Mybatis-plus在原有的select查询语句中动态追加查询条件

一、适用场景

1、使用了xml形式的mapper。
2、不想在select查询中大量使用<if>标签来判断条件是否存在而加入条件。

二、步骤

1、自定义wrapper继承QueryWrapper：

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import org.apache.shiro.util.StringUtils;

public class CustomWrapper<T> extends QueryWrapper<T> {

    /**
     * ifSql记录自定义追加的条件
     */
    private String ifSql;

    /**
     * 赋值给ifSql
     * @return
     */
    public CustomWrapper init(){
        String sqlSegment = getSqlSegment();
        if (StringUtils.hasText(sqlSegment)){
            this.ifSql = "and" + getSqlSegment();
        }
        return this;
    }

    public String getIfSql() {
        return this.ifSql;
    }

   //自定义eq、like等等方法，动态判断是否要加入条件

    public CustomWrapper eq(String column,String val){
        this.eq(StringUtils.hasText(val),column,val);
        return this;
    }

    public CustomWrapper like(String column,String val){
        this.like(StringUtils.hasText(val),column,val);
        return this;
    }
　　
    public CustomWrapper ge(String column,String val){
        this.ge(StringUtils.hasText(val),column,val);
        return this;
    }

    public CustomWrapper le(String column,String val){
        this.le(StringUtils.hasText(val),column,val);
        return this;
    }
}

2、在mapper.java接口中定义方法：

@Mapper
public interface IApplyInfoMapper extends CustomizedBaseMapper<ApplyInfo> {

    List<ApplyInfo> getApplyList(@Param(Constants.WRAPPER) Wrapper ew);

    //...

}

3、在xml中加入标识符 ${ew.ifSql}

<select id="getAllApplyInfoList" resultMap="allApplyInfoMapper">
        SELECT
            ...
        FROM b
        LEFT JOIN w ON b.wid=  w.id
        LEFT JOIN n ON b.nid= n.id
        WHERE b.ZT = '1'
        ${ew.ifSql}
</select>

4、在service层加入mybatis-plus自定义wrapper条件

@Service
public class ApplyInfoServiceImpl extends ServiceImpl<IApplyInfoMapper,ApplyInfo> implements IApplyInfoService {

    @Autowired
    private IApplyInfoMapper mapper;

    @Override
    public PageInfo queryPage(PageInfo pageInfo) {
        Page page = PageUtils.getPage(pageInfo);
        CustomWrapper<ApplyInfo> wrapper = getCustomWrapper(pageInfo);
        List<ApplyInfo> list = mapper.getApplyList(wrapper.init());
        PageUtils.setPageInfoProperty(pageInfo,page,list);
        return pageInfo;
    }

    /**
     * 这里的我将pageInfo为传入的条件
     * @return
     */
    private CustomWrapper<ApplyInfo> getCustomWrapper(PageInfo pageInfo) {
        CustomWrapper<ApplyInfo> wrapper = new CustomWrapper<>();
        wrapper.eq("b.id",pageInfo.getProperty1())
        return wrapper;
    }

    ......

}

5、最终执行sql语句为:

SELECT
...
FROM b
LEFT JOIN w ON b.wid=  w.id
LEFT JOIN n ON b.nid= n.id
WHERE b.ZT = '1'
AND b.id="这里为你在service中传入的值"