MongoDB field Growth

The document stored in MongoDB must have a "_id" key. The value of this key can be any type, and the default is a Objectid object.

ObjectId is a 12-byte BSON type data that has the following format:

• The first 4 bytes represent a timestamp
• The next 3 bytes are the machine identification code
• The immediate two bytes consist of a process ID (PID)
• The last three bytes are a random number.

Within a collection, each collection has a unique "_id" value to ensure that each document within the collection is uniquely identified.

MongoDB uses Objectid, not the main reason for other, more conventional practices, such as auto-incremented primary keys, because it is laborious and time consuming to automatically increase primary key values on multiple servers.

While MongoDB does not have auto-growing capabilities like SQL, in some cases we may need to implement OBJECTID auto-grow.

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

>db.createcollection ("counters")

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=  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:

12, "product_name": "Samsung S3", "category": "Mobiles"}

ObjectId is a 12-byte BSON type data that has the following format:

• The first 4 bytes represent a timestamp
• The next 3 bytes are the machine identification code
• The immediate two bytes consist of a process ID (PID)
• The last three bytes are a random number.

The document stored in MongoDB must have a "_id" key. The value of this key can be any type, and the default is a Objectid object.

Within a collection, each collection has a unique "_id" value to ensure that each document within the collection is uniquely identified.

MongoDB uses Objectid, not the main reason for other, more conventional practices, such as auto-incremented primary keys, because it is laborious and time consuming to automatically increase primary key values on multiple servers.

MongoDB field Growth