This document provides tips and tricks for using the MongoDB shell, including: - The shell allows running Javascript and accessing MongoDB functions and objects - It can be used for debugging queries, testing, and administration - However, Javascript numbers and dates can be confusing to work with in the shell - Functions like load(), runCommand(), getProfilingLevel() and forEach() provide useful shell capabilities - The shell is generally slower than queries run directly on the server

1. #MongoDBDays
MongoDB Shell Tips &
Tricks
Mike Friedman
Perl Engineer & Evangelist, 10gen

2. What is the Shell?
Embedded • vars
Javascript • functions
Interpreter • data structs + types
• ObjectId("...")
Global Functions • new Date()
and Objects • Object.bsonsize()
MongoDB driver • db["collection"].find/count/update
Exposed • short-hand for collections
• Doesn't require quoted keys
JSON-like stuff • Don’t copy and paste too much

3. MongoDB Shell: Advantages
• Debugging Queries / Syntax
• Testing
• Administration
• Scripting Glue

4. MongoDB Shell: Disadvantages
• Numbers in JS are a pain
– 32/64-bit int/long  NumberInt() / NumberLong()
– Primitive numbers are all 64-bit FP doubles
• Dates can be confusing
– new Date( "1/1/1" )
– new ISODate( ... )
NOT: Date( "1/1/1" )  string

5. Speed Considerations
• Shell
– JavaScript is slow
– Always in "write-acknowledged" (safe mode) / GLE
– Data Conversions
• Server
– Applies on the server as well
– Careful with round-tripping numbers

6. Insert, Update, Remove
for ( i = 0; i < 1000; i++ ) {
db.test.insert( {
x: i,
ts: new Date()
} );
}

7. Loading Scripts
• Commandline
– --eval switch
– .js files
• Within the shell
– load()

8. Running Commands
• db.runCommand( { ... } )
– Runs any arbitrary command against the current DB
• db.adminCommand( { ... } )
– Run commands against the admin database

9. db.adminCommand
Definition
function (obj) {
if (this._name == "admin") {
return this.runCommand(obj);
}
return this.getSiblingDB("admin")
.runCommand(obj);
}

10. Profiling
• setProfilingLevel( lvl, <ms> )
– 0: none
– 1: time-based
– 2: all
• getProfilingLevel()
• Reading from the profile collection
– db.system.profile.find()

11. Cool Functions
• printjson  tojson
• forEach on arrays, queries, and cursors

12. forEach example
[{x:1},{y:1}].forEach(function(x) {
printjson(x)
})
{ "x" : 1 }
{ "y" : 1 }

13. Cool Functions
• printjson  tojson
• forEach on arrays, queries, and cursors
• Object.bsonsize
• load(file)
• run(file)

14. Print all Indexes
db.getCollectionNames().
forEach( function(x) {
print( "Collection: " + x );
printjson( db[x].getIndexes() );
})

15. Getting the Biggest Doc
var cursor = db.coll.find();
var biggest = 0;
var doc = {};
cursor.forEach(function (x) {
var size = Object.bsonsize(x);
if (size > biggest) {
biggest = size;
doc = x;
}
});

16. #MongoDBDays
Thank You
Mike Friedman
Perl Engineer & Evangelist, 10gen