Spring Data JPA之JpaSpecificationExecutor复杂动态查询实例

本文接SpringDataJPA查询方法那些事继续学习JpaSpecificationExecutor复杂动态查询。

【1】回顾简单查询

简单动态查询实例如下：

 public Page test(){
        Sort sort = new Sort(Sort.Direction.DESC,"id");
        int page = 1;
        int pageSize = 5;
        Pageable pageable = PageRequest.of(page,pageSize,sort);

        //通常使用 Specification 的匿名内部类
        Specification specification = new Specification() {
            /**
             * @param *root: 代表查询的实体类.
             * @param query: 可以从中可到 Root 对象, 即告知 JPA Criteria 查询要查询哪一个实体类. 还可以
             * 来添加查询条件, 还可以结合 EntityManager 对象得到最终查询的 TypedQuery 对象.
             * @param *cb: CriteriaBuilder 对象. 用于创建 Criteria 相关对象的工厂. 当然可以从中获取到 Predicate 对象
             * @return: *Predicate 类型, 代表一个查询条件.
             */
            @Override
            public Predicate toPredicate(Root root,
                                         CriteriaQuery query, CriteriaBuilder cb) {
                Path id = root.get("id");
                Predicate predicateId = cb.gt(id,5);
                return predicateId ;
            }
        };
        Page userPage = userRepository.findAll(specification,  pageable);
        return userPage;
    }

只有一个属性，一个查询条件。

后台打印SQL如下所示：

Hibernate: select user0_.id as id1_1_, user0_.address_id as address_5_1_, user0_.add_id as add_id2_1_,
 user0_.email as email3_1_, user0_.last_name as last_nam4_1_ from tb_user user0_ 
 where user0_.id>5 order by user0_.id desc limit ?, ?
 
Hibernate: select count(user0_.id) as col_0_0_ from tb_user user0_ where user0_.id>5

---

【2】添加多个查询条件

比如这里再添加查询条件：id=5 and email="[email protected]"。

核心方法如下所示：

  Specification specification = new Specification() {
            @Override
            public Predicate toPredicate(Root root,
                                         CriteriaQuery query, CriteriaBuilder cb) {
                Path id = root.get("id");
                Predicate predicateId = cb.gt(id,5);
                Path email = root.get("email");
                Predicate predicateEmail = cb.equal(email, "[email protected]");
                Predicate endPredicate = cb.and(predicateId, predicateEmail);
                return endPredicate;
            }
        };

这里需要用到CriteriaBuilder提供的几个方法：

/**
     * Create a conjunction of the given boolean expressions.
     * @param x  boolean expression
     * @param y  boolean expression
     * @return and predicate
     */
    Predicate and(Expression x, Expression y);
    
    /**
     * Create a conjunction of the given restriction predicates.
     * A conjunction of zero predicates is true.
     * @param restrictions  zero or more restriction predicates
     * @return and predicate
     */
    Predicate and(Predicate... restrictions);

    /**
     * Create a disjunction of the given boolean expressions.
     * @param x  boolean expression
     * @param y  boolean expression
     * @return or predicate
     */
    Predicate or(Expression x, Expression y);

    /**
     * Create a disjunction of the given restriction predicates.
     * A disjunction of zero predicates is false.
     * @param restrictions  zero or more restriction predicates
     * @return or predicate
     */
    Predicate or(Predicate... restrictions);

连词And和OR，其中每种连词又有两种参数。Predicate and(Predicate... restrictions);表示不定数参数Predicate使用And连接起来，通常你可以传入多个Predicate参数，但是建议传入一个数组。

修改上面核心方法如下：

 Specification specification = new Specification() {
            @Override
            public Predicate toPredicate(Root root,
                                         CriteriaQuery query, CriteriaBuilder cb) {
                Path id = root.get("id");
                List predicates=new ArrayList();
                Predicate predicateId = cb.gt(id,5);
                predicates.add(predicateId);
                Path email = root.get("email");
                Predicate predicateEmail = cb.equal(email, "[email protected]");
                predicates.add(predicateEmail);
                Predicate endPredicate = cb.and(predicates.toArray(new Predicate[predicates.size()]));
//                Predicate endPredicate = cb.and((Predicate[]) predicates.toArray());
                return endPredicate;
            }
        };

这里toArray有两种方式：

 Object[] toArray();
  T[] toArray(T[] a);
 
  * 相同点：都是作为数组和collection之间的桥梁；
  * 不同点：toArray()每次都会分配一个新的数组空间，toArray(T[] a);则在某些情况下节省分配成本。

即完整方法如下：

public Page test17(){
        Sort sort = new Sort(Sort.Direction.DESC,"id");
        int page = 1;
        int pageSize = 5;
        Pageable pageable = PageRequest.of(page,pageSize,sort);

        Specification specification = new Specification() {
            @Override
            public Predicate toPredicate(Root root,
                                         CriteriaQuery query, CriteriaBuilder cb) {
                Path id = root.get("id");
                List predicates=new ArrayList();
                Predicate predicateId = cb.gt(id,5);
                predicates.add(predicateId);
                Path email = root.get("email");
                Predicate predicateEmail = cb.equal(email, "[email protected]");
                predicates.add(predicateEmail);
                Predicate endPredicate = cb.and(predicates.toArray(new Predicate[predicates.size()]));
//                Predicate endPredicate = cb.and((Predicate[]) predicates.toArray());
                return endPredicate;
            }
        };
        Page userPage = userRepository.findAll(specification,  pageable);
        return userPage;
    }

此时后台SQL打印如下：

Hibernate: select user0_.id as id1_1_, user0_.address_id as address_5_1_, user0_.add_id as add_id2_1_, 
user0_.email as email3_1_, user0_.last_name as last_nam4_1_ from tb_user user0_ 
where user0_.id>5 and user0_.email=? order by user0_.id desc limit ?, ?

