MyBatis-Plus Mapper CRUD 接口之Select

方法

// 根据 ID 查询
T selectById(Serializable id);
// 根据 entity 条件，查询一条记录
T selectOne(@Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

// 查询（根据ID 批量查询）
List<T> selectBatchIds(@Param(Constants.COLLECTION) Collection<? extends Serializable> idList);
// 根据 entity 条件，查询全部记录
List<T> selectList(@Param(Constants.WRAPPER) Wrapper<T> queryWrapper);
// 查询（根据 columnMap 条件）
List<T> selectByMap(@Param(Constants.COLUMN_MAP) Map<String, Object> columnMap);
// 根据 Wrapper 条件，查询全部记录
List<Map<String, Object>> selectMaps(@Param(Constants.WRAPPER) Wrapper<T> queryWrapper);
// 根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值
List<Object> selectObjs(@Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

// 根据 entity 条件，查询全部记录（并翻页）
IPage<T> selectPage(IPage<T> page, @Param(Constants.WRAPPER) Wrapper<T> queryWrapper);
// 根据 Wrapper 条件，查询全部记录（并翻页）
IPage<Map<String, Object>> selectMapsPage(IPage<T> page, @Param(Constants.WRAPPER) Wrapper<T> queryWrapper);
// 根据 Wrapper 条件，查询总记录数
Integer selectCount(@Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

测试代码

selectById

@Test
void selectById() {
	BlogType blogType = blogTypeMapper.selectById(1);
	System.out.println(blogType.getId() + "," + blogType.getName() + "," + blogType.getSortNum());
}

selectOne

如果查到的数据不是1条时会报错

@Test
void selectOne() {
	QueryWrapper<BlogType> blogTypeQueryWrapper = new QueryWrapper<>();
	blogTypeQueryWrapper.eq("name", "MyBatis");
	BlogType blogType = blogTypeMapper.selectOne(blogTypeQueryWrapper);
	System.out.println(blogType.getId() + "," + blogType.getName() + "," + blogType.getSortNum());
}

selectBatchIds

@Test
void selectBatchIds() {
	List<Integer> idList = new ArrayList<>();
	idList.add(1);
	idList.add(5);
	idList.add(6);
	idList.add(7);
	List<BlogType> blogTypeList = blogTypeMapper.selectBatchIds(idList);
	for (BlogType blogType : blogTypeList) {
		System.out.println(blogType.getId() + "," + blogType.getName() + "," + blogType.getSortNum());
	}
}

selectList

@Test
void selectList() {
	//参数为空时查询所有
	List<BlogType> blogTypeList = blogTypeMapper.selectList(null);
	for (BlogType blogType : blogTypeList) {
		System.out.println(blogType.getId() + "," + blogType.getName() + "," + blogType.getSortNum());
	}
	System.out.println("------------------------");
	//根据条件查询
	QueryWrapper<BlogType> blogTypeQueryWrapper = new QueryWrapper<>();
	blogTypeQueryWrapper.like("name", "a");
	List<BlogType> blogTypeList1 = blogTypeMapper.selectList(blogTypeQueryWrapper);
	for (BlogType blogType : blogTypeList1) {
		System.out.println(blogType.getId() + "," + blogType.getName() + "," + blogType.getSortNum());
	}
}

selectByMap

@Test
void selectByMap() {
	Map<String, Object> map = new HashMap<>(16);
	map.put("sortNum", 81);
	List<BlogType> blogTypeList = blogTypeMapper.selectByMap(map);
	for (BlogType blogType : blogTypeList) {
		System.out.println(blogType.getId() + "," + blogType.getName() + "," + blogType.getSortNum());
	}
}

selectMaps

查询到的数据以键值对的方式存储在map中

@Test
void selectMaps() {
	QueryWrapper<BlogType> blogTypeQueryWrapper = new QueryWrapper<>();
	blogTypeQueryWrapper.gt("id", 5).like("name", "a");
	List<Map<String, Object>> mapList = blogTypeMapper.selectMaps(blogTypeQueryWrapper);
	for (Map<String, Object> map : mapList) {
		System.out.println(map.get("id")+","+map.get("name")+","+map.get("sortNum"));
	}
}

selectObjs

只返回一个字段

@Test
void selectObjs() {
	QueryWrapper<BlogType> blogTypeQueryWrapper = new QueryWrapper<>();
	//选择要查询的字段,不选择就返回第一个字段(一般是id)
	blogTypeQueryWrapper.select("name");
	//查询条件
	blogTypeQueryWrapper.gt("id", 5);
	List<Object> objectList = blogTypeMapper.selectObjs(blogTypeQueryWrapper);
	System.out.println(objectList);
}

selectPage

先配置分页插件

package com.ledao;

import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import com.baomidou.mybatisplus.extension.plugins.pagination.optimize.JsqlParserCountOptimize;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.annotation.EnableTransactionManagement;

/**
 * @author LeDao
 * @company
 * @create 2021-07-23 14:15
 */
@EnableTransactionManagement
@Configuration
public class MybatisPlusConfig {

    @Bean
    public PaginationInterceptor paginationInterceptor() {
        PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
        // 设置请求的页面大于最大页后操作， true调回到首页，false 继续请求  默认false
        // paginationInterceptor.setOverflow(false);
        // 设置最大单页限制数量，默认 500 条，-1 不受限制
        // paginationInterceptor.setLimit(500);
        // 开启 count 的 join 优化,只针对部分 left join
        paginationInterceptor.setCountSqlParser(new JsqlParserCountOptimize(true));
        return paginationInterceptor;
    }
}

测试

@Test
void selectPage() {
	//设置查询条件
	QueryWrapper<BlogType> blogTypeQueryWrapper = new QueryWrapper<>();
	blogTypeQueryWrapper.gt("id", 7);
	//设置当前页以及每页记录数
	Page<BlogType> page = new Page<>(2, 2);
	//获取记录
	Page<BlogType> blogTypePage = blogTypeMapper.selectPage(page, blogTypeQueryWrapper);
	List<BlogType> blogTypeList = blogTypePage.getRecords();
	for (BlogType blogType : blogTypeList) {
		System.out.println(blogType);
	}
}

selectMapsPage

@Test
void selectMapsPage() {
	//设置查询条件
	QueryWrapper<BlogType> blogTypeQueryWrapper = new QueryWrapper<>();
	blogTypeQueryWrapper.gt("id", 7);
	//设置当前页以及每页记录数
	Page page = new Page<>(2, 2);
	IPage<Map<String, Object>> mapIPage = blogTypeMapper.selectMapsPage(page, blogTypeQueryWrapper);
	for (Map<String, Object> record : mapIPage.getRecords()) {
		System.out.println(record);
	}
}

selectCount

@Test
void selectCount() {
	QueryWrapper<BlogType> blogTypeQueryWrapper = new QueryWrapper<>();
	blogTypeQueryWrapper.gt("id", 7);
	int count = blogTypeMapper.selectCount(blogTypeQueryWrapper);
	System.out.println(count);
}