How should I store boolean values in mongodb?

Question

I see three main possibilities for storing boolean information in mongodb:

1. 0 or 1 as a String
2. 0 or 1 as a Number
3. True or False as a Boolean

What are the advantages/disadvantages of each method in terms of storage space used and the speed of queries?

Answer 1

Boolean is a native field type in BSON (MongoDB's server-side storage format, aka "Binary JSON"). Booleans use less storage than an integer or string and avoid any unexpected side effects of comparison.

For example, in a MongoDB find() query a string of "1" will not match a numeric value of 1 or a boolean value of true. If you want to store boolean values, definitely use a boolean type.

Comparing the BSON size (in bytes) in the mongo shell for completeness:

// Number (JavaScript double) - 8 bytes > var foo = { a: 1 } > Object.bsonsize(foo) 16  // UTF-8 String - 6 bytes > var foo = { a: '1'} > Object.bsonsize(foo) 14  // 32-bit int - 4 bytes > var foo = { a: NumberInt(1)} > Object.bsonsize(foo) 12  // Boolean - 1 byte > var foo = { a: true} > Object.bsonsize(foo) 9 

Note: the base size of the JSON object in the examples above (not counting the field values) is 8 bytes, so the difference between the reported Object.bsonsize() is the representation of the field value.