Springboot-JPA基础内容

2021-02-18 MarsHu springboot springboot

---

• 多环境配置文件(profiles)以及启用方式
• 引入jpa配置,使用实体生成数据库表
• 实体与实体之间一对多关系配置
• JPA的Repository定义
• 双向一对多配置
• 多对多关系配置@ManyToMany
  • 1.单向多对多关系配置
  • 2.双向多对多关系配置
• 禁止JPA创建物理外键
• 使用idea逆向生成Entity
• 自定义JPQL替代JPA命名方法

多环境配置文件(profiles)以及启用方式

假设在resources目录下新建一个配置文件夹config。在config文件夹下新建2个配置类。application-dev.yml和application-prod.yml。

这里需要注意的时,配置文件可以放在resources目录下任意位置,但是命名的规范必须是以application-开头。

application-dev.yml内容如下:

server:
  port: 8081

application-prod.yml内容如下:

server:
  port: 8080

将公共的环境配置放在application.yml中,并且配置需要运行dev还是prod配置,内容如下:

spring:
  profiles:
	#读取dev配置,如果需要读取prod配置,则将dev改成prod
    active: dev

zhqx:
  api-package: com.zhqx.missyou.api

idea中新建的.yml文件没有提示解决

1.点击File->2.点击Project Structure->3.点击Facets->4.点击中间栏目的Spring(项目名)->5.点击右边栏的小树叶(Customize spring boot)

引入jpa配置,使用实体生成数据库表

数据库相关jar包

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-jdbc</artifactId>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>

实体类Banner,相关基于注解的基本配置

package com.zhqx.missyou.model;

import javax.persistence.*;

@Entity
@Table(name = "xm_banner")//指定表名,可以不使用JPA默认表名规则,不使用该注解默认表名为banner
@Where(clause = "delete_time is null")//指定查询条件
public class Banner {
    @Id//指定主键
	@GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    @Column(length = 16)//设置字段长度
    private String name;
    @Transient//不生成该名称对应的表字段
    private String description;
    private String img;
    private String title;
}

jpa相关配置application.yml:

spring:
  profiles:
    active: dev
  jpa:
    hibernate:
      ddl-auto: create-drop #实际开发中建议使用update

zhqx:
  api-package: com.zhqx.missyou.api

实体与实体之间一对多关系配置

新建一个实体类BannerItem

package com.zhqx.missyou.model;

import javax.persistence.*;

@Entity
public class BannerItem {
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    private String img;
    private String keyword;
    private Short type;
    private String name;
}

一个Banner可以对应多个BannerItem.在Banner中添加BannerItem集合属性

package com.zhqx.missyou.model;

import javax.persistence.*;
import java.util.List;

@Entity
public class Banner {
    @Id//指定主键
	@GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    @Column(length = 16)//设置字段长度
    private String name;
    @Transient//不生成该名称对应的表字段
    private String description;
    private String img;
    private String title;
    
    @OneToMany
    private List<BannerItem> items;
}

此时,运行程序,程序会自动生成三张表。banner、banner_item、banner_items。其中banner_items表中有2个字段.banner_id和items_id。 这个关系是由JPA默认建表规则生成。

因为在当前的banner_item表中没有字段表示属于哪一个banner,所有JPA才会自动生成第三张表来维护之间的关系。为了避免自动生成第三张表。 我们需要在BannerItem中新增一个字段bannerId表示外键关系。

package com.zhqx.missyou.model;

import javax.persistence.*;

@Entity
public class BannerItem {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    private String img;
    private String keyword;
    private Short type;
    private String name;
	//这里JPA默认创建的表字段名为banner_id
    private Long bannerId;
}

同时我们需要在Banner中指定要关联的外键字段

package com.zhqx.missyou.model;

import javax.persistence.*;
import java.util.List;

@Entity
public class Banner {
    @Id//指定主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    @Column(length = 16)//设置字段长度
    private String name;
    @Transient//不生成该名称对应的表字段
    private String description;
    private String img;
    private String title;

    @OneToMany
    @JoinColumn(name = "bannerId")
    private List<BannerItem> items;
}

