false如果为path,如果 为 null、缺失或空大量,则$unwind不会输出文档。 默认值为false。 行为 非数组字段路径 如果操作数没有解析为数组,但没有缺失、为null或空数组,$unwind会将该操作数视为单元素数组。 当操作数为null、缺失或空数组时,$unwind遵循为preserveNullAndEmptyArrays选项设置的行为。
* Aggregates/Bson 实现$unwind*/@TestpublicvoidtestUnwindAggregates(){ String CLOTHING_COLLECTION= "clothing";//调用Aggregates的unwind聚合操作符 注意,Aggregates这里需要传入$Bson unwindBson = Aggregates.unwind("$sizes");//建一个List<Bson> 把unwindBson传进去List<Bson> bsonList =newArrayList<>();...
$unwind stage : splits each movie document into multiple documents, one for each cast member in the original document. For each original document, this stage unwinds the Cast array of cast members and creates separate, unique documents with the same values as the original document, except for...
第一个给出了一个错误,因为我将字段名留空(我不知道该放什么)。 第二个返回一个合并的数组,但包含重复的数组。 ✅ 最佳回答: 当您想要对所有文档进行分组时,需要添加{_id: null} 这意味着将所有文件分组。 也许你需要这个 db.collection.aggregate([ { "$unwind": "$configs" }, { $group: { _id:...
{ "_id" : "objectives/core/1004" } 然而,这在旧版本的MongoDB中不起作用,因为它们不支持preserveNullAndEmptyArrays属性-它们的 * 常规 * unwind操作(没有该属性)不会从上面的清单中生成文档编号4。你有什么想法如何使用Mongo3.0实现这个功能吗? mongodb ...
$unwind: "$result.events" }, { $unwind: "$result.events.amount" }, { $addFields: { amount_sum: { $sum: { $toInt: { $last: "$result.events.amount" } } } } }, { $group: { _id: { id: "$_id" }, sum_amount: { ...
$unwind− This is used to unwind document that are using arrays. When using an array, the data is kind of pre-joined and this operation will be undone with this to have individual documents again. Thus with this stage we will increase the amount of documents for the next stage. ...
+ Arrays.toString(location) + "]"; } } 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 若要查找 中的位置,可以使用以下查询:Circle ...
Database Commands / Aggregation Definition aggregate Performs aggregation operation using theaggregation pipeline. The pipeline allows users to process data from a collection or other source with a sequence of stage-based manipulations. Tip Inmongosh, this command can also be run through thedb.aggregat...
You can insert multiple documents into a collection by passing an array toinsertMany(). The following code creates additional person documents and a new company collection: db.person.insertMany([{name:'Brian', company:'Beta Inc'},{name:'Claire', ...