Difference between revisions of "MongoDB ObjectIds"

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ObjectID layout
 
ObjectID layout
  
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{| border="1" cellpadding=2 cellspacing=2
time machine pid inc  
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|Section 1||
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|0|1|2|3|4|5|6|7|8|9|10| 11|
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|-
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|time| machine |pid |inc|
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|}
  
 
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