此时,运行程序,就不会创建第三张表了,需要注意的是,此时banner表和banner_item表是存在物理外键的。

JPA的Repository定义

定义JPA查询接口

package com.zhqx.missyou.repository;

import com.zhqx.missyou.model.Banner;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface BannerRepository extends JpaRepository<Banner, Long> {
    //JpaRepository<T, ID> T表示业务对象,ID表示主键的类型
    
    Banner findOneById(Long id);
    Banner findOneByName(String name);
}

在service中调用:

package com.zhqx.missyou.service;

import com.zhqx.missyou.model.Banner;

public interface BannerService {
        Banner getByName(String name);
}
==========================================
package com.zhqx.missyou.service.impl;

import com.zhqx.missyou.model.Banner;
import com.zhqx.missyou.repository.BannerRepository;
import com.zhqx.missyou.service.BannerService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class BannerServiceImpl implements BannerService {

    @Autowired
    private BannerRepository bannerRepository;

    @Override
    public Banner getByName(String name) {
        return bannerRepository.findOneByName(name);
    }
}

在控制器中调用:

package com.zhqx.missyou.api.v1;

import com.zhqx.missyou.model.Banner;
import com.zhqx.missyou.service.BannerService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.validation.annotation.Validated;
        import org.springframework.web.bind.annotation.*;

        import javax.validation.constraints.NotBlank;

@RestController
@RequestMapping("/banner")
@Validated
public class BannerController {

    @Autowired
    private BannerService bannerService;

    @GetMapping("/name/{name}")
    public Banner getByName(@PathVariable @NotBlank String name) {
        Banner banner = bannerService.getByName(name);
        return banner;
    }
}

这里需要注意的是不要忘了补全Banner和BannerItem实体中的getter和setter方法,否则会出现返回结果为null的问题。因为使用了lombok插件。 所以分别在两个实体上加上@Getter和@Setter注解

打印SQL,并且格式化输出SQL配置,application-dev.yml中配置

server:
  port: 8080
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/missyou?characterEncoding=utf-8&serverTimezone=GMT%2B8
    username: root
    password: root
  jpa:
    show-sql: true
    properties:
      hibernate:
        format_sql: true

在默认情况下JPA的一对多查询是一种惰性查询模式(懒加载模式),如果没有用到items属性时,是不会执行关联查询的。当然我们也可以要求在初始时, 就默认查出关联的items。使用注解@OneToMany(fetch = FetchType.EAGER)

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;
import java.util.List;

@Getter
@Setter
@Entity
@Table(name = "banner")//指定表名
public class Banner {
    @Id//指定主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    @Column(length = 16)//设置字段长度
    private String name;
    @Transient//不生成该名称对应的表字段
    private String description;
    private String img;
    private String title;

    @OneToMany(fetch = FetchType.EAGER)//初始时,就关联查询出数据
    @JoinColumn(name = "bannerId")
    private List<BannerItem> items;
}

如果需要测试这种情况,只需要将控制器中返回结果改为void,然后测试使用该注解和不使用该注解时,观察控制台打印内容就可以了。当然正常情况下,我们还是不要修改默认的惰性查询机制。

双向一对多配置

在当前的配置中,我们可以通过banner查询出关联的bannerItem,如果我想通过bannerItem查询出关联的banner应该怎么做呢,这个时候就需要用到 双向一对多的配置。

修改BannerItem,增加关联属性banner,同时将原来的@JoinColumn注解使用在当前属性上

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;

@Getter
@Setter
@Entity
public class BannerItem {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    private String img;
    private String keyword;
    private Short type;
    private String name;

    private Long bannerId;

    @ManyToOne
    @JoinColumn(name = "bannerId")
    private Banner banner;
}

修改Banner,指定双向绑定的属性是什么,此案例中是banner,同时删除注解@JoinColumn

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;
import java.util.List;

@Getter
@Setter
@Entity
@Table(name = "banner")//指定表名
public class Banner {
    @Id//指定主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    @Column(length = 16)//设置字段长度
    private String name;
    @Transient//不生成该名称对应的表字段
    private String description;
    private String img;
    private String title;

    @OneToMany(mappedBy = "banner", fetch = FetchType.EAGER)
    private List<BannerItem> items;
}

双向一对多的配置后,原来的bannerId就没有必要存在了,JPA规则中配置了双向一对多后,会自动生成banner_item,并生成外键。运行程序会出错, 需要我们将BannerItem中的bannerId属性给删除。

但是在实际开发过程中,我们有的时候是需要这个值的,所以我们需要进一步配置.

