Learn how to query for null or missing fields in MongoDB using various methods including the MongoDB Atlas UI and MongoDB Compass. Understand different query operators' treatment of null values.
{"_id":900,"name":null} 存在性筛查¶ The{name:{$exists:false}}query matches documents that do not contain theitemfield: db.users.find({name:{$exists:false}}) 该查询只返回那些没有包含条目字段的文档: {"_id":901} 参见 The reference documentation for the$typeand$existsoperators. ...
uassert(6887104, "failed to create new JS object", newPlainObject); JS::RootedObject emptyObj{cx, newPlainObject}; JS::RootedValue emptyObjVal(cx); emptyObjVal.setObjectOrNull(emptyObj); JS::RootedValue nullVal(cx); nullVal.setNull(); if (args.length() > 4 && args.get(4).isObjec...
# 使用includeArrayIndex选项来输出数组元素的数组索引db.books2.aggregate([{$match:{"author.name":"ll"}},{$unwind:{path:"$tag", includeArrayIndex: "arrayIndex"}}]) 发现:只输出tag不为null的数据,并且多了个数组加下标的字段 # 使用preserveNullAndEmptyArrays选项在输出中包含缺少size字段,null或空数...
The{ name : null }query matches documents that either contain thenamefield whose value isnullorthat do not contain thenamefield. Given the following query: db.users.find( { name: null } ) The query returns both documents: { "_id" : 900, "name" : null } ...
preserveNullAndEmptyArrays: <boolean> } } 如果为输入文档中不存在的字段指定路径,或者该字段为空数组,则$unwind默认会忽略输入文档,并且不会输出该输入文档的文档。 版本3.2中的新功能:要输出数组字段丢失的文档,null或空数组,请使用选项preserveNullAndEmptyArrays。
增加icludeArrayIndex,preserveNullAndEmptyArrays两个可选配置 { $unwind: { path:<field path>, includeArrayIndex:<string>, preserveNullAndEmptyArrays:<boolean>} } 示例:# 假设articles文档集合是这样: { title:'this is article A', author:'John', _id:1, comments: ['a','b','c']} ...
(null);mongoTemplate.insert(dog);returnnull;}@OverridepublicDogupdate(Dog dog){Query query=newQuery(Criteria.where("id").is(dog.getId()));Update update=newUpdate().set("name",dog.getName()).set("age",dog.getAge());//更新查询出的结果的第一条mongoTemplate.updateFirst(query,update,Dog....
mongoCollection.updateOne(queryFilter, updateDocument, updateOptions).getAsync(task -> { if (task.isSuccess()) { if(task.get().getUpsertedId() != null) { Log.v("EXAMPLE", "successfully upserted a document with id " + task.get().getUpsertedId()); } else { Log.v("EXAMPLE", "suc...
null > db.test.insert({'_id': 'cswuyg', 'super_admin': true}) > db.test.findOne({'_id': 'cswuyg'}) { "_id" : "cswuyg", "super_admin" : true } db.test.update({'_id': 'cswuyg'}, {$set: {'super_admin': true}}) ...