Mongoose populate() returns array of objects instead of single object

Question

I have a collection which has a attribute which references an objectId of another collection.

placeSchema = mongoose.Schema({
    name: String,
    category: [{ type: Schema.Types.ObjectId, ref: 'categories' }],
    facilities: [{ type: Schema.Types.ObjectId, ref: 'facilities' }],
});

the category ref is an objectId of the categories collection. The facilities ref is an array of objectId's of the facilities collection.

When I populate the attributes, facilities becomes and array of the facilities objecrts but category also becomes an array of one single category .

Place.find(query).populate('category').populate('facilities').limit(limit).skip(offset).exec(function(err, data){
    if (err) return handleError(err);
    res.json(data);
});

Here's an example of the above query:

{
    "_id": "52ff59be70e8f0dfc8358cb4",
    "address": {
        "address_1": "Chambers Street",
        "city": "Edinburgh",
        "postcode": "EH1 1JF"
    },
    "description": "The National Museum of Scotland brings together our rich Scottish heritage with exciting international collections.",
    "loc": {
        "lon": -3.188384,
        "lat": 55.94772
    },
    "name": "National Museum of Scotland",
    "facilities": [
        {
            "_id": "53012d5b65b5e9a35efbb214",
            "name": "Facility One"
        },
        {
            "_id": "53012d6965b5e9a35efbb215",
            "name": "Facility Two"
        }
    ],
    "category": [
        {
            "_id": "52ffbf33605d0c81f36d98e0",
            "name": "Museums",
            "slug": "museums"
        }
    ]
}

Here's the document as it is in Mongo:

{
    "_id" : ObjectId("52ff59be70e8f0dfc8358cb4"),
    "address" : {
        "address_1" : "Chambers Street",
        "city" : "Edinburgh",
        "postcode" : "EH1 1JF"
    },
    "category" : ObjectId("52ffbf33605d0c81f36d98e0"),
    "description" : "The National Museum of Scotland brings together our rich Scottish heritage with exciting international collections.",
    "facilities" : [
        ObjectId("53012d5b65b5e9a35efbb214"),
        ObjectId("53012d6965b5e9a35efbb215")
    ],
    "loc" : {
        "lon" : -3.188384,
        "lat" : 55.94772
    },
    "name" : "National Museum of Scotland"
}

How do I populate my single category ref instead of an array?

Answer 1

It makes sense since you in the schema definition have declared the category field to be an array:

category: [{ type: Schema.Types.ObjectId, ref: 'categories' }]

The following should work to not put it in an array (remove the [] ):

category: { type: Schema.Types.ObjectId, ref: 'categories' }

That is assuming that you indeed want only one category.