lookup

I find this comes up a lot, and I'm not sure the best way to approach it. The question I have is how to make the decision between using foreign keys to lookup tables, or using lookup table values directly in the tables requesting it, avoiding the lookup table relationship completely. Points to keep in mind: With the second method you would need to do mass updates to all records referencing the data if it is changed in the lookup table. This is focused more towards tables that have a lot of the column's referencing many lookup tables.Therefore lots of foreign keys means a lot of joins every

I have two collections: Games with schema: _id: ObjectId('gameId'), questions: [ { position: 1, question_id: ObjectId('baz') }, { position: 2, question_id: ObjectId('ban') }, ] Questions with schema: _id: ObjectId('baz'), text: 'FooBar' And now I'd like to join questions to games with adding to each question record value of question_position . So, I have query like this: db.games.aggregate([ { $lookup: { from: 'questions', localField: 'questions.question_id', foreignField: '_id', as: 'question_data', }, }]) Which return me all required info, with correct join according to questions array, _id:

Getting single key from Value I would like to do a backwards selection from the following JSON. I'd like to extract the abbreviation for a particular state. In this situation, the abbreviation is the key, and the value that I'm starting with is the value. Certainly I can loop through each value, comparing the value to my value, and select the key when the match is made. Is this the best way to approach something like this? Or is there a better way? Inverting JSON Data Another option would to invert this data early in processing to give myself a similar set of values with the keys/values

This question already has an answer here: Matching ObjectId to String for $graphLookup 1 answer I want to add join collections using $lookup in mongodb. I am trying as below { $lookup:{ from:"User", localField:"assignedId", foreignField:"_id", as:"dataa"} } Now I have two collections User contains objectid of users like "_id" : ObjectId("56ab6663d69d2d1100c074db"), and Tasks where it contains assignedId as a string "assignedId":"56ab6663d69d2d1100c074db" Now, when applying $lookup in both collection its not working because Id's are not matching. For that I googled it and found a solution that

I have two collections User { "_id" : ObjectId("584aac38686860d502929b8b"), "name" : "John" } Role { "_id" : ObjectId("584aaca6686860d502929b8d"), "role" : "Admin", "userId" : "584aac38686860d502929b8b" } I want to join these collection based on the userId (in role collection) - _id ( in user collection). I tried the below query: db.role.aggregate( { $lookup: { from: 'user', localField: 'userId', foreignField: '_id', as: 'output' } } ); This gives me expected results as long as i store userId as a ObjectId. When my userId is a string there are no results. Ps: I tried foreignField: '_id'