如何访问 mongoDB 集合中特定文档的特定属性？

Question

To summarize, I am working with 2 collections - 'usercollection' and 'groupcollection' and I would like to associate users with groups. I don't want to have 2 copies of all the user documents so I have a unique ID attribute for each user that I want to use to associate specific users with specific groups. This is all running on a localhost webserver so I'm getting the input from an html page with a form in it where you enter 'username' and 'groupname'. I tried using the.distinct() function with query as 'username' and the target field/attribute as 'uid'.

    // Set our internal DB variable
    var db = req.db;

    // Get our form values. These rely on the "name" attributes
    var userName = req.body.username;

    // Set query and options for searching usercollection
    var query = {"username" : userName};
    const fieldName = "uid";

    // Set our collections
    var users = db.get('usercollection');

    // Get UID corresponding to username
    var uidToAdd = users.distinct(fieldName, query);

This is what I attempted (with some other lines that aren't relevant taken out) but it just returned a null object so I'm at a bit of a loss. Also, I'm still a beginner with nodejs/javascript/mongoDB so the more informative the answer the better! When I do the same code in the mongo shell I can get the actual value of the 'uid' attribute so I really don't know what's going wrong

Answer 1

I am not sure I am following you. But if I understood correctly, if you want to make a relationship between ' usercollection ' and ' groupcolletion ', you can simply create those 2 collections and each user in ' usercollection ' should have a field with ' groupid ' as a reference. In this way, you can access ' groupcollection ' easily.

Here is an example with using mongoose.

In User model

...

groupId: {
 type: mongoose.Schema.Types.ObjectID
 ref: "Group"
}

...

Later you can also use ' populate ' to fetch ' Group ' information.

...

let data = await User.findById(id).populate('groupId');

...