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I am beginning with mongodb and have a collection with documents that look like the following
{
"type": 1,
"tags": ["tag1", "tag2", "tag3"]
}
{
"type": 2,
"tags": ["tag2", "tag3"]
}
{
"type": 3,
"tags": ["tag1", "tag3"]
}
{
"type": 1,
"tags": ["tag1", "tag4"]
}
With this, I want a set of all the tags for a particular type. For example, for type 1, I want the set of tag1, tag2, tag3, tag4 (any order).
All I could think of is to get the tags and add them to a set in python, but I wanted to know if there is a way to do it with mongodb's mapreduce or something else. Please advise.
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What's the best way to keep track of unique tags for a collection of documents millions of items large? The normal way of doing tagging seems to be indexing multikeys.
To get unique values and ignore duplicates, use distinct() in MongoDB. The distinct() finds the distinct values for a specified field across a single collection and returns the results in an array.
MongoDB – Distinct() Method In MongoDB, the distinct() method finds the distinct values for a given field across a single collection and returns the results in an array. It takes three parameters first one is the field for which to return distinct values and the others are optional.
Find() Method. In MongoDB, find() method is used to select documents in a collection and return a cursor to the selected documents.
If you just want a (distinct) list of the tags then using distinct will be best. Map/Reduce will be slower and can't use an index for the javascript part.
http://docs.mongodb.org/manual/reference/method/db.collection.distinct/
db.coll.distinct("tags", {type:1}) Will return a set of tags for type=1.
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