有时我们在查询某个实体的时候,给定的条件是不固定的,这是我们就需要动态 构建相应的查询语句,在JPA2.0中我们可以通过Criteria接口查询,JPA criteria查询.相比JPQL,其优势是类型安全,更加的面向对象.而在Spring data JPA中相应的接口是JpaSpecificationExecutor,这个接口基本是围绕着Specification接口来定义的。 Specification接口中只定义了如下一个方法:
Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb);
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Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb); |
我们只需要重写这个方法即可,相关知识请自行查阅JPA Criteria查询
过滤条件
1:过滤条件会被应用到SQL语句的FROM子句中。在criteria 查询中,查询条件通过Predicate或Expression实例应用到CriteriaQuery对象上。
2:这些条件使用 CriteriaQuery .where 方法应用到CriteriaQuery 对象上
3:CriteriaBuilder也作为Predicate实例的工厂,通过调用CriteriaBuilder 的条件方法( equal,notEqual, gt, ge,lt, le,between,like等)创建Predicate对象。
4:复合的Predicate 语句可以使用CriteriaBuilder的and, or andnot 方法构建。
相关代码如下,在这个例子中我们定义了2个类Articel和User类
Article:
@Entity
@Table(name = "t_article")
public class Article implements Serializable{
private static final long serialVersionUID = 6112067846581696118L;
@Id
@GeneratedValue
private Integer aid;
private String title;
@Temporal(TemporalType.TIMESTAMP)
private Date postTime;
@Temporal(TemporalType.TIMESTAMP)
private Date lastEditTime;
private String ip;
private String tag;
private boolean forbidComment;//禁止评论
@ManyToOne
@JoinColumn(name = "uid")
private User user;
private boolean recommend;//是否是推荐
@Temporal(TemporalType.TIMESTAMP)
private Date recommendTime;//推荐时间
//setter/getter略
}
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@Entity @Table(name = "t_article") public class Article implements Serializable{ private static final long serialVersionUID = 6112067846581696118L; @Id @GeneratedValue private Integer aid; private String title; @Temporal(TemporalType.TIMESTAMP) private Date postTime; @Temporal(TemporalType.TIMESTAMP) private Date lastEditTime; private String ip; private String tag; private boolean forbidComment;//禁止评论 @ManyToOne @JoinColumn(name = "uid") private User user; private boolean recommend;//是否是推荐 @Temporal(TemporalType.TIMESTAMP) private Date recommendTime;//推荐时间 //setter/getter略 } |
User:
@Entity
@Table(name = "t_user")
public class User implements Serializable {
private static final long serialVersionUID = 3703405133265901053L;
@Id
@GeneratedValue
private Integer uid;
private String nickname;
private String password;
//setter/getter略
}
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@Entity @Table(name = "t_user") public class User implements Serializable { private static final long serialVersionUID = 3703405133265901053L; @Id @GeneratedValue private Integer uid; private String nickname; private String password; //setter/getter略 } |
其中user和article是一对多的关系,是单向的
封装的查询实体SearchArticle
public class SearchArticle implements Serializable{
private static final long serialVersionUID = -1082122462716689486L;
private int page = 1;
private int limit;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date postTimeStart;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date postTimeEnd;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date recTimeStart;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date recTimeEnd;
private String nickname;
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public class SearchArticle implements Serializable{ private static final long serialVersionUID = -1082122462716689486L; private int page = 1; private int limit; @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss") private Date postTimeStart; @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss") private Date postTimeEnd; @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss") private Date recTimeStart; @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss") private Date recTimeEnd; private String nickname; |
下面是查询方法
@Autowired
private ArticleRepository articleRepository;
@Override
public QueryResult<ArticleModel> findArticle(SearchArticle
searchArticle) {
Sort sort = new Sort(Sort.Direction.DESC,"postTime");
Specification<Article> specification =
getWhereClause(searchArticle);
Page<Article> all =
articleRepository.findAll(specification, new
PageRequest(searchArticle.getPage() - 1,
searchArticle.getLimit(),sort));
QueryResult<ArticleModel> result = new
QueryResult<>();
List<ArticleModel> list = new
ArrayList<>(searchArticle.getLimit());
for (Article article:all.getContent()){
ArticleModel model = new
