MyBatis-Plus中如何使用ResultMap的方法示例

目录

• 问题说明
• 解决方法
• 自定义@AutoResultMap注解

create table tb_book
(
    id     bigint primary key,
    name   varchar(32),
    author varchar(20)
);
create table tb_hero
(
    id      bigint primary key,
    name    varchar(32),
    age     int,
    skill   varchar(32),
    bid bigint
);

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import com.fasterxml.jackson.annotation.JsonInclude;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
@Getter
@Setter
@NoArgsConstructor
@TableName("tb_hero")
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Hero {
    @TableId("id")
    private Long id;
    @TableField(value = "name", keepGlobalFormat = true)
    private String name;
    @TableField(value = "age", keepGlobalFormat = true)
    private Integer age;
    @TableField(value = "skill", keepGlobalFormat = true)
    private String skill;
    @TableField(value = "bid", keepGlobalFormat = true)
    private Long bookId;
    // *********************************
    // 数据库表中不存在以下字段(表join时会用到)
    // *********************************
    @TableField(value = "book_name", exist = false)
    private String bookName;
    @TableField(value = "author", exist = false)
    private String author;
}

@Mapper
@Repository
public interface HeroMapper extends BaseMapper<Hero> {
    @Select({"SELECT tb_hero.*, tb_book.name as book_name, tb_book.author" +
            " FROM tb_hero" +
            " LEFT JOIN tb_book" +
            " ON tb_hero.bid = tb_book.id" +
            " ${ew.customSqlSegment}"})
    IPage<Hero> pageQueryHero(@Param(Constants.WRAPPER) Wrapper<Hero> queryWrapper,
                              Page<Hero> page);
}

@TableName(value = "tb_hero", autoResultMap = true)
public class Hero {
}

import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.ResultMap;
import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Repository;
@Mapper
@Repository
public interface HeroMapper extends BaseMapper<Hero> {
    @ResultMap("mybatis-plus_Hero")
    @Select({"SELECT tb_hero.*, tb_book.name as book_name, tb_book.author" +
            " FROM tb_hero" +
            " LEFT JOIN tb_book" +
            " ON tb_hero.bid = tb_book.id" +
            " ${ew.customSqlSegment}"})
    IPage<Hero> pageQueryHero(@Param(Constants.WRAPPER) Wrapper<Hero> queryWrapper,
                              Page<Hero> page);
}

/**
 * 自动构建 resultMap 并注入(如果条件符合的话)
 */
void initResultMapIfNeed() {
    if (autoInitResultMap && null == resultMap) {
        String id = currentNamespace + DOT + MYBATIS_PLUS + UNDERSCORE + entityType.getSimpleName();
        List<ResultMapping> resultMappings = new ArrayList<>();
        if (havePK()) {
            ResultMapping idMapping = new ResultMapping.Builder(configuration, keyProperty, StringUtils.getTargetColumn(keyColumn), keyType)
                .flags(Collections.singletonList(ResultFlag.ID)).build();
            resultMappings.add(idMapping);
        }
        if (CollectionUtils.isNotEmpty(fieldList)) {
            fieldList.forEach(i -> resultMappings.add(i.getResultMapping(configuration)));
        }
        ResultMap resultMap = new ResultMap.Builder(configuration, id, entityType, resultMappings).build();
        configuration.addResultMap(resultMap);
        this.resultMap = id;
    }
}

import java.lang.annotation.*;
/**
 * 使用@AutoResultMap注解的实体类
 * 自动生成{auto.mybatis-plus_类名}为id的resultMap
 * {@link MybatisPlusConfig#initAutoResultMap()}
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface AutoResultMap {
}

package com.bytesfly.mybatis.config;
import cn.hutool.core.util.ClassUtil;
import cn.hutool.core.util.ReflectUtil;
import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.core.metadata.TableInfo;
import com.baomidou.mybatisplus.core.metadata.TableInfoHelper;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import com.baomidou.mybatisplus.extension.toolkit.JdbcUtils;
import com.bytesfly.mybatis.annotation.AutoResultMap;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.builder.MapperBuilderAssistant;
import org.mybatis.spring.SqlSessionTemplate;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.annotation.EnableTransactionManagement;
import javax.annotation.PostConstruct;
import java.util.Set;
/**
 * 可添加一些插件
 */
@Configuration
@EnableTransactionManagement(proxyTargetClass = true)
@MapperScan(basePackages = "com.bytesfly.mybatis.mapper")
@Slf4j
public class MybatisPlusConfig {
    @Autowired
    private SqlSessionTemplate sqlSessionTemplate;
    /**
     * 分页插件(根据jdbcUrl识别出数据库类型, 自动选择适合该方言的分页插件)
     * 相关使用说明: https://baomidou.com/guide/page.html
     */
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(DataSourceProperties dataSourceProperties) {
        String jdbcUrl = dataSourceProperties.getUrl();
        DbType dbType = JdbcUtils.getDbType(jdbcUrl);
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(dbType));
        return interceptor;
    }
    /**
     * @AutoResultMap注解的实体类自动构建resultMap并注入
     */
    @PostConstruct
    public void initAutoResultMap() {
        try {
            log.info("--- start register @AutoResultMap ---");
            String namespace = "auto";
            String packageName = "com.bytesfly.mybatis.model.db.resultmap";
            Set<Class<?>> classes = ClassUtil.scanPackageByAnnotation(packageName, AutoResultMap.class);
            org.apache.ibatis.session.Configuration configuration = sqlSessionTemplate.getConfiguration();
            for (Class clazz : classes) {
                MapperBuilderAssistant assistant = new MapperBuilderAssistant(configuration, "");
                assistant.setCurrentNamespace(namespace);
                TableInfo tableInfo = TableInfoHelper.initTableInfo(assistant, clazz);
                if (!tableInfo.isAutoInitResultMap()) {
                    // 设置 tableInfo的autoInitResultMap属性 为 true
                    ReflectUtil.setFieldValue(tableInfo, "autoInitResultMap", true);
                    // 调用 tableInfo#initResultMapIfNeed() 方法，自动构建 resultMap 并注入
                    ReflectUtil.invoke(tableInfo, "initResultMapIfNeed");
                }
            }
            log.info("--- finish register @AutoResultMap ---");
        } catch (Throwable e) {
            log.error("initAutoResultMap error", e);
            System.exit(1);
        }
    }
}

@Mapper
@Repository
public interface BookMapper extends BaseMapper<Book> {
    @ResultMap("auto.mybatis-plus_BookAgg")
    @Select({"SELECT tb_book.id, max(tb_book.name) as name, array_agg(distinct tb_hero.id order by tb_hero.id asc) as hero_ids" +
            " FROM tb_hero" +
            " INNER JOIN tb_book" +
            " ON tb_hero.bid = tb_book.id" +
            " GROUP BY tb_book.id"})
    List<BookAgg> agg();
}

@Getter
@Setter
@NoArgsConstructor
@AutoResultMap
public class BookAgg {
    @TableId("id")
    private Long bookId;
    @TableField("name")
    private String bookName;
    @TableField("hero_ids")
    private Object heroIds;
}