SpringBoot JPA 表关联查询

男娘i 2022-07-15 05:16 330阅读 0赞

### 今天给大家介绍一下如何利用JPA实现表关联查询。 ###

今天给大家举一个一对多的关联查询，并且是使用JPA原生的findBy语句实现的。

想学习**分布式、微服务、JVM、多线程、架构、java、python**的童鞋，千万**不要**扫码，否则后果自负~

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例子中总共有两个实体类，一个是Floor（商品楼层类），另一个是FloorContent（商品楼层内容表）。下面看两张表的源代码：

Floor类：

package cms.model;
    import cms.model.base.BaseDomain;
    import org.hibernate.annotations.GenericGenerator;
    
    import javax.persistence.*;
    import java.io.Serializable;
    import java.util.List;
    /**
     * Created by Roney on 2016/10/10.
     * 楼层管理
     *
     */
    @Entity
    @Table(indexes = {@Index(name = "idx_floor_user",columnList = "user_id")})
    public class Floor extends BaseDomain implements Serializable {
    
        @Id
        @GenericGenerator(name = "PKUUID", strategy = "uuid2")
        @GeneratedValue(generator = "PKUUID")
        @Column(length = 36)
        protected String id;
    
        /**
         * 发布用户ID
         */
        @Column(length = 36,name = "user_id")
        private String userId;
    
        /**
         * 楼层名称
         */
        private String name;
    
        /**
         * 楼层的模板路径
         */
        private String templateUrl;
    
        /**
         * 类型
         * 1.管理端
         * 2.供应商
         */
        private Integer type;
    
    
        /**
         * 排序
         */
        @Column(name = "show_index", nullable = false)
        private Integer showIndex;
    
        /**
         * 是否禁用
         *  */
    
    
        @Column(nullable = false)
        private Boolean isDisable=false;
    
        @OneToMany(fetch = FetchType.LAZY,mappedBy = "floor")
        private List<FloorContent> floorContents;
    
        public List<FloorContent> getFloorContents() {
            return floorContents;
        }
    
        public void setFloorContents(List<FloorContent> floorContents) {
            this.floorContents = floorContents;
        }
    
        public String getId() {
            return id;
        }
    
        public void setId(String id) {
            this.id = id;
        }
    
        public String getUserId() {
            return userId;
        }
    
        public void setUserId(String userId) {
            this.userId = userId;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getTemplateUrl() {
            return templateUrl;
        }
    
        public void setTemplateUrl(String templateUrl) {
            this.templateUrl = templateUrl;
        }
    
        public Integer getShowIndex() {
            return showIndex;
        }
    
        public void setShowIndex(Integer showIndex) {
            this.showIndex = showIndex;
        }
    
        public Boolean getDisable() {
            return isDisable;
        }
    
        public void setDisable(Boolean disable) {
            isDisable = disable;
        }
    
        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
    
            Floor floor = (Floor) o;
    
            return id != null ? id.equals(floor.id) : floor.id == null;
    
        }
    
        @Override
        public int hashCode() {
            return id != null ? id.hashCode() : 0;
        }
    }

FloorContent类：

package cms.model;
    
    import cms.model.base.BaseDomain;
    import org.hibernate.annotations.GenericGenerator;
    
    import javax.persistence.*;
    import java.io.Serializable;
    
    /**
     * Created by Roney on 2016/10/10.
     * 楼层的内容
     */
    
    @Entity
    @Table(indexes = {@Index(name = "idx_floor_content_user", columnList = "user_id")})
    public class FloorContent extends BaseDomain implements Serializable {
    
        @Id
        @GenericGenerator(name = "PKUUID", strategy = "uuid2")
        @GeneratedValue(generator = "PKUUID")
        @Column(length = 36)
        protected String id;
    
        /**
         * 发布用户ID
         */
        @Column(length = 36, name = "user_id")
        private String userId;
    
        /**
         * 內容名稱
         */
        private String name;
    
        /**
         *
         * 內容圖片
         */
        @Column(length = 256)
        private String contentImageUrl;
    
        /**
         * 類型
         * 1.超鏈接
         * 2.圖片檢索
         */
        private Integer type;
    
