MongoDB Auto-Increment Sequence

MongoDB does not have a built-in automatic increment feature like SQL databases. By default, it will_idfield12The byte ObjectId is used as the primary key to uniquely identify the document. However, in some cases, we may want the _id field to have some automatically incremented values in addition to ObjectId.

Since this is not a default feature in MongoDB, we will use}}countersProgrammatically implement this function as recommended by the MongoDB document collection.

Use the counters collection

See the followingproductsdocument. We hope the _id field is an auto-incrementing integer starting from1,2,3,4to n auto-incrementing integer sequence.

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

To do this, create acounterscollection, which will track the last sequence value of all sequence fields.

>db.createCollection("counters")

Now, we will create the following documentproductidinsert it as a key into the counters collection-

> db.counters.insert({
	"_id":"productid",
	"sequence_value": 0
)
WriteResult({ "nInserted":　1　)
>

Use the following code to insert this sequence document into the counters collection-

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

Create a Javascript function

Now, we will create a functiongetNextSequenceValue，the function takes the sequence name as input, and increments the sequence number by1and return the updated sequence number. In our example, the sequence name isproductid。

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

Use the Javascript function

Now, we will use the getNextSequenceValue function when creating a new document and assigning the returned sequence value to the document's _id field.

Insert the following code to insert two sample documents-

>db.products.insert({
　　　"_id": getNextSequenceValue("productid"),
　　　"product_name":"Apple iPhone",
　　　"category": "mobiles"
)
>db.products.insert({
　　　"_id": getNextSequenceValue("productid"),
　　　"product_name": "Samsung S"3,
　　　"category": "mobiles"
)

As you can see, we used the getNextSequenceValue function to set the value of the _id field.

To verify the functionality, let's use the find command to retrieve the document-

>db.products.find()

The query above returned the following documents with an auto-incrementing _id field-

{ "_id":　1, "product_name": "Apple iPhone", "category": "mobiles"
{ "_id":　2, "product_name": "Samsung S"3"category": "mobiles"