Spring Data JPA 实现多表关联查询

本文地址：https://liuyanzhao.com/6978.html

最近抽出时间来做博客，数据库操作使用的是 JPA，相对比 Mybatis 而言，JPA 单表操作非常方便，增删改查都已经写好了。但是多表操作就不如 Mybatis 那种直接写 sql 语句来得方便，JPA 的多表操作比较麻烦。

需求描述

获得文章列表，文章列表里需要显示每篇文章的分类目录列表，因为一个文章可能有多个分类，一个分类当然也可以对应多篇文章的。

下面是我用截图软件画的一个图，描述的是三张表和其主要字段。

文章表 article 和分类表 category 通过中间表 article_category 关联

我们的需求也很简单，从数据库里查询所有文章，并给每篇文章加一个分类列表的属性。

如图像这样

代码实现

Spring Data JPA 需要的依赖和配置文件这里就不给出了，因为不是本文的重点。

实体类

1、实体类 Article.java

package com.liuyanzhao.blog.entity;
import javax.persistence.*;
import java.io.Serializable;
import java.util.Date;
import java.util.Set;
/**
* @author 言曌
* @date 2017/12/11 下午7:46
*/
@Entity
@Table(name = "article")
public class Article implements Serializable {
private static final long serialVersionUID = 7419229779731522702L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
@Lob//text
@Column(columnDefinition="text")
private String title;
@Lob //longtext
@Column(columnDefinition="longtext")
private String content;
private Integer userId;
private Integer likeCount;
private Date createTime;
private Date updateTime;
private Integer status;
@OneToMany(mappedBy = "article",cascade = CascadeType.ALL, orphanRemoval = true)
private Set<ArticleCategory> articleCategoryList;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public Integer getUserId() {
return userId;
}
public void setUserId(Integer userId) {
this.userId = userId;
}
public Integer getLikeCount() {
return likeCount;
}
public void setLikeCount(Integer likeCount) {
this.likeCount = likeCount;
}
public Date getCreateTime() {
return createTime;
}
public void setCreateTime(Date createTime) {
this.createTime = createTime;
}
public Date getUpdateTime() {
return updateTime;
}
public void setUpdateTime(Date updateTime) {
this.updateTime = updateTime;
}
public Integer getStatus() {
return status;
}
public void setStatus(Integer status) {
this.status = status;
}
public static long getSerialVersionUID() {
return serialVersionUID;
}
public Set<ArticleCategory> getArticleCategoryList() {
return articleCategoryList;
}
public void setArticleCategoryList(Set<ArticleCategory> articleCategoryList) {
this.articleCategoryList = articleCategoryList;
}
}

注意 43-44 行

2、实体类 Category.java

package com.liuyanzhao.blog.entity;
import javax.persistence.*;
import java.io.Serializable;
import java.util.Set;
/**
* @author 言曌
* @date 2017/12/11 下午8:16
*/
@Entity
@Table(name = "category")
public class Category implements Serializable {
private static final long serialVersionUID = 7419229779731522702L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private String name;
private String key;
private Integer status;
@OneToMany(mappedBy = "category")
private Set<ArticleCategory> articleCategoryList;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getStatus() {
return status;
}
public void setStatus(Integer status) {
this.status = status;
}
public String getKey() {
return key;
}
public void setKey(String key) {
this.key = key;
}
public static long getSerialVersionUID() {
return serialVersionUID;
}
public Set<ArticleCategory> getArticleCategoryList() {
return articleCategoryList;
}
public void setArticleCategoryList(Set<ArticleCategory> articleCategoryList) {
this.articleCategoryList = articleCategoryList;
}
}

注意 28-29 行

3、实体类 ArticleCategory.java

package com.liuyanzhao.blog.entity;
import javax.persistence.*;
import java.io.Serializable;
/**
* @author 言曌
* @date 2017/12/12 下午4:08
*/
@Entity
@Table(name = "article_category")
public class ArticleCategory implements Serializable {
private static final long serialVersionUID = 7419229779731522702L;
@Id
@ManyToOne
@JoinColumn(name = "article_id")
private Article article;
@Id
@ManyToOne
@JoinColumn(name = "category_id")
private Category category;
public static long getSerialVersionUID() {
return serialVersionUID;
}
public Article getArticle() {
return article;
}
public void setArticle(Article article) {
this.article = article;
}
public Category getCategory() {
return category;
}
public void setCategory(Category category) {
this.category = category;
}
}

