MongoDB grows automatically

MongoDB grows automatically

MongoDB does not have the same auto-growth capabilities as SQL, and MongoDB's _id is the system's automatically generated 12-byte unique identity.

However, in some cases, we may need to implement ObjectId auto-growth.

Since MongoDB doesn't do this, we can do it programmatically, and we'll automatically grow the _id in the counters collection.

Use the counters collection

Consider the following products documentation. We _id the automatic growth from 1,2,3,4 to n in the field.

{
  "_id":1,
  "product_name": "Apple iPhone",
  "category": "mobiles"
}

To do this, create a set of counters, and the sequence field values can be automatically long:

>db.createCollection("counters")

Now let's insert the following document into the counters collection, using productid as key:

{
  "_id":"productid",
  "sequence_value": 0
}

sequence_value field is a value after the sequence grows automatically.

Insert the sequence document of the counters collection with the following command:

>db.counters.insert({_id:"productid",sequence_value:0})

Create a Javascript function

Now that we create the function getNextSequenceValue as input to the sequence name, the specified sequence automatically increases by 1 and returns the latest sequence value. In the instance of this article, the sequence is called productid.

>function getNextSequenceValue(sequenceName){
   var sequenceDocument = db.counters.findAndModify(
      {
         query:{_id: sequenceName },
         update: {$inc:{sequence_value:1}},
         new:true
      });
   return sequenceDocument.sequence_value;
}

Use Javascript functions

Next we'll create a new document using the getNextSequenceValue function and set the _id automatically for the returned sequence value:

>db.products.insert({
   "_id":getNextSequenceValue("productid"),
   "product_name":"Apple iPhone",
   "category":"mobiles"})

>db.products.insert({
   "_id":getNextSequenceValue("productid"),
   "product_name":"Samsung S3",
   "category":"mobiles"})

As you can see, we use the getNextSequenceValue function to set _id field.

To verify that the function is valid, we can read the document using the following command:

>db.prodcuts.find()

The above command returns the following results, and we _id that the field is self-growing:

{ "_id" : 1, "product_name" : "Apple iPhone", "category" : "mobiles"}

{ "_id" : 2, "product_name" : "Samsung S3", "category" : "mobiles" }