I have a database structured like this:
I want to get all listItems, of all lists from a user with a x ID. What's the correct way of doing that?
I'm using node with mongoose, and I tried the following:
await User.findById(user._id).populate('list'); But realized that I can't populate all ListItem's from that. Meaning, I can't do this:
await User.findById(user._id).populate('list').populate('listItem'); How can I get all listItems, of all lists from a user with a x ID?
Assuming User, List, and ListItem are Collections, you should be able to accomplish this using $lookup..
Here is a live demo of the following query..
Query:
db.users.aggregate([ { $match: { uniqueId: 1 } }, { $lookup: { from: "lists", localField: "uniqueId", foreignField: "userId", as: "lists" } }, { $lookup: { from: "listItems", localField: "uniqueId", foreignField: "userId", as: "listItems" } } ]) Dataset:
db={ // Simulates a DB ******** "users": [ // Simulates a Collection ******** { "firstname": "John", "lastname": "Smith", "email": "[email protected]", "password": "password123", "uniqueId": 1 }, { "firstname": "Jane", "lastname": "Doe", "email": "[email protected]", "password": "123password", "uniqueId": 2 } ], "lists": [ // Simulates a Collection ******** { "userId": 1, "name": "Johns List 1", "items": [ 11, 12, 13 ] }, { "userId": 2, "name": "Groceries", "items": [ 21, 22, 23 ] } ], "listItems": [ // Simulates a Collection ******** { "userId": 2, "itemId": 21, "title": "Apple", "notes": [] }, { "userId": 2, "itemId": 22, "title": "Banana", "notes": [] }, { "userId": 2, "itemId": 23, "title": "Strawberry", "notes": [] }, { "userId": 1, "itemId": 11, "title": "Oil Change", "notes": [] }, { "userId": 1, "itemId": 12, "title": "Pick Up Grandma", "notes": [] }, { "userId": 1, "itemId": 13, "title": "Go For Run", "notes": [] } ] } Result:
[ { "_id": ObjectId("5a934e000102030405000008"), "email": "[email protected]", "firstname": "John", "lastname": "Smith", "listItems": [ { "_id": ObjectId("5a934e000102030405000003"), "itemId": 11, "notes": [], "title": "Oil Change", "userId": 1 }, { "_id": ObjectId("5a934e000102030405000004"), "itemId": 12, "notes": [], "title": "Pick Up Grandma", "userId": 1 }, { "_id": ObjectId("5a934e000102030405000005"), "itemId": 13, "notes": [], "title": "Go For Run", "userId": 1 } ], "lists": [ { "_id": ObjectId("5a934e000102030405000006"), "items": [ 11, 12, 13 ], "name": "Johns List 1", "userId": 1 } ], "password": "password123", "uniqueId": 1 } ] 
populate method in Mongoose relies heavily on your defined Mongoose schema. It is possible to accomplish using the code you have provided in your question, if the schema is properly defined. You can read more here on Mongoose schema/populate. I can test this out tomorrow and get back to you.