《从零打造项目》系列文章
工具
- 比MyBatis Generator更强大的代码生成器
ORM框架选型
SpringBoot项目基础设施搭建
SpringBoot集成Mybatis项目实操
SpringBoot集成MybatisPlus项目实操
SpringBoot集成Spring Data JPA项目实操
前言
该说的在《SpringBoot集成Mybatis项目实操》一文中都讲了，本文只是将 Mybatis 换成了 Spring Data JPA，带大家将整个项目跑起来。
本文将实现 SpringBoot+ Spring Data JPA 的项目搭建，项目特色是针对 JPA 专门写了一套动态链式查询工具类，进而实现一对多查询和连表查询。
不说废话了，我们直接进入主题。
数据库
本项目采用的是 MySQL 数据库，版本为 8.x，建表语句如下：
CREATE TABLE `customer` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`age` int(11) DEFAULT NULL,
`address` varchar(100) DEFAULT NULL,
`created_date` timestamp NULL DEFAULT NULL,
`last_modified_date` timestamp NULL DEFAULT NULL,
`del_flag` int(2) NOT NULL DEFAULT '0',
`create_user_name` varchar(50) DEFAULT NULL,
`last_modified_name` varchar(50) DEFAULT NULL,
`version` int(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`),
UNIQUE KEY `uk_name` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='父用户';
CREATE TABLE `subUser` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`customer_id` varchar(36) NOT NULL,
`address` varchar(100) DEFAULT NULL,
`created_date` timestamp NULL DEFAULT NULL,
`last_modified_date` timestamp NULL DEFAULT NULL,
`del_flag` int(2) NOT NULL DEFAULT '0',
`create_user_name` varchar(50) DEFAULT NULL,
`last_modified_name` varchar(50) DEFAULT NULL,
`version` int(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='子用户';
搭建SpringBoot项目
使用 IDEA 新建一个 Maven 项目，叫做 jpa-springboot。
一些共用的基础代码可以参考上篇文章，这里不做重复介绍，会介绍一些 JPA 相关的代码。
引入依赖
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.6.3</version>
</parent>
<properties>
<java.version>1.8</java.version>
<fastjson.version>1.2.73</fastjson.version>
<hutool.version>5.5.1</hutool.version>
<mysql.version>8.0.19</mysql.version>
<mybatis.version>2.1.4</mybatis.version>
<mapper.version>4.1.5</mapper.version>
<org.mapstruct.version>1.4.2.Final</org.mapstruct.version>
<org.projectlombok.version>1.18.20</org.projectlombok.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-aop</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-validation</artifactId>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>${fastjson.version}</version>
</dependency>
<dependency>
<groupId>cn.hutool</groupId>
<artifactId>hutool-all</artifactId>
<version>${hutool.version}</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>${org.projectlombok.version}</version>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>${mysql.version}</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>${mybatis.version}</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springdoc</groupId>
<artifactId>springdoc-openapi-ui</artifactId>
<version>1.6.9</version>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
<version>1.1.18</version>
</dependency>
<dependency>
<groupId>org.mapstruct</groupId>
<artifactId>mapstruct</artifactId>
<version>${org.mapstruct.version}</version>
</dependency>
<dependency>
<groupId>org.mapstruct</groupId>
<artifactId>mapstruct-processor</artifactId>
<version>${org.mapstruct.version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
有些依赖不一定是最新版本，而且你看到这篇文章时，可能已经发布了新版本，到时候可以先模仿着将项目跑起来后，再根据自己的需求来升级各项依赖，有问题咱再解决问题。
分页处理
某些业务场景是需要分页查询和排序功能的，所以我们需要考虑前端如何传递参数给后端，后端如何进行分页查询或者是排序查询。JPA 分页查询使用的是 Spring 自带的 Pageable。
分页基础类
public class SimplePageInfo {
private Integer pageNum = 1;
private Integer pageSize = 10;
public Integer getPageNum() {
return pageNum;
}
public void setPageNum(Integer pageNum) {
this.pageNum = pageNum;
}
public Integer getPageSize() {
return pageSize;
}
public void setPageSize(Integer pageSize) {
this.pageSize = pageSize;
}
}
排序包装类
@Getter
@Setter
public class OrderInfo {
private boolean asc = true;
private String column;
}
分页且排序包装类
@Getter
@Setter
@EqualsAndHashCode(callSuper = true)
public class PageSortInfo extends SimplePageInfo {
@Schema(name = "排序信息")
private List<OrderInfo> orderInfos;
public String parseSort() {
if (CollectionUtils.isEmpty(orderInfos)) {
return null;
}
StringBuilder sb = new StringBuilder();
for (OrderInfo orderInfo : orderInfos) {
sb.append(orderInfo.getColumn()).append(" ");
sb.append(orderInfo.isAsc() ? " ASC," : " DESC,");
}
sb.deleteCharAt(sb.length() - 1);
return sb.toString();
}
}
前端分页查询的请求体对象
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class CustomerQueryPageDTO {
@JsonUnwrapped
private PageSortInfo pageSortInfo;
}
服务层分页查询
Pageable pageable = SpecificationBuilder.getPageable(dto.getPageSortInfo());
Page<Customer> customerPage = customerRepository.findAll(pageable);
关于 PageHelper 的使用这里就不多做介绍了。
我们得到的分页查询结果是 Page 对象，可以直接使用，也可以根据需要进行修改，比如下面这个文件：
@Getter
@Setter
public class PageResult<T> {
/**
* 总条数
*/
private Long total;
/**
* 总页数
*/
private Integer pageCount;
/**
* 每页数量
*/
private Integer pageSize;
/**
* 当前页码
*/
private Integer pageNum;
/**
* 分页数据
*/
private List<T> data;
/**
* 处理Jpa分页结果，Jpa页码默认从0开始，所以返回结果加1
*/
public static <T> PageResult<T> ok(org.springframework.data.domain.Page<T> page) {
PageResult<T> result = new PageResult<T>();
result.setPageCount(page.getTotalPages());
result.setPageNum(page.getNumber() + 1);
result.setPageSize(page.getSize());
result.setTotal(page.getTotalElements());
result.setData(page.getContent());
return result;
}
}
JPA基础实体类
作为其他实体类的父类，封装了所有的公共字段，包括逻辑删除标志，版本号，创建人和修改人信息。到底是否需要那么多字段，结合实际情况，这里的示例代码比较全，其中@LogicDelete 和@Version 是 Mybatis 特有的注解，@CreatedBy、@CreatedDate 是Springframework 自带的注解，如果我们需要新建人和修改人姓名，则需要自定义注解。
@MappedSuperclass
@EntityListeners(AuditingEntityListener.class)
@Getter
@EqualsAndHashCode(of = "id")
@SuperBuilder(toBuilder = true)
@NoArgsConstructor
@AllArgsConstructor
public class BaseDomain implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Schema(name = "创建人姓名")
@CreatedBy
@Column(name = "create_user_name")
private String createUserName;
@CreatedDate
private LocalDateTime createdDate;
@LastModifiedBy
@Schema(name = "修改人姓名")
@Column(name = "last_modified_name")
private String lastModifiedName;
@LastModifiedDate
private LocalDateTime lastModifiedDate;
@Schema(name = "")
@Column(name = "del_flag")
private Integer delFlag = 0;
@Schema(name = "版本号")
@Version
@Column(name = "version")
private Integer version;
}
可以发现，相较于 Mybatis 和 MybatisPlus 少了两个字段，分别是 createUserCode 和 lastModifiedCode，因为 Spring 提供的注解只有 CreatedBy 和 LastModifiedBy，我们可以基于 Spring Data 的 AuditorAware 审计功能来给这两个注解标识的字段赋值。
JPA审计
简单介绍一下审计功能：即由谁在什么时候创建或修改实体。Spring Data 提供了在实体类的属性上增加@CreatedBy，@LastModifiedBy，@CreatedDate，@LastModifiedDate 注解，并配置相应的配置项，即可实现审计功能，有系统自动记录createdBy 、CreatedDate 、lastModifiedBy 、lastModifiedDate四个属性的值。
所以如果在 AuditorAware 实现类中根据@CreatedBy 拿到的值去数据库中查询 userCode 信息，也不是不可以，这里项目比较简单，所以就不过多介绍了。
@Configuration
public class JpaAutoConfiguration implements AuditorAware<String> {
@Override
public Optional<String> getCurrentAuditor() {
SecurityContext ctx = SecurityContextHolder.getContext();
Object principal = ctx.getAuthentication().getPrincipal();
if (principal.getClass().isAssignableFrom(String.class)) {
return Optional.of((String) principal);
} else {
return Optional.empty();
}
}
}
因为我们没有使用 SpringSecurity 来配置 token 信息，所以这里获取的 principal 是默认值，值为 anonymousUser。
动态链式查询
利用 JPA 的Specification<T>接口和元模型就实现动态查询，相较于这篇文章，本文实现借鉴了 Mybatis 中使用的 ExampleBuilder，个人觉得效果更佳。
1、查询关系匹配枚举
public enum MatchCondition {
/**
* equal-相等，notEqual-不等于，like-模糊匹配，notLike-， gt-大于，ge-大于等于，lt-小于，le-小于等于
*/
EQUAL,
NOT_EQUAL,
LIKE,
NOT_LIKE,
GT,
GE,
LT,
LE,
IN,
NOT_IN,
BETWEEN,
NOT_BETWEEN
}
2、查询条件连接符枚举
public enum Operator {
AND,
OR
}
3、查询条件注解
@Target({ElementType.FIELD, ElementType.CONSTRUCTOR})
@Retention(RetentionPolicy.RUNTIME)
public @interface QueryCondition {
/**
* 数据库中字段名,默认为空字符串,则Query类中的字段要与数据库中字段一致
*/
String column() default "";
/**
* @see MatchCondition
*/
MatchCondition func() default MatchCondition.EQUAL;
}
4、连接符枚举
public enum Connector {
ON,
WHERE
}
5、查询条件包装类
//理论上会有多个QueryParam对象，当Connector是where时，joinName和joinType为null，当Connector为on时，根据joinName的不同，会生成不同的QueryParam对象，joinType包括INNER、LEFT
@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class QueryParam {
private Connector connector;
private List<QueryItem> queryItems;
private String joinName;
private JoinType joinType;
}
@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class QueryItem {
private String fieldName;
private Object fieldValue;
private MatchCondition matchCondition;
// between使用
private Object startValue;
private Object endValue;
// in查询
private Iterable<Object> iterable;
private Operator operator;
}
6、集成工具类
因代码篇幅受限，就只粘贴部分代码：
public SpecificationBuilder<T> andEqualTo(IFn<T, Object> fn, Object value) {
QueryItem queryItem = QueryItem.builder().fieldName(Reflections.fnToFieldName(fn))
.fieldValue(value).operator(Operator.AND).matchCondition(
MatchCondition.EQUAL).build();
addQueryItemToWhereParam(queryItem);
return this;
}
private void addQueryItemToWhereParam(QueryItem queryItem) {
if (CollectionUtils.isEmpty(queryParams)) {
queryParams.add(addQueryItem(queryItem));
} else {
Optional<QueryParam> queryParamOptional = queryParams.stream()
.filter(obj -> StringUtils.isEmpty(obj.getJoinName())).findFirst();
if (queryParamOptional.isPresent()) {
QueryParam queryParam = queryParamOptional.get();
queryParam.getQueryItems().add(queryItem);
} else {
queryParams.add(addQueryItem(queryItem));
}
}
}
相较于 Mybatis 项目中的 ExampleBuilder，SpecificationBuilder 仅用于查询功能，暂时无法提供修改，删除等功能，不过也有自己的额特色：可以实现连表查询，比如说 left join 等，以及懒加载问题，避免连表查询时出现的 N+1 查询。
至此，关于本项目中有价值的内容已经讲述完毕，因篇幅有限，未能展示所有代码。基于上述核心代码，我们只需要往项目中添加相关业务代码即可，接下来我们就可以运行之前写的脚本工具，根据数据库表信息快速生成模板代码。
一键式生成模版代码
运行 orm-generate 项目，在 swagger 上调用 /build 接口，调用参数如下：
{
"database": "mysql_db",
"flat": true,
"type": "jpa",
"group": "hresh",
"host": "127.0.0.1",
"module": "orm",
"password": "root",
"port": 3306,
"table": [
"customer",
"sub_user"
],
"username": "root",
"tableStartIndex":"0"
}
代码文件直接移到项目中就行了，稍微修改一下引用就好了。
功能实现
请求日志输出
比如说我们访问 customers/queryPage 接口，看看控制台输出情况：
Request Info : {"classMethod":"com.msdn.orm.hresh.controller.CustomerController.queryPage","ip":"127.0.0.1","requestParams":{"dto":{"pageSortInfo":{"count":true,"pageSize":5,"orderInfos":[{"column":"name","asc":true}],"pageNum":1}}},"httpMethod":"GET","url":"http://localhost:8803/customers/queryPage","result":{"code":"200","message":"操作成功","success":true},"methodDesc":"获取父用户分页列表","timeCost":268}
可以看到，日志输出中包含前端传来的请求体，请求 API，返回结果，API 描述，API 耗时。
统一返回格式
比如说分页查询，返回结果如下：
{
"data": {
"total": 9,
"pageCount": 2,
"pageSize": 5,
"pageNum": 1,
"data": [
{
"name": "acorn",
"age": 38,
"address": "湖北武汉"
},
{
"name": "acorn2",
"age": 28,
"address": "湖北武汉"
},
{
"name": "hresh",
"age": 44,
"address": "湖北武汉"
},
{
"name": "love0",
"age": 26,
"address": "湖北武汉"
},
{
"name": "love1",
"age": 26,
"address": "湖北武汉"
}
]
},
"code": "200",
"message": "操作成功",
"success": true
}
如果是新增请求，返回结果为：
{
"data": {
"name": "rookie3",
"age": 26,
"address": "湖北武汉"
},
"code": "200",
"message": "操作成功",
"success": true
}
异常处理
下面简单演示一下参数异常的情况，在 add user 时校验参数值是否为空。
public CustomerVO add(CustomerDTO dto) {
if (StringUtils.isBlank(dto.getName())) {
BusinessException.validateFailed("userName不能为空");
}
Customer customer = customerRepository.save(customerStruct.dtoToModel(dto));
return customerStruct.modelToVO(customer);
}
如果传递的 name 值为空，则返回结果为：
{
"data": null,
"code": "400",
"message": "userName不能为空",
"success": false
}
分组校验和自定义校验
修改 CustomerDTO，当新增数据时，校验 name 不为空，修改数据时，address 不为空。
public class CustomerDTO {
@NotBlank(groups = {Add.class})
@Schema(name = "")
private String name;
@EnumValidator(value = {"18", "20", "24"}, message = "age只能指定为18、20和24，其他值不合法")
@Schema(name = "")
private Integer age;
@NotBlank(groups = {Update.class})
@Schema(name = "")
private String address;
}
最后修改 controller 文件
@PostMapping
@Operation(description = "新增父用户")
public Result<CustomerVO> add(@Validated(Add.class) @RequestBody CustomerDTO dto) {
CustomerVO customerVO = customerService.add(dto);
return Result.ok(customerVO);
}
调用新增接口，故意将 name 置为空，返回结果为：
{
"data": null,
"code": "400",
"message": "name不能为空",
"success": false
}
如果 age 不为 18、20和24，则出现如下错误：
{
"data": null,
"code": "400",
"message": "ageage只能指定为18、20和24，其他值不合法",
"success": false
}
批量操作
这里简单演示一下关于批量新增的代码
public void batchAdd(CustomerDTO dto) {
List<Customer> customers = new ArrayList<>();
for (int i = 0; i < 3; i++) {
Customer customer = new Customer();
customer.setName(dto.getName() + i);
customer.setAge(dto.getAge());
customer.setAddress(dto.getAddress());
customers.add(customer);
}
customerRepository.saveAll(customers);
}
注意，delFlag 没有对应的注解，所以只能手动赋值为 0，否则插入数据时会报错。
执行效果如下：
分页查询
前端参数传递：
{
"pageNum": 1,
"pageSize": 5,
"orderInfos":[
{
"column": "name",
"asc": true
}
]
}
后端代码处理：
public Page<CustomerVO> queryPage(CustomerQueryPageDTO dto) {
Pageable pageable = SpecificationBuilder.getPageable(dto.getPageSortInfo());
Page<Customer> customerPage = customerRepository.findAll(pageable);
return customerPage.map(customer -> customerStruct.modelToVO(customer));
}
返回结果为：
{
"data": {
"total": 9,
"pageCount": 2,
"pageSize": 5,
"pageNum": 1,
"data": [
{
"name": "acorn",
"age": 38,
"address": "湖北武汉"
},
{
"name": "acorn2",
"age": 28,
"address": "湖北武汉"
},
{
"name": "hresh",
"age": 44,
"address": "湖北武汉"
},
{
"name": "love0",
"age": 26,
"address": "湖北武汉"
},
{
"name": "love1",
"age": 26,
"address": "湖北武汉"
}
]
},
"code": "200",
"message": "操作成功",
"success": true
}
动态查询
查询方法如下：
public List<CustomerVO> queryList(CustomerDTO dto) {
List<Customer> customers = SpecificationBuilder.create(CustomerRepository.class)
.andLike(Customer::getName, dto.getName() + "%")
.select();
return customerStruct.modelToVO(customers);
}
执行结果如下：
{
"data": [
{
"name": "rookie",
"age": 26,
"address": "湖北武汉"
},
{
"name": "rookie1",
"age": 26,
"address": "湖北武汉"
},
{
"name": "rookie2",
"age": 26,
"address": "湖北武汉"
},
{
"name": "rookie3",
"age": 26,
"address": "湖北武汉"
}
],
"code": "200",
"message": "操作成功",
"success": true
}
SQL 输出为：
select customer0_.id as id1_0_, customer0_.create_user_name as create_u2_0_, customer0_.created_date as created_3_0_, customer0_.del_flag as del_flag4_0_, customer0_.last_modified_date as last_mod5_0_, customer0_.last_modified_name as last_mod6_0_, customer0_.version as version7_0_, customer0_.address as address8_0_, customer0_.age as age9_0_, customer0_.name as name10_0_ from customer customer0_ where ( customer0_.del_flag=0) and (customer0_.name like ?)
如果是分页查询，可以这样处理：
public Page<CustomerVO> queryPage(CustomerQueryPageDTO dto) {
Pageable pageable = SpecificationBuilder.getPageable(dto.getPageSortInfo());
Page<Customer> customerPage = SpecificationBuilder.create(CustomerRepository.class)
.andLike(Customer::getName, dto.getName() + "%")
.select(pageable);
// Page<Customer> customerPage = customerRepository.findAll(pageable);
return customerPage.map(customer -> customerStruct.modelToVO(customer));
}
查询结果为：
{
"data": {
"total": 4,
"pageCount": 1,
"pageSize": 5,
"pageNum": 1,
"data": [
{
"name": "rookie",
"age": 26,
"address": "湖北武汉"
},
{
"name": "rookie1",
"age": 26,
"address": "湖北武汉"
},
{
"name": "rookie2",
"age": 26,
"address": "湖北武汉"
},
{
"name": "rookie3",
"age": 26,
"address": "湖北武汉"
}
]
},
"code": "200",
"message": "操作成功",
"success": true
}
SQL 输出为：
select customer0_.id as id1_0_, customer0_.create_user_name as create_u2_0_, customer0_.created_date as created_3_0_, customer0_.del_flag as del_flag4_0_, customer0_.last_modified_date as last_mod5_0_, customer0_.last_modified_name as last_mod6_0_, customer0_.version as version7_0_, customer0_.address as address8_0_, customer0_.age as age9_0_, customer0_.name as name10_0_ from customer customer0_ where ( customer0_.del_flag=0) and (customer0_.name like ?) order by case when customer0_.name is null then 1 else 0 end, customer0_.name asc limit ?
一对多查询
使用 JPA 的好处就是可以使用 @OneToMany 等注解，以及懒加载查询优化注解 @EntityGraph。
1、修改实体类
public class Customer extends BaseDomain {
private static final long serialVersionUID = 1L;
@Schema(name = "")
@Column(name = "name")
private String name;
@Schema(name = "")
@Column(name = "age")
private Integer age;
@Schema(name = "")
@Column(name = "address")
private String address;
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "customer_id")
private List<SubUser> subUsers;
}
public class SubUser extends BaseDomain {
private static final long serialVersionUID = 1L;
@Schema(name = "")
@Column(name = "name")
private String name;
// @Schema(name = "")
// @Column(name = "customer_id")
// private String customerId;
@Schema(name = "")
@Column(name = "address")
private String address;
@ManyToOne
@JoinColumn
private Customer customer;
}
2、更改 CustomerRepository，这点格外重要，只有如此，才能使得 SpecificationBuilder 更有意义，否则即使可以连表查询，也会出现 N+1 问题。
@Repository
public interface CustomerRepository extends JpaRepository<Customer, Long>,
JpaSpecificationExecutor<Customer> {
@Override
@EntityGraph(
attributePaths = {"subUsers"}
)
List<Customer> findAll(Specification<Customer> spec);
@Override
@EntityGraph(
attributePaths = {"subUsers"}
)
Page<Customer> findAll(Specification<Customer> spec, Pageable pageable);
@Override
@EntityGraph(
attributePaths = {"subUsers"}
)
List<Customer> findAll(Specification<Customer> spec, Sort sort);
}
3、Service 层修改查询方法
public List<CustomerVO> queryList(CustomerDTO dto) {
List<Customer> customers = SpecificationBuilder.create(CustomerRepository.class)
.andLike(Customer::getName, dto.getName() + "%")
.select();
return customerStruct.modelToVO(customers);
}
4、查询结果为
{
"data": [
{
"name": "rookie",
"age": 26,
"address": "湖北武汉",
"subUserVOS": [
{
"name": "a1",
"address": "青藏高原"
},
{
"name": "a2",
"address": "青藏高原"
}
]
},
{
"name": "rookie1",
"age": 26,
"address": "湖北武汉",
"subUserVOS": [
{
"name": "c1",
"address": "黄土高原"
},
{
"name": "c2",
"address": "黄土高原"
}
]
},
{
"name": "rookie2",
"age": 26,
"address": "湖北武汉",
"subUserVOS": []
},
{
"name": "rookie3",
"age": 26,
"address": "湖北武汉",
"subUserVOS": []
}
],
"code": "200",
"message": "操作成功",
"success": true
}
5、SQL 输出
如果没有 CustomerRepository 的重写方法，则会出现 N+1 问题。
连表查询
除了上述查询方法的使用，我们还可以手动来增加 left join 的查询条件，比如说我们连表查询时，还要在 on 查询上增加额外的条件，也可以通过 SpecificationBuilder 来实现。
假设 Customer 和 SubUser 没有使用@JoinColumn 进行关联，而你此时想进行关联查询，可以这样做。
public List<CustomerVO> queryList(CustomerDTO dto) {
List<Customer> customers = SpecificationBuilder.create(CustomerRepository.class)
.andLike(Customer::getName, dto.getName() + "%")
.leftJoin(Customer::getSubUsers)// 表示 left join sub_user
.select();
return customerStruct.modelToVO(customers);
}
对应的 SQL 如下：
select
customer0_.id as id1_0_0_,
subusers1_.id as id1_1_1_,
customer0_.create_user_name as create_u2_0_0_,
customer0_.created_date as created_3_0_0_,
customer0_.del_flag as del_flag4_0_0_,
customer0_.last_modified_date as last_mod5_0_0_,
customer0_.last_modified_name as last_mod6_0_0_,
customer0_.version as version7_0_0_,
customer0_.address as address8_0_0_,
customer0_.age as age9_0_0_,
customer0_.name as name10_0_0_,
subusers1_.create_user_name as create_u2_1_1_,
subusers1_.created_date as created_3_1_1_,
subusers1_.del_flag as del_flag4_1_1_,
subusers1_.last_modified_date as last_mod5_1_1_,
subusers1_.last_modified_name as last_mod6_1_1_,
subusers1_.version as version7_1_1_,
subusers1_.address as address8_1_1_,
subusers1_.customer_id as custome10_1_1_,
subusers1_.name as name9_1_1_,
subusers1_.customer_id as custome10_1_0__,
subusers1_.id as id1_1_0__
from
customer customer0_
left outer join sub_user subusers1_ on
customer0_.id = subusers1_.customer_id
where
( customer0_.del_flag = 0)
and (customer0_.name like ?)
如果你想额外增加 on 查询条件，可以这样实现。
public List<CustomerVO> queryList(CustomerDTO dto) {
List<Customer> customers = SpecificationBuilder.create(CustomerRepository.class)
.andLike(Customer::getName, dto.getName() + "%")
// .leftJoin(Customer::getSubUsers)
.leftJoinAndOnEqualTo(Customer::getSubUsers,"name","a1")
.select();
return customerStruct.modelToVO(customers);
}
对应的 SQL 为
select
customer0_.id as id1_0_0_,
subusers1_.id as id1_1_1_,
customer0_.create_user_name as create_u2_0_0_,
customer0_.created_date as created_3_0_0_,
customer0_.del_flag as del_flag4_0_0_,
customer0_.last_modified_date as last_mod5_0_0_,
customer0_.last_modified_name as last_mod6_0_0_,
customer0_.version as version7_0_0_,
customer0_.address as address8_0_0_,
customer0_.age as age9_0_0_,
customer0_.name as name10_0_0_,
subusers1_.create_user_name as create_u2_1_1_,
subusers1_.created_date as created_3_1_1_,
subusers1_.del_flag as del_flag4_1_1_,
subusers1_.last_modified_date as last_mod5_1_1_,
subusers1_.last_modified_name as last_mod6_1_1_,
subusers1_.version as version7_1_1_,
subusers1_.address as address8_1_1_,
subusers1_.customer_id as custome10_1_1_,
subusers1_.name as name9_1_1_,
subusers1_.customer_id as custome10_1_0__,
subusers1_.id as id1_1_0__
from
customer customer0_
left outer join sub_user subusers1_ on
customer0_.id = subusers1_.customer_id
and (subusers1_.name =?)
where
( customer0_.del_flag = 0)
and (customer0_.name like ?)
关于 on 条件查询的实现，可以查看 SpecificationBuilder 中这段源码：
List<QueryParam> onQueryParams = queryParams.stream()
.filter(obj -> StringUtils.isNotEmpty(obj.getJoinName()))
.collect(Collectors.toList());
for (QueryParam onQueryParam : onQueryParams) {
List<QueryItem> queryItems = onQueryParam.getQueryItems();
if (CollectionUtils.isEmpty(queryItems)) {
root.join(onQueryParam.getJoinName(), onQueryParam.getJoinType());
} else {
Join<Object, Object> join = root
.join(onQueryParam.getJoinName(), onQueryParam.getJoinType());
for (QueryItem queryItem : queryItems) {
Object value = queryItem.getFieldValue();
switch (queryItem.getMatchCondition()) {
case EQUAL:
if (value instanceof String) {
// 关联表where查询
// andPredicates.add(criteriaBuilder
// .equal(join.get(queryItem.getFieldName()).as(String.class), value));
// 关联表on查询
join.on(criteriaBuilder
.equal(join.get(queryItem.getFieldName()).as(String.class), value));
} else if (value instanceof Integer) {
// andPredicates.add(criteriaBuilder
// .equal(join.get(queryItem.getFieldName()).as(Integer.class), value));
join.on(criteriaBuilder
.equal(join.get(queryItem.getFieldName()).as(Integer.class), value));
} else if (value instanceof Long) {
// andPredicates.add(criteriaBuilder
// .equal(join.get(queryItem.getFieldName()).as(Long.class), value));
// on查询
join.on(criteriaBuilder
.equal(join.get(queryItem.getFieldName()).as(Long.class), value));
}
break;
case LIKE:
if (value instanceof String) {
join.on(criteriaBuilder
.like(join.get(queryItem.getFieldName()).as(String.class),
"%" + value + "%"));
}
break;
default:
}
}
}
}
如果你感兴趣，可以取消注释代码，试一下将 subUser.name 查询放到 where 条件中。
if (value instanceof String) {
// 关联表where查询
andPredicates.add(criteriaBuilder
.equal(join.get(queryItem.getFieldName()).as(String.class), value));
// 关联表on查询
// join.on(criteriaBuilder
// .equal(join.get(queryItem.getFieldName()).as(String.class), value));
}
对应的 SQL 为：
select
customer0_.id as id1_0_0_,
subusers1_.id as id1_1_1_,
customer0_.create_user_name as create_u2_0_0_,
customer0_.created_date as created_3_0_0_,
customer0_.del_flag as del_flag4_0_0_,
customer0_.last_modified_date as last_mod5_0_0_,
customer0_.last_modified_name as last_mod6_0_0_,
customer0_.version as version7_0_0_,
customer0_.address as address8_0_0_,
customer0_.age as age9_0_0_,
customer0_.name as name10_0_0_,
subusers1_.create_user_name as create_u2_1_1_,
subusers1_.created_date as created_3_1_1_,
subusers1_.del_flag as del_flag4_1_1_,
subusers1_.last_modified_date as last_mod5_1_1_,
subusers1_.last_modified_name as last_mod6_1_1_,
subusers1_.version as version7_1_1_,
subusers1_.address as address8_1_1_,
subusers1_.customer_id as custome10_1_1_,
subusers1_.name as name9_1_1_,
subusers1_.customer_id as custome10_1_0__,
subusers1_.id as id1_1_0__
from
customer customer0_
left outer join sub_user subusers1_ on
customer0_.id = subusers1_.customer_id
where
( customer0_.del_flag = 0)
and (customer0_.name like ?)
and subusers1_.name =?
为什么要这样实现呢？首先我们要了解 on 和 where 的区别：
连接查询中，on是用来确定两张表的关联关系，关联好之后生成一个临时表，之后where对这个临时表再进行过滤筛选。
先执行on，后执行 where；on是建立关联关系在生成临时表时候执行，where是在临时表生成后对数据进行筛选的。
所以优先执行on条件查询，效率更高。
不仅如此，上述 SQL 执行结果为：
{
"data": [
{
"name": "rookie",
"age": 26,
"address": "湖北武汉",
"subUserVOS": [
{
"name": "a1",
"address": "青藏高原"
}
]
}
],
"code": "200",
"message": "操作成功",
"success": true
}
这明显不是我们想要的结果。
修改数据
在本项目中，表结构中都包含了 version 这个字段，即每次更新操作，version 都应该加1。
CustomerRepository文件
@Repository
public interface CustomerRepository extends JpaRepository<Customer, Long>,
JpaSpecificationExecutor<Customer> {
@Modifying
@Query(value = "update customer set age = :age where name = :name and del_flag=0", nativeQuery = true)
void updateByName(@Param("name") String name, @Param("age") int age);
Customer findByName(String name);
}
Service 修改方法
@Transactional
@Override
public CustomerVO edit(CustomerDTO dto) {
// 通过自定义修改方法的方式来达到修改数据，先修改再查询，version没有改变，修改时间也不变
// customerRepository.updateByName(dto.getName(), dto.getAge());
// return customerStruct.modelToVO(customerRepository.findByName(dto.getName()));
// 先查询，再修改,这种方式才会触发乐观锁，即where条件中有version条件，更新操作verison+1，修改时间也会变化
Customer customer = customerRepository.findByName(dto.getName());
customer.setAge(dto.getAge());
customerRepository.save(customer);
return customerStruct.modelToVO(customer);
}
Swagger
启动项目后，访问 swagger，页面展示如下：
总结
上文中本人对于实现的 SpecificationBuilder 类还算满意，一开始只是为了实现分页查询，慢慢想实现 Mybatis Plus 的那种链式查询，以及最后想要实现连接查询。代码实现目前就这样吧，如果大家有什么好玩的想法，欢迎大家留言评论。
感兴趣的朋友可以去我的 Github 下载相关代码，如果对你有所帮助，不妨 Star 一下，谢谢大家支持！
参考文献
Spring Data JPA中多表联合查询最佳实践
spring data jpa 动态查询（工具类封装）
springboot jpa 分页查询工具类
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