mongodb-schema

Extends the DBCollection object in the mongo shell to infer the schema of a MongoDB collection.

This is an early prototype. Use at your own risk.

Installation

Two ways to invoke the script.

1. Load the script directly (one-time usage)

This will load the mongodb-schema.js and the open the shell as usual. You will have to add the script every time you open the shell.

mongo mongodb-schema.js --shell

2. Load the script via the .mongorc.js file (permanent usage)

You can also add the following line to your ~/.mongorc.js file to always load the file on shell startup (unless started with --norc):

load('/<path-to>/mongodb-schema.js')

Replace the <path-to> part with the actual path where the mongodb-schema.js is located.

Usage

Basic Usage

The script extends the DBCollection object to have another new method: .schema(). On a collection called foo, run it with:

db.foo.schema()

This will use the first 100 (by default) documents from the collection and calculate a probabilistic schema based on these documents.

Example of schema:

{
    "$c": 100,
    "_id": {
        "$c": 100,
        "$p": 1, 
        "type": "ObjectId"
    },
    "a": {
        "$c": 100,
        "$p": 1,
        "b": {
            "$c": 100,
            "$p": 1,
            "$type": "number"
        },
        "c": {
            "$c": 70,
            "$p": 0.7,
            "$type": "string"
        }
    }
}

Usage with options

You can pass in an options object into the .schema() method. Currently it supports 2 options: numSamples and flat.

db.foo.schema( {numSamples: 20, flat: true} )

This will use the first 20 documents to calculate the schema and return the schema as flat object (all fields are collapsed to the top with dot-notation).

Example of flat schema:

{
    "$c": 20,
    "_id": {
        "$c": 20,
        "$p": 1, 
        "type": "ObjectId"
    },
    "a.b": {
        "$c": 20,
        "$p": 1,
        "$type": "number"
    },
    "a.c": {
        "$c": 13,
        "$p": 0.65,
        "$type": "string"
    }
}