Spring Data -Specification用法和常用查询方法（in，join，equal等）

前言

在这一年里技术更新，从使用Mybatis转为Spring Data,总体感受是终于不用在自己写映射了，也可以少写方法和对应字段了。接下来总结在工作中常用的查询方式和方法，例如equal，join,in等。积少成多，在这里只收藏了用过查询与方法（如果方法可以用得更有，有更多的用法和不足之处请联系我）。

入门例子

controller层，这里是个简单查询获取所有用户并分页

  @GetMapping("/list")
    @ApiOperation(value = "所有用户列表")
    public Result list(@RequestParam Map params) {
        Page page = userService.queryPage(params);
        return Result.ok().put("page", page);
    }

接下对service层的实现,功能是实现关键字搜索，这里因为简单并没有单独将Specification提出来，主要是对Specification接口有个大概的认识。

@Override
    public page queryPage(Map params) {
        //MapUtils方法用来取除params中的方法，来自于 org.apache.commons.collections.MapUtils;
        String keyword = MapUtils.getSrting(params,"keyword");
        Page page = sysUserRepository.findAll(new Specification() {
            @Override
            public Predicate toPredicate(Root root, CriteriaQuery criteriaQuery, CriteriaBuilder criteriaBuilder) {
                List predicates = new ArrayList<>();
                if (StringUtils.isNotBlank(keyword)) {
                    List temp = new ArrayList<>();
                    for (String oneKeyword : keywordCopyStr) {
                        temp.add(criteriaBuilder.like(root.get("mobile"), "%" + oneKeyword + "%"));
                        temp.add(criteriaBuilder.like(root.get("trueName"), "%" + oneKeyword + "%"));
                    }
                    predicates.add(criteriaBuilder.or(temp.toArray(new Predicate[temp.size()])));
                }
                return criteriaQuery.where(predicates.toArray(new Predicate[predicates.size()])).getRestriction();
            }
        });
        return page;
    }

Repository层中为了支持这样的查询，sysUserRepository需要继承JpaRepository（基本查询），JpaSpecificationExecutor（分页），这个接口是不需要再去实现的，到了Repository层就行，再对此进行扩充（比Mybatis简单多了）。

public interface sysUserRepository extends JpaRepository, JpaSpecificationExecutor {

}

Repository层常用写法

1. 按着类字段查询 按着类关系关联查询不需要写语句的查询就不在详细讲解，给个例子看看就行

//查询第一个
EngineerVersionControl findTopByProjectIdAndOldOrderByVersionDesc(String projectId, int old);
//查询存在
boolean existsByProjectId(String projectId);
//排序
List findByProjectIdOrderByVersionDesc(String projectId);
    

2. @Query语句查询

一般不会做物理删除，而是逻辑删除。保存操作使用save或者saveAll方法

//更新 必有@Modifying，和使用hiberna一样，HQL语句的写法
@Transactional(rollbackFor = Exception.class)
@Modifying
@Query("update SysUserEntity  u set u.isDelete = ?2 ,u.gmtModified= ?3  where u.id = ?1 ")
int deleteIsUpdate(String id, int deleted, Date date);

//查询 
@Query("select u from SysUserEntity u where  u.id in ?1 and u.isDelete = 0 ")
Page findAllUser(List userIds, Pageable pageable);

//多表查询
 @Query(value = " select p  from DictionaryEntity p , DictionaryContentEntity w " +
            " Where w.ContentEntity.id = ?1 and p.id = w.DictionaryEntity.id and p.deleted = ?2 ORDER BY p.dictionary")
    List webOnwDictionary(String id,int isDeleted);
    

