aggregation-framework

来源： https://stackoverflow.com/questions/34377286/mongodb-aggregation-project-field-values-as-fields

来源： https://stackoverflow.com/questions/40654446/remove-duplicate-documents-based-on-field

来源： https://stackoverflow.com/questions/62559332/mongodb-aggregation-vs-mongoose-virtuals

来源： https://stackoverflow.com/questions/63374525/avoid-having-null-fields-in-result-when-using-datefromstring-on-a-field

来源： https://stackoverflow.com/questions/63378828/mongoose-query-to-sort-main-document-subdocument-by-particular-field

来源： https://stackoverflow.com/questions/62915707/mongodb-aggregation-how-to-check-if-an-object-containing-multiple-properties-ex

来源： https://stackoverflow.com/questions/45412506/compare-embedded-document-to-parent-field-with-mongodb

问题 How can i reverse populate in mongo. I have 2 schema's User: var user_scheme = new mongoose.Schema({ name:String, age:Number, roles:{ type:mongoose.Schema.Types.ObjectId, ref:'Role' } }); Role: var role_scheme = new mongoose.Schema({ name:String, }); Documents: ///user { "_id" : ObjectId("5bf9a19b01ce3e19b440aed8"), "name" : "user1", "age" : 22, "roles" : ObjectId("5c0242621ab7b677e6b2e01e"), "__v" : 0 } ///role { "_id" : ObjectId("5c0242621ab7b677e6b2e01e"), "name" : "Admin" } Code: User

问题 I have two collections : Student { _id: ObjectId("657..."), name:'abc' }, { _id: ObjectId("593..."), name:'xyz' } Library { _id: ObjectId("987..."), book_name:'book1', issued_to: [ { student: ObjectId("657...") }, { student: ObjectId("658...") } ] }, { _id: ObjectId("898..."), book_name:'book2', issued_to: [ { student: ObjectId("593...") }, { student: ObjectId("594...") } ] } I want to make a Join to Student collection that exists in issued_to array of object field in Library collection. I

问题 I have a collection with documents that look like the following: { "_id" : ObjectId("55b377cb66b393427367c3e2"), "comment" : "This is a comment", "url_key" : "55b377cb66b393427367c3df", //This is an ObjectId from another record in a different collection } I need to find records in this collection that contain duplicate values for the both the comment AND the url_key. I can easily generate (using aggregate) duplicate records for the same, single, key (eg: comment), but I can't figure out how