I am creating a project using Node.js, where I have two models: User and Project.

Here's the Schema for Project model:

const ProjectSchema = new mongoose.Schema({
    name: {
        type: String,
        maxlength: 50,
        required: true,
    },
    description: {
        type: String,
        maxlength: 800,
        required: true
    },
    contributors: [{
        type: mongoose.Schema.Types.ObjectId,
        ref: "User"
    }],
});

Now, for a project, I want to check if the current user is already present in the project's contributors. If the user is not present, then add the user, otherwise, Ignore.

How can I check that in an efficient manner?

CodePudding user response：

mongoose offers you the aggregate method which does pretty everything, in your case:

const projects = ProjectModel.aggregate([
  { $match: {/* query for matching a small size of projects first(you should definitely do this) */} },
  { $unwind: "$contributors" },
  { $project: { contributor: "$contributors" } }, // This stage is actually optional
  { $match: { "contributor._id": /* contributor id you want to check */ } },
  { $count: "projects" }
]);

Now you can just check the variable and see how many projects have the user in their contributors array

I tested this dataset:

[{
  "_id": 1,
  "name": "Project1",
  "contributors": [{
      "_id": 11,
      "name": "user1"
    }, {
      "_id": 22,
      "name": "user2"
    }]
}, {
  "_id": 2,
  "name": "Project2",
  "contributors": [{
      "_id": 22,
      "name": "user3"
    }, {
      "_id": 44,
      "name": "user4"
    }]
}]

With this query:

const projects = ProjectModel.aggregate([
  { $match: { _id: 1 } },
  { $unwind: "$contributors" },
  { $project: { contributor: "$contributors" } },
  { $match: { "contributor._id": 22 } },
  { $count: "projects" }
]);

The result:

[{
  "projects": 1
}]

Playground Link

CodePudding user response：

Query

• find the project
• check if user _id is on the contributors array
• if it is do nothing (keep old value)
• else add the new user
• replace 2 with the user id and {"_id": 2} with the user document

*there is no performance problem here, it will be max 1 project i guess with that _id , you only do 1 test to see if its already contributor.

Test code here

update(
{"_id": {"$eq": 1}},   //find the project
[{"$set": 
    {"contributors": 
      {"$cond": 
        [{"$in": [2, "$contributors._id"]}, "$contributors",
          {"$concatArrays": ["$contributors", [{"_id": 2}]]}]}}}])