Return documents matching field array

Question

Using Mongoose with MongoDB, I need to return a series of lookups based on a field of an initial lookup. My Schema is as follows:

var PartSchema = new Schema({
    partcode: String,
    children: [String]
});

And the data looks like the following:

[{"partcode":"A1","children":["B1","B2","B3","B4"]},
 {"partcode":"B1","children":["C11","C21","C31","C41"]},
 {"partcode":"B2","children":["C12","C22","C32","C42"]},
 {"partcode":"B3","children":["C13","C23","C33","C43"]},
 {"partcode":"B4","children":["C14","C24","C34","C44"]}]

I can query for A1's children field by using the following static call:

var childrenOnly =
  {children: 1, _id: 0};
PartSchema.static('getChildren', function (partcode, callback) {
  return this.find({ partcode: partcode }, childrenOnly, callback);
});

This returns (via express)

[{"children":["B1","B2","B3","B4"]}]

What I need it to return is

[{"partcode":"B1","children":["C11","C21","C31","C41"]},
 {"partcode":"B2","children":["C12","C22","C32","C42"]},
 {"partcode":"B3","children":["C13","C23","C33","C43"]},
 {"partcode":"B4","children":["C14","C24","C34","C44"]}]

I'm guessing an iterative call is required with the first query returning the children array, and then iterating over the children array to get each of the child records.

chridam · Accepted Answer · 2015-05-05 12:32:09Z

1

The general idea is to first try getting the array with the children codes using the findOne() method and then use that array as the query with the $in operator in the find() method to return the full result.

var childrenOnly = {children: 1, _id: 0};
PartSchema.static('getChildren', function (partcode, callback) {
    var self = this;
    this.findOne({ partcode: partcode }, childrenOnly)
        .exec(function (err, doc) {
             console.log(doc.children); // {"children":["B1","B2","B3","B4"]}
             return self.find({"partcode": {"$in": doc.children} }, callback);
        });
});

-- EDIT --

Look into using promises. I haven't tested this yet but I believe it should also do the trick:

var childrenOnly = {children: 1, _id: 0};
PartSchema.static('getChildren', function (partcode, callback) {
    var self = this,
        promise = this.findOne({ partcode: partcode }, childrenOnly).exec();
    promise.then(function (doc) {
        return self.find({"partcode": {"$in": doc.children} }, callback);            
    });               
});

edited May 5, 2015 at 12:32

answered May 5, 2015 at 11:38

chridam

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6 Comments

Terry Over a year ago

I added a variable var self = this; before the this.findone (which I changed to self.findone) and then called return self.find({"partcode": {"$in": doc.children} }, exclId, callback);. This works and seems sensible. If this is idiomatic, I'll accept an answer that uses it. Thanks for all your help!

chridam Over a year ago

@Terry Nice one! Initially thought of adding that but decided to use promises instead. That should be the solution. Nonetheless I will shortly update my answer yet again to reflect this.

Terry Over a year ago

Thanks Chridam - appreciate your help.

chridam Over a year ago

@Terry No worries, happy to be of help.

Terry Over a year ago

Both options work perfectly. The Promises version feels more idiomatic, and that's the one I'll go with. Again, thanks for all your help.

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