I was trying to fetch distinct tags from array for auto-complete module. The collection format is:
{
tags:["apple","mango","apple-pie"]
},
{
tags: ["man","lemon","lemon-lite"]
}
Now, I am interested in getting distinct tags, with prefix q.
The query that I triggered is:
db.portfolio.distinct("tags",{"tags":/app/});
However, this query returned entire array:
["apple","mango","apple-pie"].
My requirement is: ["apple", "apple-pie"].
How can I modify my query to get desired result?
You can do this with aggregation.
$unwind the tags array.$match those tags you are looking for according to the regular expression given.$group the tags into a set using $addToSet.The code looks something like this:
> db.portfolio.aggregate([
{ "$unwind": "$tags" },
{ "$match": { "tags": /app/ }},
{ "$group":
{
"_id": null,
"tags": { "$addToSet": "$tags" }
}
}
]);
{ "_id" : null, "tags" : [ "apple-pie", "apple" ] }
Not possible with distinct because query will return documents containing matching tags(/app/) which mean there will be non matching tags as well. distinct gets a distinct set from all these tags. So you will have to filter the returning array again( using regex /app/)
