MongoDB Shell Collection Methods

Following are the MongoDB collection methods that are used in different scenarios.

#1: db.collection.aggregate(pipeline, option)

The aggregate method calculates mass values for the data in a collection/table or in a view.

Pipeline: It is an array of mass data operations or stages. It can accept the pipeline as a separate argument, not as an element in an array. If the pipeline is not specified as an array, then the second parameter will not be specified.

Option: A document that passes the aggregate command. It will be available only when you specify the pipeline as an array.

Command Fields:

Example

The examples use the collection library that contains the following documents:

Calculating the sum

Output:

Specifying the collation

#2 db.collection.bulkWrite()

The bulkWrite() method performs multiple write operations with the order of execution control. Array of write operations are executed by this operation. Operations are executed in a specific order by default.

Syntax:

Output:

Execution of Operations

insertOne: It inserts only one document into the collection.

Update one: It updates only one document that matches the filter in the collection.

Output:

Update Many: It updates all the filter matched documents in the collection.

replaceOne: It replaces a single document in the collection that matches the filter.

# 3. db.collection.count(query, option)

The count() method return the number of documents that would match a find method query for the collection or view.

Example:

We will count all the document in the javaTpoint collection using the following operation:

Now, we will count all the documents that Match a Query in the javaTpoint collection with the field tut_dt greater than new Date ('01/01/2015')

Output:

#4. Db.collection.countDocuments(query, options)

The countDocument() method return the number of documents that match the query for a collection or view. it does not use the metadata to return the count.

Syntax:

Examples:

Below example will count the number of all the documents in the javaTpoint collection.

Now, we will count all the documents that Match a Query in the javaTpoint collection with the field tut_dt greater than new Date ('01/01/2015')

#5. db.collection.estimatedDocumentCount()

The estimateddocumentCount() method counts all documents in a collection or view. This method wraps the count command.

Syntax:

Example

The following example will retrieve the count of all the documents in the javaTpoint collection:

#6. db.collection.createIndex()

It can create the indexes on collections

Syntax:

Keys: For an ascending index on a field we need to specify a value of 1 and for the descending index we need to specify a value of -1.

Example

The example below creates an ascending index on the field tut_Date.

The following example shows a compound index created on the tut_Date field and the tut_code field.

The example below will create an index named as category_tutorial. The example creates the index with the collation that specifies the locale fr and comparison strength.

#7. db.collection.createIndexes()

The createIndexes() method creates one or more indexes on a collection.

Syntax:

Keypatterns: It is an array that contains the index specific documents. All the document have field-value pairs. For an ascending index on a field we need to specify a value of 1 and for the descending index we need to specify a value of -1

Example

In the example below we considered a employee collection containing documents that resemble the following:

Output:

Now, the example below creates two indexes on the products collection:

• Index on the manufacturer field in ascending order.
• Index on the category field in ascending order.

The above indexes use a collation which specifies the basic fr and comparison strength  as 2.

#8. db.collection.dataSize()

The data size method have a cover around the output of the collStats (i.e. db.collection.stats() ) command.

#9. db.collection.deleteOne()

The deleteOne() method deletes one document from the collection. It replaces the first document that is similar to the filter. You need to use a field that is related to a unique index such as id for perfect deletions.

Syntax:

Example

The orders collection has documents with the following structure:

The following operation deletes the order with _id: objectId ("563237a41a4d6858 2da"):

Output: