下面的语句就可以匹配:db.things.find( { a : { $size: 1 } } ); 官网上说不能用来匹配一个范围内的元素,如果想找$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...
deptData);WriteResult({"nMatched":1,"nUpserted":0,"nModified":1})db.dept.find();"_id":ObjectId("5d0492d3db2a129b32288894"),"deptno":50,"dname":"乞讨部","loc":"家里蹲","count":60,"avg":9000}"_id":
>db.mediaCollection.insert({"Type":"DVD",Title:"Toy Story 3",Released:2010}) 2. $gt (greater than) 1 2 3 4 5 6 7 8 9 >db.mediaCollection.find({Released:{$gt:2000}},{"Cast":0}).toArray() [ { "_id":ObjectId("53548254d85b463e729a2e59"), "Type":"DVD", "Title":"To...
path: <Array Field Path>, includeArrayIndex: <string>, preserveNullAndEmptyArrays: <boolean> } } 例子 以下示例将为每个对象的type和color组合使用$unwind阶段。该聚合管道包含以下步骤: 将$group阶段与$addToSet结合使用,从而为每个type创建新文档,同时附带新字段colors,而该字段包含集合中出现的该花卉类型的所...
大于等于($gte):Greater than equals db.qtfm__audio_info.find({playLength:{$gte:2}}) 不等于($ne):Not equals db.qtfm__audio_info.find({name:{$ne:'11'}}) 小于等于($lte):Less than equals db.getCollection("qtfm__audio_info").find({playLength:{$lte:22},code:"TT0000066_0001",'al...
当您只需要所选文档中的一个特定数组元素时,可以在find()方法或findOne()方法的投影文档中使用$。 运算符的语法$如下所示: db.collection.find( { <array>: <condition> ... }, { "<array>.$": 1 } ) db.collection.find( { <array.field>: <condition> ...}, { "<array>.$": 1 } ) ...
db.stu.find({name:"Jerry",age:18})[0] 1. findOne()返回的就是一个文档,相当于find(<条件>)[0] findOne()可以直接在最后指定某一条属性,例如findOne(<条件>).name find(<条件>).count() , find(<条件>).length() 可以得到满足条件文档的数量 ...
grades: [60, 70, 40] # sum of this array = 170 (take this) }, { name: 'Doe', grades: [30, 20, 10] # sum of this array = 60 (don't take this) } 我对该系列进行了如下投影: db.collections.find({}, { { sumOfGrades: { $sum: "$grades" } ...
3. $gte(greater than or equal to) > db.mediaCollection.find( { Released : {$gte : 1999 } }, { "Cast" : 0 } ).toArray() [ { "_id" : ObjectId("53548225d85b463e729a2e57"), "Type" : "DVD", "Title" : "Matrix, The", "Released" : 1999 }, { "_id" : ObjectId("5354...
db.inventory.find( {}, {"instock": {$slice:1},"instock.warehouse":0} ) In previous versions, the projection applies both projections and returns the first element ($slice: 1) in theinstockarray but suppresses thewarehousefield in the projected element. Starting in MongoDB 4.4, to achiev...