simple-query 让简单的查询更简单 · Pull Request !194 · baomidou/mybatis-plus

### 该Pull Request关联的Issue

### 修改描述

封装了下业务中常用的查表方法

### 测试用例

```java
package com.baomidou.mybatisplus.test.toolkit;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.baomidou.mybatisplus.core.toolkit.Assert;
import com.baomidou.mybatisplus.core.toolkit.Wrappers;
import com.baomidou.mybatisplus.extension.toolkit.SimpleQuery;
import com.baomidou.mybatisplus.extension.toolkit.SqlHelper;
import com.baomidou.mybatisplus.test.BaseDbTest;
import com.baomidou.mybatisplus.test.rewrite.Entity;
import com.baomidou.mybatisplus.test.rewrite.EntityMapper;
import org.junit.jupiter.api.Test;

import java.util.*;

/**
 * 简单查询工具类测试
 *
 * @author <achao1441470436@gmail.com>
 * @since 2021/11/9 18:30
 */
public class SimpleQueryTest extends BaseDbTest<EntityMapper> {

@Test
    public void testList() {
        // 我要这张表里的ids
        List<Long> entityIds = SimpleQuery.list(Wrappers.lambdaQuery(), Entity::getId);

Assert.isTrue(entityIds.equals(Arrays.asList(1L, 2L)), "Ops!");
        // 可叠加后续操作
        List<String> names = SimpleQuery.list(Wrappers.lambdaQuery(), Entity::getName, e -> Optional.ofNullable(e.getName()).map(String::toUpperCase).ifPresent(e::setName));

Assert.isTrue(names.equals(Arrays.asList("RUBEN", "A CHAO")), "Ops!");
    }

@Test
    public void testMap() {
        // 我要这个表里对应条件的用户，用id作为key给我一个map
        Map<Long, Entity> idEntityMap = SimpleQuery.keyMap(Wrappers.<Entity>lambdaQuery().eq(Entity::getId, 1L), Entity::getId);
        // 校验结果
        Entity entity = new Entity();
        entity.setId(1L);
        entity.setName("ruben");
        Assert.isTrue(idEntityMap.equals(Collections.singletonMap(1L, entity)), "Ops!");

// 如果我只想要id和name组成的map
        Map<Long, String> idNameMap = SimpleQuery.map(Wrappers.lambdaQuery(), Entity::getId, Entity::getName);
        // 校验结果
        Map<Long, String> map = new HashMap<>(1 << 2);
        map.put(1L, "ruben");
        map.put(2L, "a chao");
        Assert.isTrue(idNameMap.equals(map), "Ops!");

// 同样支持叠加后续操作
//        SimpleQuery.keyMap(Wrappers.lambdaQuery(), Entity::getId, System.out::println, System.out::println);

}

@Test
    public void testGroup() {
        // 我需要相同名字的用户的分为一组，再造一条数据
        BaseMapper<Entity> mapper = SqlHelper.getMapper(Entity.class);
        Entity entity = new Entity();
        entity.setId(3L);
        entity.setName("ruben");
        mapper.insert(entity);

// 简单查询
        Map<String, List<Entity>> nameUsersMap = SimpleQuery.group(Wrappers.lambdaQuery(), Entity::getName);

// 校验结果
        Map<String, List<Entity>> map = new HashMap<>(1 << 2);
        Entity chao = new Entity();
        chao.setId(2L);
        chao.setName("a chao");
        map.put("a chao", Collections.singletonList(chao));

Entity ruben = new Entity();
        ruben.setId(1L);
        ruben.setName("ruben");
        Entity ruben2 = new Entity();
        ruben2.setId(3L);
        ruben2.setName("ruben");
        map.put("ruben", Arrays.asList(ruben, ruben2));
        Assert.isTrue(nameUsersMap.equals(map), "Ops!");

}

@Override
    protected String tableDataSql() {
        return "insert into entity(id,name) values(1,'ruben'),(2,'a chao');";
    }

@Override
    protected List<String> tableSql() {
        return Arrays.asList("drop table if exists entity", "CREATE TABLE IF NOT EXISTS entity (" +
            "id BIGINT NOT NULL," +
            "name VARCHAR(30) NULL DEFAULT NULL," +
            "PRIMARY KEY (id))");
    }

}

```

### 修复效果的截屏

GVPbaomidou/mybatis-plus

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