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;

@Getter
@Setter
@Entity
public class BannerItem {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    private String img;
    private String keyword;
    private Short type;
    private String name;

    private Long bannerId;

    @ManyToOne
    @JoinColumn(insertable = false, updatable = false, name = "bannerId")
    private Banner banner;
}

JPA默认双向一对多会自动生成外键物理字段banner_id,不利于值的获取,实际开发过程中可以选择性的使用单向一对多的配置。或者使用双向一对多时,使用上面的配置来解决。

多对多关系配置@ManyToMany

1.单向多对多关系配置

Theme类:

package com.zhqx.missyou.model;

import javax.persistence.Entity;
import javax.persistence.ManyToMany;
import java.util.List;

@Entity
public class Theme {
	@Id
    private Long id;
    private String title;
    private String name;

    @ManyToMany
    private List<Spu> spuList;
}

Spu类:

package com.zhqx.missyou.model;

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Spu {
    @Id
    private Long id;
    private String title;
    private String subtitle;

}

此时,JPA默认生成三张表:spu、theme、theme_spu_list。首先默认的情况下我们希望生成theme_spu表而不是后面加上一个list。而且在默认生成的theme_spu_list表中维护的外键字段是spu_list_id,实际上我们只需要生成spu_id这样的字段。

所以我们需要指定第三张表的名称以及相关外键字段名称。

package com.zhqx.missyou.model;

import javax.persistence.*;
import java.util.List;

@Entity
public class Theme {
    @Id
    private Long id;
    private String title;
    private String name;

    @ManyToMany
    @JoinTable(name = "theme_spu", joinColumns = @JoinColumn(name = "theme_id"),
    inverseJoinColumns = @JoinColumn(name = "spu_id"))
    private List<Spu> spuList;
}

2.双向多对多关系配置

在一对多关系中,一方表示被维护端,多方表示维护端。双向多对多关系,我们需要确定一个双向关系的维护端,我们让Spu成为关系的被维护端。

修改Spu类,指定多对多的属性(该属性对应Theme类的spuList属性):

package com.zhqx.missyou.model;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import java.util.List;

@Entity
public class Spu {
    @Id
    private Long id;
    private String title;
    private String subtitle;
    
    @ManyToMany(mappedBy = "spuList")
    private List<Theme> themeList;
}

禁止JPA创建物理外键

1.在Banner类中使用注解@org.hibernate.annotations.ForeignKey

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;
import java.util.List;

@Getter
@Setter
@Entity
@Table(name = "banner")//指定表名
public class Banner {
    @Id//指定主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    @Column(length = 16)//设置字段长度
    private String name;
    @Transient//不生成该名称对应的表字段
    private String description;
    private String img;
    private String title;

    @OneToMany(mappedBy = "banner", fetch = FetchType.EAGER)
    @org.hibernate.annotations.ForeignKey(name = "null")
    private List<BannerItem> items;
}

2.在BannerItem配置,有BUG

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;

@Getter
@Setter
@Entity
public class BannerItem {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长
    private Long id;
    private String img;
    private String keyword;
    private Short type;
    private String name;

    private Long bannerId;

    @ManyToOne
    @JoinColumn(foreignKey = @ForeignKey(value = ConstraintMode.NO_CONSTRAINT),insertable = false, updatable = false, name = "bannerId")
    private Banner banner;
}

使用idea逆向生成Entity

使用的idea版本,2018.3.6.依次点击View->Tool Windows->Database

在弹出的Database窗口,点击+号->Data Source->Mysql.

