Difference between revisions of "MongoDB ObjectIds"
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"_id" : ObjectId("5808e3d2ec0ff55100af2649") | "_id" : ObjectId("5808e3d2ec0ff55100af2649") | ||
</pre> | </pre> | ||
| + | |||
| + | 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 | ||
| + | |||
| + | 0 1 2 3 4 5 6 7 8 9 10 11 | ||
| + | time machine pid inc | ||
| + | |||
| + | Where: | ||
| + | * time: system time | ||
| + | * machine: machine id | ||
| + | * pid: process id | ||
| + | * inc: incremental number | ||
Revision as of 13:50, 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
0 1 2 3 4 5 6 7 8 9 10 11 time machine pid inc
Where:
- time: system time
- machine: machine id
- pid: process id
- inc: incremental number
