MongoDB Schema

One of the major aspects of MongoDB is that it is a document store.  You can put anything you want into a document-- it is schema-less.  However, in many cases the documents stored in a collection do consist of the same fields.  So, in answer to the question, "how do I determine the schema of a collection?"  There are a couple options.

1. Manually/visually inspect the contents of the collection
2. Use a utility to examine a single document
3. Use some sort of utility to examine all of the documents in a collection

Manually inspecting the collection

As you can imagine is simply, "using" the database, and doing a db.collectionName.findOne()

For thoroughness, you'd probably want to examine more than one document.  This is where a db.collectionName.find().pretty() will come in handy.

Use a utility to examine a single document

I created a small python utility given a database name and collection name will give you the keys for a document in the collection.  This requires you have Python 2.7 and pymongo installed on your computer.  I put this in my ~/bin directory and chmod +x it.

	#!/usr/local/bin/python
	import sys
	from pymongo import MongoClient
	if len(sys.argv) < 3:
	print 'usage is: ' + sys.argv[0] + ' databaseName collectionName'
	sys.exit()
	dbName = sys.argv[1]
	collectionName = sys.argv[2]
	print 'Database: ' + dbName + ' Collection: ' + collectionName
	connection_string = "mongodb://localhost"
	connection = MongoClient(connection_string, safe=True)
	db = connection[dbName]
	collection = db[collectionName]
	document = collection.find_one()
	if document is not None:
	print 'document keys: '
	print document.keys()
	else:
	print '*** No Document Found ***'
	connection.disconnect()

view raw mongoGetKeys.py hosted with ❤ by GitHub

Use a utility to examine all of the documents in a collection

Skratch. has a cool extension to the MongoShell which examines all of the documents in a collection and tells you how many documents are using the field.  Fields can vary in type by document.  So, this tool even breaks down the occurrence of the field by type!  It is on github at: https://github.com/skratchdot/mongodb-schema/

MongoDB examples, Replica Set and GridFS

MongoDB Replica Set with Python example

I published a short lab on working with MongoDB replica sets in Python on GitHub https://github.com/k0emt/mongodb_repset_experiment

One thing to note is that I included all of the replica set nodes in the connection information.  That is because if "regular" primary node was down at the time of initial connection the code would fail.

The nodes in the replica set will figure out who should be primary and that will happen auto-magically behind the scenes.  However, your client code still needs to deal with needing to reconnect.

Adjust the counters if you want to have the client up and running longer while you experiment.

MongoDB GridFS with Java example

Example code for demonstrating GridFS and the metadata field with Java was also published on GitHub  https://github.com/k0emt/gridfs_example_java

By utilizing the metadata field you can keep your document metadata with it.