How to define aliases in the MongoDB Shell?

Question

I'm using the MongoDB shell and like to define some shortcuts. For example, it would be nice to abbreviate show databases with sd.

I already managed to add a function hw() to the MongoDB shell by adding it's definition to the ~/.mongorc.js:

function hw() {
    print("Hello World.");
}

When I type hw() in the mongo-shell, it prints out Hello World.

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Question 1: Is it also possible to execute the function without having to type the brackets (i.e. hw instead of hw())?

I tried to bind the function to variable using anonymous functions, but still I have to type brackets, otherwise the definition of the function is printed out

hw=function(){ print("Hello World (anonymous)."); };

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Question 2: How can I execute MongoDB commands from within my functions? I tried:

function sd() {
    show databases;
}

but that gives an error during startup of the MongoDB shell:

SyntaxError: Unexpected identifier at /home/edward/.mongorc.js:2

Answer 1

To list databases try :

function sd(){
     return db._adminCommand( { listDatabases: 1 } ) 
}

Basically you have to run valid javascript here. Remember that you have to run these in context of admin database - runCommand will not be enough - you have to use _adminCommand here.

For other commands see http://docs.mongodb.org/manual/reference/command/

if you would like to get rid of parenthesis there is also a way (you would have to put property on 'this')

Object.defineProperty(this, 'sd', {
    get: function() { 
        return db._adminCommand( {listDatabases: 1} )
    },
    enumerable: true,
    configurable: true
});

Answer 2

Another way to alias databases in the mongo shell is to use the db.getSiblingDB() command. In the following, imagine you have two MongoDB databases - AmazonSales and EbaySales. Both the databases have a users collection. You can now use the aliases as described below in the Mongo shell, instead of always needing the 'use ' command to switch context

var cs = db.getSiblingDB('AmazonSales')
cs.users.count()
cs.users.find({name:'John'})

var r = db.getSiblingDB('EbaySales')
r.users.count()