Difference between revisions of "MongoDB ObjectIds"
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== Adding ObjectIds == | == Adding ObjectIds == | ||
| − | You can assign an objectId yourself to a document, but you do need to ensure it will be globally unique, so treating it as a primary key is not a good idea. | + | You can assign an objectId yourself to a document, but you do need to ensure it will be globally unique, so treating it as a primary key is not a good idea. Alternatively, you can use the '''ObjectId()''' function to add one. |
| − | + | The following examples creates a new projectCollection, with two projects: | |
| − | + | db.projCollection.insert( | |
| − | db. | + | { |
| − | + | _id: 10, | |
| − | + | projno: 110, | |
| − | + | proj_name: 'Oracle Project', | |
| − | + | budget: 10000, | |
| − | + | } | |
| − | + | ) | |
| − | + | ||
| − | + | db.projCollection.insert( | |
| − | + | {_id: 20, | |
| − | + | projno: 120, | |
| − | + | proj_name: 'MongoDB Project', | |
| − | + | budget: 20000, | |
| − | + | } | |
| − | + | ) | |
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== Querying with ObjectIds == | == Querying with ObjectIds == | ||
Revision as of 19:40, 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 are a 12-byte BSON type, with the following structure:
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| time | machine | pid | inc | ||||||||
Where:
- time: timestamp - the time in seconds
- machine: machine identifier
- pid: process identifier
- inc: auto-incrementing counter
Adding ObjectIds
You can assign an objectId yourself to a document, but you do need to ensure it will be globally unique, so treating it as a primary key is not a good idea. Alternatively, you can use the ObjectId() function to add one.
The following examples creates a new projectCollection, with two projects:
db.projCollection.insert(
{
_id: 10,
projno: 110,
proj_name: 'Oracle Project',
budget: 10000,
}
)
db.projCollection.insert(
{_id: 20,
projno: 120,
proj_name: 'MongoDB Project',
budget: 20000,
}
)
Querying with ObjectIds
db.deptCollection.find({ "employees._id" : ObjectId("580a0e5bf090aeb82af5566c")}).pretty()
Still returns whole array!
Updates with ObjectIds
The objectId can be used to update a record. For example, we want to update employee 2222.
