## Comparison/Sort Order 

When comparing values of different BSON types, MongoDB uses the following comparison order, from lowest to highest: 

1. MinKey (internal type) 

2. Null 

3. Numbers (ints, longs, doubles) 

4. Symbol, String 

5. Object 

6. Array 

7. BinData 

8. ObjectId 

9. Boolean 

10. Date 

11. Timestamp 

12. Regular Expression 

13. MaxKey (internal type) 

MongoDB treats some types as equivalent for comparison purposes. For instance, numeric types undergo conversion before comparison. 

Changed in version 3.0.0: Date objects sort before Timestamp objects. Previously Date and Timestamp objects sorted together. 

The comparison treats a non-existent field as it would an empty BSON Object. As such, a sort on the a field in documents { } and { a: null } would treat the documents as equivalent in sort order. 

With arrays, a less-than comparison or an ascending sort compares the smallest element of arrays, and a greater-than comparison or a descending sort compares the largest element of the arrays. As such, when comparing a field whose value is a single-element array (e.g. [ 1 ] ) with non-array fields (e.g. 2 ), the comparison is between 1 and 2 . A comparison of an empty array (e.g. [ ] ) treats the empty array as less than null or a missing field. 

MongoDB sorts BinData in the following order: 

1. First, the length or size of the data. 

2. Then, by the BSON one-byte subtype. 

3. Finally, by the data, performing a byte-by-byte comparison. 

The following sections describe special considerations for particular BSON types. 

## ObjectId 

ObjectIds are: small, likely unique, fast to generate, and ordered. These values consists of 12-bytes, where the first four bytes are a timestamp that reflect the ObjectId’s creation. Refer to the ObjectId (page 176) documentation for more information. 

