mybatis-plus LambdaQueryWrapper之判断值是否存在，存在则加入查询，反之亦然

需求如下:
如果：如果设置值的时候，值为空则不执行查询语句

代码：
当isDeleted为null的时候

@Test    void method() {        Integer isDeleted = null;        LambdaQueryWrapper queryWrapper = new LambdaQueryWrapper<>();        queryWrapper.eq(!ObjectUtils.isEmpty(isDeleted),DeviceBrand::getIsDeleted,isDeleted);        log.info(String.valueOf(queryWrapper));    }

调试结果：

此时expression里面的nORMal size == 0

当isDeleted为1的时候

@Test    void method() {        Integer isDeleted = 1;        LambdaQueryWrapper queryWrapper = new LambdaQueryWrapper<>();        queryWrapper.eq(!ObjectUtils.isEmpty(isDeleted),DeviceBrand::getIsDeleted,isDeleted);        log.info(String.valueOf(queryWrapper));    }

此时expression里面的normal size == 3

于是乎我翻了一下mybatis-plus源码

 protected Children addCondition(boolean condition, R column, SqlKeyword sqlKeyword, Object val) {        return maybeDo(condition, () -> appendSqlSegments(columnToSqlSegment(column), sqlKeyword,            () -> formatParam(null, val)));    }    protected final Children maybeDo(boolean condition, DoSomething something) {        if (condition) {            something.doIt();        }        return typedThis;    }

如果condition为 true则执行右边的函数，为false则反之

来源地址：https://blog.csdn.net/qq_43375661/article/details/126877725