count - Get number of documents per field in MongoDB, like Studio3T Schema operation

Question

How do I obtain the distribution of fields among a MongoDB collection, i.e the total count of documents for each field (without knowing the fields)??

E.g. considering these documents?:

{ "doc": { "a": …, "b": … } }
{ "doc": { "a": …, "c": … } }
{ "doc": { "a": …, "c": …, "d": { "e": … } } }

I would like to get

{ "a": 3, "b": 1, "c": 2, "d": 1, "d.e": 1 }

Studio3T has a "Schema" feature which does exactly that (and a bit more) for a random sample of the DB, how is the query constructed??

question from:https://stackoverflow.com/questions/65944571/get-number-of-documents-per-field-in-mongodb-like-studio3t-schema-operation

Answer 1

One way is to use db.collection.countDocuments() with the $exists operator:

db.collection.countDocuments({ a: { $exists: true});
db.collection.countDocuments({ b: { $exists: true});
db.collection.countDocuments({ c: { $exists: true});