Difference between revisions of "MongoDB ObjectIds"
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ObjectID layout | ObjectID layout | ||
| − | 0 1 2 3 4 5 6 7 8 9 10 11 | + | {| border="1" cellpadding=2 cellspacing=2 |
| − | time machine pid inc | + | |Section 1|| |
| + | |0|1|2|3|4|5|6|7|8|9|10| 11| | ||
| + | |- | ||
| + | |time| machine |pid |inc| | ||
| + | |} | ||
Where: | Where: | ||
Revision as of 14:52, 21 October 2016
Main Page >> MongoDB >>MongoDB Workbook >> Object IDs
Object IDs
You may have noticed that the database creates an unique object for each document:
db.deptCollection.find().pretty()
Examine the output carefully and you will notice for each department in the collection something like:
"_id" : ObjectId("5808e3d2ec0ff55100af2649")
An ObjectId is like a primary key found in relational databases, except in this case it is globally unique across the whole database, not just one table. It is similar to objectIds found in object-oriented programming languages.
ObjectIds created by MongoDB consist of 12 bytes:
ObjectID layout
| Section 1 | 1|2|3|4|5|6|7|8|9|10| 11| | |
| machine |pid |inc| |
Where:
- time: system time
- machine: machine id
- pid: process id
- inc: incremental number
