如何在Spring Data JPA中实现动态查询
Specifications动态查询方法
代码语言：javascript复制T findOne(Specification<T> spec); //查询单个
List<T> findAll(Specification<T> spec); //查询列表
List<T> findAll(Specification<T> spec, Sort sort); //排序查询
Page<T> findAll(Specification<T> spec, Pageable pageable); //分页查询
long count(Specification<T> spec); //统计查询查询条件-Specification
自定义Specification实现类，实现
代码语言：javascript复制Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb);构造查询条件，参数如下
- Root：查询的对象，查询条件/属性都可以从root对象中获取
- CriteriaQuery：上层查询对象，定义查询方式，一般不用
- CriteriaQueryBuilder：查询对象的构造器，封装了较多的查询条件
动态查询实现
1.新建Maven项目，加入Maven依赖 2.新建entity包，增加实体类Customer 3.新建dao包，增加CustomerDao 4.在test包中新建dao包，增加CustomerDao
findOne(Specification spec)
直接在CustomerDaoTest中书写测试方法
代码语言：javascript复制@Test
public void testFindOne(){
// 匿名内部类
Specification<Customer> specification = (Root<Customer> root, CriteriaQuery<?> query, CriteriaBuilder cb) -> {
// 构造查询条件，实现toPredicate方法
//1.获取比较的属性
Path<Object> custName = root.get("custName");
//2.构造查询条件,equal为精准匹配
Predicate thor_odin = cb.equal(custName, "Thor Odin");
return thor_odin;
};
Customer one = customerDao.findOne(specification);
System.out.println(one);
}使用了lambda表达式实现Specification匿名内部类，测试结果如下
多个条件查询，使用and或者or连接多个查询条件
代码语言：javascript复制@Test
public void testFindOneByMultiCondition(){
Specification<Customer> specification = (Root<Customer> root, CriteriaQuery<?> query, CriteriaBuilder cb) -> {
// 构造查询条件，实现toPredicate方法
//1.获取比较的属性
Path<Object> custName = root.get("custName");
Path<Object> custIndustry = root.get("custIndustry");
//2.构造查询条件,equal为精准匹配
Predicate thor_odin = cb.equal(custName,"Thor Odin");
Predicate asgard = cb.equal(custIndustry, "God of Thunder");
// 组合查询条件,以与的形式组合查询条件，也可以使用or
Predicate mutil = cb.and(thor_odin, asgard);
return mutil;
};
Customer one = customerDao.findOne(specification);
System.out.println(one);
}
findAll(Specification spec)实现模糊查询
代码语言：javascript复制/**
* equal方法可以直接使用path属性及属性值的方式得到Predicate对象
* gt,lt,ge,le,like需要使用path属性.as(属性类型.class)及属性vlaue来得到Predicate对象
*/
@Test
public void testFindAllByLike(){
Specification<Customer> specification = (Root<Customer> root, CriteriaQuery<?> query, CriteriaBuilder cb) -> {
// 构造查询条件，实现toPredicate方法
//1.获取比较的属性
Path<Object> custSource = root.get("custSource");
Predicate like = cb.like(custSource.as(String.class), "FB%");
return like;
};
List<Customer> all = customerDao.findAll(specification);
for (Customer customer : all) {
System.out.println(customer);
}
}
List findAll(Specification spec, Sort sort); 排序查询
代码语言：javascript复制 @Test
public void testFindAllByLikeAsc(){
Specification<Customer> specification = (Root<Customer> root, CriteriaQuery<?> query, CriteriaBuilder cb) -> {
// 构造查询条件，实现toPredicate方法
//1.获取比较的属性
Path<Object> custSource = root.get("custSource");
Predicate like = cb.like(custSource.as(String.class), "FB%");
return like;
};
// 排序规则，倒叙排列
Sort sort = new Sort(Sort.Direction.DESC,"custId");
List<Customer> all = customerDao.findAll(specification,sort);
for (Customer customer : all) {
System.out.println(customer);
}
}
}使用Sort构造排序规则，需要两个参数，排序规则和排序字段，输出结果如下
Page findAll(Specification spec, Pageable pageable)分页查询
先通过save()方法往表中添加数据
代码语言：javascript复制@Test
public void testInsert(){
for (int i = 1; i <= 30; i ) {
Customer customer = new Customer();
customer.setCustName("Spider Army No " i);
customer.setCustIndustry("Queen");
customer.setCustLevel("LV 1");
customerDao.save(customer);
}
}新增分页测试代码
代码语言：javascript复制@Test
public void testPaging(){
Specification spec = null;
// 当前查询页数和每页查询数量
Pageable pageable = new PageRequest(0,5);
Page<Customer> all = customerDao.findAll(null,pageable);
//获取总页数
System.out.println(all.getTotalPages());
// 获取数据总量
System.out.println(all.getTotalElements());
// 获取当前页数据集合
List<Customer> content = all.getContent();
// 遍历集合，得到当前页的所有Customer数据
for (Customer customer : content) {
System.out.println(customer);
}
}执行分页查询测试
成功查出首页数据