注意 17-25 行

Dao 层

1、ArticleDao.java

package com.liuyanzhao.blog.dao;
import com.liuyanzhao.blog.entity.Article;
import com.liuyanzhao.blog.vo.ArticleVO;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.JpaRepository;
/**
* @author 言曌
* @date 2017/11/28 下午3:31
*/
public interface ArticleDao extends JpaRepository<Article, Integer> {
//获取文章列表，按status和id降序
Page<ArticleVO> findAllByOrderByStatusDescIdDesc(Pageable pageable);
}

2、CategoryDao.java

package com.liuyanzhao.blog.dao;
import com.liuyanzhao.blog.entity.Category;
import org.springframework.data.jpa.repository.JpaRepository;
/**
* @author 言曌
* @date 2017/12/12 上午11:16
*/
public interface CategoryDao extends JpaRepository<Category, Integer> {
}

Service 层

1、ArticleService.java

package com.liuyanzhao.blog.service;
import com.liuyanzhao.blog.vo.ArticleVO;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
/**
* @author 言曌
* @date 2017/12/9 下午4:10
*/
public interface ArticleService {
//获得文章列表
Page<ArticleVO> findAll(Pageable pageable);
}

2、ArticleServiceImpl.java

package com.liuyanzhao.blog.service.Impl;
import com.liuyanzhao.blog.dao.ArticleDao;
import com.liuyanzhao.blog.service.ArticleService;
import com.liuyanzhao.blog.vo.ArticleVO;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.stereotype.Service;
import javax.transaction.Transactional;
/**
* @author 言曌
* @date 2017/12/9 下午4:10
*/
@Service("articleService")
@Transactional
public class ArticleServiceImpl implements ArticleService {
@Autowired
private ArticleDao articleDao;
@Override
public Page<ArticleVO> findAll(Pageable pageable) {
Page<ArticleVO> articleVOPage = articleDao.findAllByOrderByStatusDescIdDesc(pageable);
return articleVOPage;
}
}

Controller 层

ArticleController.java

package com.liuyanzhao.blog.controller;
import com.liuyanzhao.blog.service.ArticleService;
import com.liuyanzhao.blog.vo.ArticleVO;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.ModelAndView;
/**
* @author 言曌
* @date 2017/11/28 下午3:33
*/
@Controller
public class ArticleController {
@Autowired
private ArticleService articleService;
@RequestMapping(value = "/admin/article")
public ModelAndView listUser(@RequestParam(value = "page",defaultValue = "1") Integer page,
@RequestParam(value = "size",defaultValue = "10") Integer size) {
ModelAndView modelAndView = new ModelAndView();
PageRequest request = new PageRequest(page-1,size);
Page<ArticleVO> articleVOPage = articleService.findAll(request);
modelAndView.addObject("articleVOPage",articleVOPage);
modelAndView.setViewName("/admin/article/list");
return modelAndView;
}
}

视图层

视图层主要看表格的打印吧，分页部分和其他内容就不贴出来了

<table class="table table-bordered">
<tr>
<th><input type="checkbox" id="allSelect" onclick="DoCheck()"></th>
<th>ID</th>
<th>作者</th>
<th>标题</th>
<th>分类</th>
<th>更新时间</th>
<th>操作</th>
</tr>
<c:forEach var="article" items="${articleVOPage.content}">
<tr>
<td><input type="checkbox" name="ids" value="${article.id}"></td>
<td>${article.id}</td>
<td>${article.userId}</td>
<td><a href="">${article.title}</a></td>
<td>
<c:forEach var="c" items="${article.articleCategoryList}">
<a href="">${c.category.name}</a>  
</c:forEach>
</td>
<td>${article.updateTime}</td>
<td>
<a href="${pageContext.request.contextPath}/admin/user/profile/${article.id}">
<button type="button" class="btn btn-success btn-xs">查看</button>
</a>
<button type="button" class="btn btn-danger btn-xs"
onclick="deleteUser(${article.id})">删除
</button>
<a href="${pageContext.request.contextPath}/admin/user/edit/${article.id}">
<button type="button" class="btn btn-primary btn-xs">编辑</button>
</a>
</td>
</tr>
</c:forEach>
</table>

最终效果图就是上面的