SpringBoot项目中使用JPA如何实现表关联查询？相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。
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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 floorContents;
public List getFloorContents() {
return floorContents;
}
public void setFloorContents(List 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：