How can I discover a mongo database's structure

Just query the database by running the following commands in the mongo shell:

use mydb //this switches to the database you want to query
show collections //this command will list all collections in the database
db.collectionName.find().pretty() //this will show all documents in the database in a readable format; do the same for each collection in the database

You should then be able to examine the document structure.

There is actually a tool to help you out here called Variety:

http://blog.mongodb.org/post/21923016898/meet-variety-a-schema-analyzer-for-mongodb

You can view the Github repo for it here: https://github.com/variety/variety

I should probably warn you that:

• It uses MR to accomplish its tasks
• It uses certain other queries that could bring a production set-up to a near halt in terms of performance.

As such I recommend you run this on a development server or a hidden node of a replica or something.

Depending on the size and depth of your documents it may take a very long time to understand the rough structure of your database through this but it will eventually give one.

This will print name and its type

var schematodo = db.collection_name.findOne()
for (var key in schematodo) { print (key, typeof key) ; }