造标准查询、复合条件、表达式、排序等。可以通过createQuery的方式获取CriteriaQuery实例。CriteriaQuery接口：代表一个specific的顶层查询对象，它包含着查询的各个部分，比如：select 、from、where、group by、order by。Root接口：代表Criteria查询的根对象，定义了实体类型，能为将来导航获得想要的结果，它与SQL查询中的FROM子句类似
接下来上代码啦！
1. 注入entitymanager
@PersistenceContext
private EntityManager em;2. 建立连接，执行查询操作
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<ADTO> q = cb.createQuery(ADTO.class);
Root<A> root = q.from(A.class);
Join<A, B> b = root.join("b", JoinType.LEFT);
Join<A, C> c = root.join("c", JoinType.LEFT);
Join<A, D> d = root.join("d", JoinType.LEFT);
Join<A, E> e = root.join("e", JoinType.LEFT);
Join<A, F> f = root.join("f", JoinType.LEFT);
q.multiselect(//备注：ADTO要有对应构造函数哦
root.get("id"),
root.get("version"),
root.get("code"),
root.get("name"),
root.get("isAlterable"),
root.get("mustCharge"),
root.get("isConsignment"),
root.get("memo"),
b.get("id"),
b.get("name"),
c.get("id"),
c.get("description"),
d.get("id"),
d.get("name"),
e.get("id"),
e.get("name"),
f.get("id"),
f.get("name"),
root.get("standardPrice"),
root.get("upperPrice"),
root.get("lowerPrice"),
root.get("isActive")
);//还可以进行where.order by等操作哦
List<ADTO> rs = em.createQuery(q).getResultList();到此就完成啦！！！
拓展
where条件
List<Predicate> predicates = new ArrayList<>();
CriteriaBuilder.In<String> in = cb.in(root.get("code").as(String.class));
for (String code: codes) {
in.value(code);
}
predicates.add(in);
if (startDate != null && !"".equals(startDate)) {
predicateList.add(cb.greaterThan(birthdayPath, startDate));
}
Predicate[] pre = new Predicate[predicates.size()];
q.where(predicates.toArray(pre));or 条件拼接
public List<Predicate> getOrSearchPredicates(CriteriaBuilder cb, Root<T> root, String keywords){
List<Predicate> predicates = new ArrayList<>();
Predicate predicate = null;
Predicate predicate1 = null;
try {
UUID uuid = UUID.fromString(keywords);
predicate1 = cb.equal(root.get("id"), uuid);
}catch (Exception e){
log.info(e.getMessage());
}finally {
Predicate predicate2 = cb.like(root.get("code"), "%"+keywords+"%");
Predicate predicate3 = cb.like(root.get("name"), "%"+keywords+"%");
if (predicate1 != null){
predicate = cb.or(predicate1, cb.or(predicate2,predicate3));
} else {
predicate = cb.or(predicate2, predicate3);
}
}
predicates.add(predicate);
return predicates;
}JPA 动态更新
CriteriaBuilder cb=entityManager.getCriteriaBuilder();
CriteriaUpdate<T> op=cb.createCriteriaUpdate(clazz);
Root<T> root=op.from(clazz);
op.set(fieldName, value);
op.where(cb.equal(root.get(keyName), delta.get(keyName)));
entityManager.createQuery(op).executeUpdate();基于EntityManager的使用
1、最基础的查询
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<User> cq = cb.createQuery(User.class);
Root<User> root = cq.from(User.class); //from User
cq.select(root); //select * from User
javax.persistence.criteria.Predicate pre = cb.equal(root.get("id").as(Integer.class),id);//id=1
cq.where(pre);//where id=1
Query query = entityManager.createQuery(cq);//select u from User u where u.id = 1
System.out.println(query.getResultList());
2、spring data jpa的toPredicate方法
public Predicate toPredicate(Root<RoleEntity> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
List<Predicate> list = new ArrayList<Predicate>();
list.add(cb.equal(root.get("dr").as(Integer.class), delete));
if (StringUtils.isNotBlank(searchParam)) {
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<T> findAll(Specification<T> spec) {
return getQuery(spec, (Sort) null).getResultList();
}
protected TypedQuery<T> getQuery(Specification<T> spec, Sort sort) {
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaQuery<T> query = builder.createQuery(getDomainClass());
Root<T> root = applySpecificationToCriteria(spec, query);
query.select(root);
if (sort != null) {
query.orderBy(toOrders(sort, root, builder));
}
return applyRepositoryMethodMetadata(em.createQuery(query));
}
private TypedQuery<T> applyRepositoryMethodMetadata(TypedQuery<T> query) {
if (metadata == null) {
return query;
}
LockModeType type = metadata.getLockModeType();
TypedQuery<T> toReturn = type == null ? query : query.setLockMode(type);
applyQueryHints(toReturn);
return toReturn;
}
以上为个人经验，希望能给大家一个参考，也希望大家多多支持编程网。
