I have a table like this
person = {
name : String,
favoriteFoods : [{type:Schema.Types.ObjectId, ref:'Food'}]
}
Q1: I would like to do the searching fast when I search for person with particular favourite food.
May I know if it is possible to index the favoriteFoods field and how to do it?
Q2: Alternatively, I would like to populate the favoriteFoods fields with Food content when I get back the person documents. May I know if there is command to do so?
Yes, you can index an array field. It's what's called a multikey index but in reality it's basically creating a normal index. Behind the scenes Mongo flattens the array and builds a separate index for each element.
For Q2 the easiest way to "populate" documents in Mongo is by using $lookup stage while aggregation, like so:
db.person.aggregate([
{
$match: {
name: "tom"
}
},
{
"$lookup": {
"from": "foods",
"localField": "favoriteFoods",
"foreignField": "_id",
"as": "favoriteFoods"
}
}
])
However if you first fetch the document you can just do a second db call to the other collection to populate your field, this is how mongoose does it for example with their populate option.