3.使用@Query实现写sql语句的查询
再spring data 中不仅有HQl语句，在功能太复杂的时候，可以使用sql语句进行本地查询

  @Query(value="select serve.* from service_serve serve " +
            "left join company_info_user cominfo on serve.company_info_user_id=cominfo.company_info_user_id" +
            " left  join user_company company on cominfo.company_info_user_id=company.company_info_user_id " +
            " left  join employee employeeen3_ on company.user_company_id=employeeen3_.user_company_id " +
            " left  join user userentity4_  on employeeen3_.user_id=userentity4_.user_id " +
            " where userentity4_.user_id=?1 and employeeen3_.activity_management_power=1" +
            " order by serve.gmt_create desc " +
            "limit ?2 , ?3 " ,nativeQuery = true)
    List queryByCompany(String userId,int startPoint,int endPoint);

4.@Param（value = “name”）查询，这是两种写法。一种?，一种@Param()

 @Query(value="select activity.* from service_activity activity " +
            "left join company_info_user cominfo on activity.company_id=cominfo.company_info_user_id" +
            " left  join user_company company on cominfo.company_info_user_id=company.company_info_user_id " +
            " left  join employee employeeen3_ on company.user_company_id=employeeen3_.user_company_id " +
            " left  join user userentity4_  on employeeen3_.user_id=userentity4_.user_id " +
            " where userentity4_.user_id=:userId and employeeen3_.service_management_power=1 and activity.status=:status" +
            " order by activity.gmt_create desc " +
            "limit :startPoint , :endPoint " ,nativeQuery = true)
    List queryByCompanyAndStatus(@Param(value="userId")String userId,@Param(value="status")int status, @Param(value="startPoint")int startPoint, @Param(value="endPoint")int endPoint);

Specification 的用法

下面是个较为全面的例子，将一个较为复杂的查询提取成一个方法。这个方法时使用and的方式拼接，接下来的每一个查询都需要使用把finalConditions拼上，如同 finalConditions = criteriaBuilder.and(finalConditions, taskFastPre)。

public class TaskProjectSpecs {
    public static Specification where(Map params, String userId, List taskIds) {
        //lambda表达式
        return (Root root, CriteriaQuery query, CriteriaBuilder criteriaBuilder) -> {
            //开始
            Predicate finalConditions = criteriaBuilder.conjunction();
            
            //提取参数
            String taskFast = MapUtils.getString(params, "taskFast");

            //lile 和join 用法 join可跟,JoinType.LEFT等
            if (StringUtils.isNotBlank(taskFast)) {
                Predicate taskFastPre = criteriaBuilder.like(root.join("taskType",JoinType.LEFT).get("id"), "%" + taskFast + "%");
                finalConditions = criteriaBuilder.and(finalConditions, taskFastPre);
            }
            //between用法
            if ((null != createBegin) && (null != createEnd)) {
                Predicate datePredicate = null;
                if (createBegin.after(createEnd)) {
                    datePredicate = criteriaBuilder.between(root.get("gmtCreate"), createEnd, createBegin);
                } else {
                    datePredicate = criteriaBuilder.between(root.get("gmtCreate"), createBegin, createEnd);
                }
                finalConditions = criteriaBuilder.and(finalConditions, datePredicate);
            }
            //equale
            if (null != emergency && 0 != emergency) {
                finalConditions = criteriaBuilder.and(finalConditions, criteriaBuilder.equal(root.get("emergencyLevel"), emergency));
            }
            //大于 不等于
            if (status != null) {
                finalConditions = criteriaBuilder.and(finalConditions, criteriaBuilder.greaterThan(root.get("startDate"), new Date()));
                finalConditions = criteriaBuilder.and(finalConditions, criteriaBuilder.notEqual(root.get("status"), 1));
                
            }
            // or 
            if (StringUtils.isNotBlank(keyword)) {
                finalConditions = criteriaBuilder.and(finalConditions, criteriaBuilder.or(
                        criteriaBuilder.like(root.get("taskName"), "%" + keyword + "%"),
                        criteriaBuilder.like(root.join("project").get("name"), "%" + keyword + "%"))
                );
            }
            //in
            if (taskIds.size() > 0) {
                CriteriaBuilder.In