Hibernate: select count(user0_.id) as col_0_0_ from tb_user user0_ where user0_.id>5 and user0_.email=?

---

【3】CriteriaBuilder.conjunction()和CriteriaBuilder.disjunction()

如果没有查询条件呢？即Predicate为null，CriteriaBuilder同样提供了两个方法conjunction()和disjunction()。

方法说明如下;

 /**
     * Create a conjunction (with zero conjuncts).
     * A conjunction with zero conjuncts is true.
     * @return and predicate
     */
    Predicate conjunction();

    /**
     * Create a disjunction (with zero disjuncts).
     * A disjunction with zero disjuncts is false.
     * @return or predicate
     */
    Predicate disjunction();

---

① CriteriaBuilder.conjunction()

修改方法如下所示：

    public Page test(){
        Sort sort = new Sort(Sort.Direction.DESC,"id");
        int page = 1;
        int pageSize = 5;
        Pageable pageable = PageRequest.of(page,pageSize,sort);

        Specification specification = new Specification() {
            @Override
            public Predicate toPredicate(Root root,
                                         CriteriaQuery query, CriteriaBuilder cb) {
                return cb.conjunction();
            }
        };
        Page userPage = userRepository.findAll(specification,  pageable);
        return userPage;
    }

后台SQL打印如下：

Hibernate: select user0_.id as id1_1_, user0_.address_id as address_5_1_, user0_.add_id as add_id2_1_, 
user0_.email as email3_1_, user0_.last_name as last_nam4_1_ from tb_user user0_ 
where 1=1 order by user0_.id desc limit ?, ?

//这里where子句为 where 1=1

Hibernate: select count(user0_.id) as col_0_0_ from tb_user user0_ where 1=1

---

② CriteriaBuilder.disjunction()

修改方法如下所示：

    public Page test18(){
        Sort sort = new Sort(Sort.Direction.DESC,"id");
        int page = 1;
        int pageSize = 5;
        Pageable pageable = PageRequest.of(page,pageSize,sort);

        Specification specification = new Specification() {
            @Override
            public Predicate toPredicate(Root root,
                                         CriteriaQuery query, CriteriaBuilder cb) {
                return cb.disjunction();
//                return cb.conjunction();
            }
        };
        Page userPage = userRepository.findAll(specification,  pageable);
        return userPage;
    }

此时SQL打印如下：

Hibernate: select user0_.id as id1_1_, user0_.address_id as address_5_1_, user0_.add_id as add_id2_1_, 
user0_.email as email3_1_, user0_.last_name as last_nam4_1_ from tb_user user0_ 
where 0=1 order by user0_.id desc limit ?, ?

//这里where子句为 where 0=1，肯定不会返回值了

Hibernate: select count(user0_.id) as col_0_0_ from tb_user user0_ where 0=1

---

【4】Path应用之对象属性为对象

Path是个什么？有三个关键词：对象引用；属性；路径。

源码如下所示：

/**
 * Represents a simple or compound attribute path from a 
 * bound type or collection, and is a "primitive" expression.
 *表示来自绑定类型或集合的简单或复合属性路径，并且是“原语”表达式。

 * @param   the type referenced by the path
 *
 * @since Java Persistence 2.0
 */
public interface Path extends Expression {

    /** 
     * Return the bindable object that corresponds to the path expression.
     */
    Bindable getModel(); 
    
    /**
     *  Return the parent "node" in the path or null if no parent.
     */
    Path getParentPath();
	
    /**
     *  Create a path corresponding to the referenced single-valued attribute.
     */
     Path get(SingularAttribute attribute);

    /**
     *  Create a path corresponding to the referenced collection-valued attribute.
     */
    > Expression get(PluralAttribute collection);

    /**
     *  Create a path corresponding to the referenced map-valued attribute.
     */
    > Expression get(MapAttribute map);

    /**
     *  Create an expression corresponding to the type of the path.
     *  @return expression corresponding to the type of the path
     */
    Expression> type();


    //String-based:
    /**
     *  Create a path corresponding to the referenced attribute.
     */
     Path get(String attributeName);
}

上面使用的属性都是对象的简单属性，如user.id，user.email。但是如果属性为user.address.id呢？

修改方法如下所示：

public Page test(){
        Sort sort = new Sort(Sort.Direction.DESC,"id");
        int page = 1;
        int pageSize = 5;
        Pageable pageable = PageRequest.of(page,pageSize,sort);

        Specification specification = new Specification() {
            @Override
            public Predicate toPredicate(Root root,
                                         CriteriaQuery query, CriteriaBuilder cb) {
                Path