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Check Count, Delete Documents and Drop Collections in MongoDB

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Checking the count of documents from collection in MongoDB:

In RDBMS, to check the count from table, we need to use count function. In MongoDB also, we have count() method to get the count from collection.

 Syntax:

 db.<Collection Name>.count()

Example:

db.FirstCollection.count(). This query will return the count of total number of records.

To get the count of records with specific filter then we need to use find() metho along with count().

Let's say we have records with different Student_Id values in StudentData collection. And we have to find the number of records with Student_Id 201. To do this, we have to pass below query.

db.StudentData.find({"Student_Id":201}).count()


Delete Documents in MongoDB:

In RDBMS, to delete data from table, we need to use DELETE statements.As MongoDB is noSQL database, we have to use remove() method to delete data from collection.

Syntax:

db.<Collection Name>.remove({<data selection criteria>},{<justOne: true or flase>})

to remove() method, we need to pass the query to select the data from collection to delete. Here, another option is there to limit the delete to one record. If you set "justOne" to true then it will delete only one record. This is optional.

Example:

Assume, i have a collection FirstCollection and I have records with Student_Id 201. I need to delete these records from collection.

db.FirstCollection.remove({"Student_ID":201})

The above query will delete all the records with the Student Id 201. In the above query, "{"Student_ID":201}" is data selection criteria to delete from collection.


To remove only one record, then pass true to the key "justOne".

db.FirstCollection.remove({"Student_ID":201},{justOne:true})


Drop collection in MongoDB:

In RDBMS, to delete data from table, we need to use DROP statements.As MongoDB is noSQL database, we have to use drop() method to delete data from collection.

Syntax:

db.<Collection Name>.drop()

This will drop the mentioned collection from the database,

Example:

Assume that you have to delete FirstCollection collection from database. to do this, you have to pass below command:

db.FirstCollection.drop()

drop() method will return "true" if collection dropped successfully. If collection does not exist to drop then drop() method will return "false".

You can see the video in the bellow link:
https://www.youtube.com/watch?v=mV11JykX1T8

Hope this is helpful.

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