Matches numeric or binary values in which any bit from a set of bit positions has a value of 1. Projection Operators Name Description $ Projects the first element in an array that matches the query condition. $elemMatch Projects the first element in an array that matches the specified $elem...
官网上说不能用来匹配一个范围内的元素,如果想找$size<5之类的,他们建议创建一个字段来保存元素的数量。 You cannot use $size to find a range of sizes (for example: arrays with more than 1 element). If you need to query for a range, create an extra size field that you increment when you ...
$first Returns the first element in an array. $function Defines a custom aggregation expression. $last Returns the last element in an array. $isNumber Returns boolean true if the specified expression resolves to an integer, decimal, double, or long.Returns boolean false if the expression resolves...
You cannot use $size to find a range of sizes (for example: arrays with more than 1 element). If you need to query for a range, create an extra size field that you increment when you add elements. 7)$exists $exists用来判断一个元素是否存在: 如: db.things.find( { a : { $exists ...
{$arrayElemAt:[<arrayexpression>, 0 ] } Behavior Valid Operands Valid operand for$firstmust resolve to an array, null, or missing If the operand resolves to a non-empty array,$firstreturns the first element in the array: If the operand resolves to an empty array[],$firstdoes not return...
Query query = new Query(); query.addCriteria(Criteria.where("mapData.scheduleId").in(ids)); if(status == -3){//不等于-3的时候按照状态获取 log.info("no status ",status); }else{ //等于-3的时候获取全部 query.addCriteria(Criteria.where("mapData.status").in(status)); } int totalSu...
In previous versions, MongoDB returns the first element (instock.$) in theinstockarray that matches the query condition; i.e. the positional projection"instock.$"takes precedence and the$slice:1is a no-op. The"instock.$": { $slice: 1 }does not exclude any other document field. ...
如果要向数组中增加或删除一个元素,set和set和inc 都不能很好的满足这种需求,MongoDB有专用的 Array Operator,用于修改数组字段。 1,使用$push向doc中增加数组,或插入新的元素 $push:如果doc中存在相应的数组字段,那么向数组的尾部插入一个元素;如果doc中不存在相应的数组字段,那么向doc中创建一个数组字段,并初始...
需与$each一起使用。 $sort:推入元素后,排序。$sort: {ELEMENT_KEY: 1|-1}。ELEMENT_KEY为数组元素的键,1为升序,-1为降序。需与$each一起使用。上述KEY等键可以使用a.b的形式指定内嵌文档(可为数组)的字段;可以使用a.INDEX的形式通过下标指定数组元素;若QUERY_DOC使用a.b进行查询,则可以通过定位操作符$...
$: Acts as a placeholder to update the first element that matches the query condition in an update. 示例1,使用empty filter作为query filter db.users.updateMany( {}, {$inc:{"comments.$.unlikes":1}} ) 1. 2. 3. 4. MongoDB抛出错误消息: ...