        /**
         * 超鏈接url
         */
        private  String  linkUrl;
    
        /**
         * 圖片檢索內容
         */
        private String picSearchContent;
    
        /**
         * 排序
         */
        @Column(name = "show_index", nullable = false)
        private Integer showIndex;
    
        /**
         * 是否禁用
         */
    
        @Column(nullable = false)
        private Boolean isDisable = false;
    
        @ManyToOne
        @JoinColumn(name = "floor_id",foreignKey = @ForeignKey(name = "fk_floor_fc"))
        private Floor floor;
    
        public Floor getFloor() {
            return floor;
        }
    
        public void setFloor(Floor floor) {
            this.floor = floor;
        }
    
        public String getId() {
            return id;
        }
    
        public void setId(String id) {
            this.id = id;
        }
    
        public String getUserId() {
            return userId;
        }
    
        public void setUserId(String userId) {
            this.userId = userId;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getContentImageUrl() {
            return contentImageUrl;
        }
    
        public void setContentImageUrl(String contentImageUrl) {
            this.contentImageUrl = contentImageUrl;
        }
    
        public Integer getType() {
            return type;
        }
    
        public void setType(Integer type) {
            this.type = type;
        }
    
        public String getLinkUrl() {
            return linkUrl;
        }
    
        public void setLinkUrl(String linkUrl) {
            this.linkUrl = linkUrl;
        }
    
        public String getPicSearchContent() {
            return picSearchContent;
        }
    
        public void setPicSearchContent(String picSearchContent) {
            this.picSearchContent = picSearchContent;
        }
    
        public Integer getShowIndex() {
            return showIndex;
        }
    
        public void setShowIndex(Integer showIndex) {
            this.showIndex = showIndex;
        }
    
        public Boolean getDisable() {
            return isDisable;
        }
    
        public void setDisable(Boolean disable) {
            isDisable = disable;
        }
    
        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
    
            FloorContent that = (FloorContent) o;
    
            return id != null ? id.equals(that.id) : that.id == null;
    
        }
    
        @Override
        public int hashCode() {
            return id != null ? id.hashCode() : 0;
        }
    }

实体类已经出来了，现在具体说说怎么利用JPA中findBy来实现关联查询：

package cms.model.repository;
    import cms.model.Floor;
    import cms.model.FloorContent;
    import org.springframework.data.domain.Page;
    import org.springframework.data.domain.Pageable;
    import org.springframework.data.jpa.repository.JpaRepository;
    /**
     * Created by Roney on 2016/10/10.
     * Created by Roney on 2016/10/10.
     * 楼层内容管理dao类
     */
    public interface FloorContentRepos extends JpaRepository<FloorContent,String>{
        public Page<FloorContent> findByFloor_IdAndIsDeleteOrderByShowIndexAsc(String floorId,boolean b, Pageable pageable);
    }

从例子中就可以看出JPA关联查询主要在**“\_”**这个符号的使用，下面来给大家具体的介绍一下这个符号到底代表什么含义。

**首先findBy是必须写的，表示使用JPA规则进行查询。**

**如果查询的是本张表中的内容，例如查询本张表中的name字段就可以这么写：findByName()。**

**如果查询的是楼层中的name字段就可以这么写：findByFloor\_Name()。**

**如果是既要查询本张表中的name字段，也要查询楼层中的name字段，就可以这么写：findByFloor\_NameAndName()。**

**从上面的案例就可以看出可以在findBy后面添加要关联的实体类，然后在实体类后面写上“\_”，"\_"符号后面是添加关联表的字段而不是本身表的字段，这点要记住。如何还想关联更多的表可以在后面添加：And+表名字+“\_”+表中要查询的字段。或者只是想关联本身的查询字段可以在后面添加：And+查询的字段。  
千万不要写错了，写错的话运行都运行不起来的。所以写的时候要多看看是否符合规则。**

**如果大家对文章有什么问题或者疑意之类的，可以加我订阅号在上面留言，订阅号上面我会定期更新最新博客。如果嫌麻烦可以直接加我wechat：lzqcode**

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