在弹出的DataSources And Drivers窗口中,填写Database、user、password、host等信息。然后点击Apply,再点击OK,这有右边就会出现数据库连接窗口。

点击File->Project Structure->Modules->点击+号->选择JPA。

将Default JPA Provider修改为Hibernate,点击Apply,再点击OK。

View->Tool Windows->Persistence。在弹出的窗口中,点击missyou,右键->Generate Persistence Mapping->By DataBase Schema

在弹出的Import Database Schema窗口中依次设置Choose Data Source、以及需要将生成的Entity放在哪个Package。本案例中选择:com.zhqx.missyou.model

将Entity suffix里的后缀删除。

勾选需要生成的表,这里以banner表为例,然后点击OK,点击YES.生成的实体如下:

package com.zhqx.missyou.model;

import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import java.sql.Timestamp;
import java.util.Objects;

@Entity
public class Banner {
    private int id;
    private String name;
    private String description;
    private Timestamp createTime;
    private Timestamp updateTime;
    private Timestamp deleteTime;
    private String title;
    private String img;

    @Id
    @Column(name = "id")
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Basic
    @Column(name = "name")
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Basic
    @Column(name = "description")
    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    @Basic
    @Column(name = "create_time")
    public Timestamp getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Timestamp createTime) {
        this.createTime = createTime;
    }

    @Basic
    @Column(name = "update_time")
    public Timestamp getUpdateTime() {
        return updateTime;
    }

    public void setUpdateTime(Timestamp updateTime) {
        this.updateTime = updateTime;
    }

    @Basic
    @Column(name = "delete_time")
    public Timestamp getDeleteTime() {
        return deleteTime;
    }

    public void setDeleteTime(Timestamp deleteTime) {
        this.deleteTime = deleteTime;
    }

    @Basic
    @Column(name = "title")
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    @Basic
    @Column(name = "img")
    public String getImg() {
        return img;
    }

    public void setImg(String img) {
        this.img = img;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Banner banner = (Banner) o;
        return id == banner.id &&
                Objects.equals(name, banner.name) &&
                Objects.equals(description, banner.description) &&
                Objects.equals(createTime, banner.createTime) &&
                Objects.equals(updateTime, banner.updateTime) &&
                Objects.equals(deleteTime, banner.deleteTime) &&
                Objects.equals(title, banner.title) &&
                Objects.equals(img, banner.img);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name, description, createTime, updateTime, deleteTime, title, img);
    }
}

实际上默认生成的实体,有时候可能不太符合开发习惯.我们可以进行修改一下。调整后的Banner、BannerItem、BaseEntity数据如下:

Banner类:

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;
import java.util.List;

@Getter
@Setter
@Entity
public class Banner extends BaseEntity {
    @Id
    private Long id;
    private String name;
    private String description;
    private String title;
    private String img;

    @OneToMany(fetch = FetchType.LAZY)
    @JoinColumn(name = "bannerId")
    private List<BannerItem> items;
}

BannerItem类:

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;

@Getter
@Setter
@Entity
public class BannerItem extends BaseEntity{
    @Id
    private Long id;
    private String img;
    private String keyword;
    private short type;
    private Long bannerId;
    private String name;

}

BaseEntity类:

package com.zhqx.missyou.model;

import lombok.Getter;
import lombok.Setter;

import java.util.Date;

@Getter
@Setter
public abstract class BaseEntity {
    private Date createTime;
    private Date updateTime;
    private Date deleteTime;
}

自定义JPQL替代JPA命名方法

ThemeRepository类:

package com.zhqx.missyou.repository;

import com.zhqx.missyou.model.Theme;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;

import java.util.List;
import java.util.Optional;

@Repository
public interface ThemeRepository extends JpaRepository<Theme, Long> {

    @Query("select t from Theme t where t.name in (:names)")
    List<Theme> findByNames(@Param("names") List<String> names);

}

这里如果@Param(“names”)中的名字是什么,则在(:names)中的名字应该与之对应。

原文链接: https://marshucheng1.github.io/2021/02/18/springboot-qiyue-4/

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