MongoDB Auto Grow

MongoDB does not have auto-growth functions like SQL, and MongoDB's _id is a 12-byte unique identifier that is automatically generated by the system.

In some cases, however, we may need to implement the OBJECTID auto-grow feature.

Since MongoDB does not implement this function, we can do it programmatically, the following we will implement the _id field automatically grow in the Counters collection.

Using the Counters Collection

Consider the following products documentation. We want the _id field to implement the auto-grow function from 1,2,3,4 to N.

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

To do this, create a counters collection where the sequence field values can be automatically long:

>db.createcollection ("counters")

Now we insert the following document into the counters collection, using ProductID as the key:

{  "_id": "ProductID",  "Sequence_value": 0}

The Sequence_value field is a value after the sequence is automatically grown.

Use the following command to insert the counters collection in the sequence document:

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

Creating Javascript Functions

Now, we create the function Getnextsequencevalue as input to the sequence name, and the specified sequence automatically grows by 1 and returns the latest sequence value. In the example in this article, the sequence is named ProductID.

>function Getnextsequencevalue (sequencename) {   var sequencedocument = db.counters.findAndModify (      {         Query:{_id:sequencename},         update: {$inc: {sequence_value:1}},         new:true      });   return sequencedocument.sequence_value;}

Using Javascript functions

Next we will use the Getnextsequencevalue function to create a new document and set the document _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 the _id field.

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

>db.prodcuts.find ()

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

{"_id": 1, "product_name": "Apple iPhone", "category": "Mobiles"} {"_id": 2, "product_name": "Samsung S3", "category": "Mobiles"}

MongoDB Auto Grow