ArticleModel(article.getAid(),article.getTitle(),article.getPostTime(),article.isRecommend(),
article.getRecommendTime(),article.getIp(),article.getUser().getUid(),article.getUser().getNickname());
list.add(model);
}
result.setRows(list);
result.setTotal(all.getTotalElements());
return result;
}
/**
* 动态生成where语句
* @param searchArticle
* @return
*/
private Specification<Article> getWhereClause(final
SearchArticle searchArticle){
return new Specification<Article>() {
@Override
public Predicate toPredicate(Root<Article> root,
CriteriaQuery<?> query, CriteriaBuilder cb) {
List<Predicate> predicate = new
ArrayList<>();
if(searchArticle.getPostTimeStart()!=null){
predicate.add(cb.greaterThanOrEqualTo(root.get("postTime").as(Date.class),
searchArticle.getPostTimeStart()));
}
if(searchArticle.getPostTimeEnd()!=null){
predicate.add(cb.lessThanOrEqualTo(root.get("postTime").as(Date.class),
searchArticle.getPostTimeEnd()));
}
if(searchArticle.getRecTimeStart()!=null){
predicate.add(cb.greaterThanOrEqualTo(root.get("recommendTime").as(Date.class),
searchArticle.getRecTimeStart()));
}
if (searchArticle.getRecTimeEnd()!=null){
predicate.add(cb.lessThanOrEqualTo(root.get("recommendTime").as(Date.class),
searchArticle.getRecTimeEnd()));
}
if
(StringUtils.isNotBlank(searchArticle.getNickname())){
//两张表关联查询
Join<Article,User> userJoin =
root.join(root.getModel().getSingularAttribute("user",User.class),JoinType.LEFT);
predicate.add(cb.like(userJoin.get("nickname").as(String.class), "%" +
searchArticle.getNickname() + "%"));
}
Predicate[] pre = new Predicate[predicate.size()];
return
query.where(predicate.toArray(pre)).getRestriction();
}
};
}
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@Autowired private ArticleRepository articleRepository; @Override public QueryResult<ArticleModel> findArticle(SearchArticle searchArticle) { Sort sort = new Sort(Sort.Direction.DESC,"postTime"); Specification<Article> specification = getWhereClause(searchArticle); Page<Article> all = articleRepository.findAll(specification, new PageRequest(searchArticle.getPage() - 1, searchArticle.getLimit(),sort)); QueryResult<ArticleModel> result = new QueryResult<>(); List<ArticleModel> list = new ArrayList<>(searchArticle.getLimit()); for (Article article:all.getContent()){ ArticleModel model = new ArticleModel(article.getAid(),article.getTitle(),article.getPostTime(),article.isRecommend(), article.getRecommendTime(),article.getIp(),article.getUser().getUid(),article.getUser().getNickname()); list.add(model); } result.setRows(list); result.setTotal(all.getTotalElements()); return result; } /** * 动态生成where语句 * @param searchArticle * @return */ private Specification<Article> getWhereClause(final SearchArticle searchArticle){ return new Specification<Article>() { @Override public Predicate toPredicate(Root<Article> root, CriteriaQuery<?> query, CriteriaBuilder cb) { List<Predicate> predicate = new ArrayList<>(); if(searchArticle.getPostTimeStart()!=null){ predicate.add(cb.greaterThanOrEqualTo(root.get("postTime").as(Date.class), searchArticle.getPostTimeStart())); } if(searchArticle.getPostTimeEnd()!=null){ predicate.add(cb.lessThanOrEqualTo(root.get("postTime").as(Date.class), searchArticle.getPostTimeEnd())); } if(searchArticle.getRecTimeStart()!=null){ predicate.add(cb.greaterThanOrEqualTo(root.get("recommendTime").as(Date.class), searchArticle.getRecTimeStart())); } if (searchArticle.getRecTimeEnd()!=null){ predicate.add(cb.lessThanOrEqualTo(root.get("recommendTime").as(Date.class), searchArticle.getRecTimeEnd())); } if (StringUtils.isNotBlank(searchArticle.getNickname())){ //两张表关联查询 Join<Article,User> userJoin = root.join(root.getModel().getSingularAttribute("user",User.class),JoinType.LEFT); predicate.add(cb.like(userJoin.get("nickname").as(String.class), "%" + searchArticle.getNickname() + "%")); } Predicate[] pre = new Predicate[predicate.size()]; return query.where(predicate.toArray(pre)).getRestriction(); } }; } |
其中的 ArticleRepository接口如下,spring data jpa不需要你自己实现dao的接口
public interface ArticleRepository extends JpaRepository<Article,Integer>,JpaSpecificationExecutor<Article> {}
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public interface ArticleRepository extends JpaRepository<Article,Integer>,JpaSpecificationExecutor<Article> {} |
通过以上的步骤,我们就能构建相应的查询sql了,使用这个接口要对JPA2.0中Criteria查询有一定的了解