Removing Documents: MongoDB

Lets learn how to remove documents from the collection using remove() and drop() methods.

test database, names collection

> db.names.find().pretty()
{
        "_id" : ObjectId("53c6392a2eea8062e084cb57"),
        "Company" : "Google",
        "Product" : "Nexus",
        "No" : 1
}
{
        "_id" : ObjectId("53c639392eea8062e084cb58"),
        "Company" : "Apple",
        "Product" : "Mac",
        "No" : 2
}
{
        "_id" : ObjectId("53c63b26b003603dfdcf8c52"),
        "Company" : "Xiaomi",
        "Product" : "Mi3",
        "No" : 3
}
{
        "_id" : ObjectId("53c63bd1b003603dfdcf8c53"),
        "Product" : "Smart Watch",
        "No" : 4,
        "Company" : "Sony"
}

We have 4 documents in “names” collection.

remove() method, with simple condition

> db.names.remove({"No": 4});
WriteResult({ "nRemoved" : 1 })

> db.names.find().pretty()
{
        "_id" : ObjectId("53c6392a2eea8062e084cb57"),
        "Company" : "Google",
        "Product" : "Nexus",
        "No" : 1,
        "IT" : "true"
}
{
        "_id" : ObjectId("53c639392eea8062e084cb58"),
        "Company" : "Apple",
        "Product" : "Mac",
        "No" : 2,
        "IT" : "true"
}
{
        "_id" : ObjectId("53c63b26b003603dfdcf8c52"),
        "Company" : "Xiaomi",
        "Product" : "Mi3",
        "No" : 3,
        "IT" : "true"
}

Here the document with “No: 4” was removed from the collection.

Removing Documents: MongoDB

remove() method, with comparison condition

> db.names.remove({"No": {$gt: 2}});
WriteResult({ "nRemoved" : 1 })

> db.names.find().pretty()
{
        "_id" : ObjectId("53c6392a2eea8062e084cb57"),
        "Company" : "Google",
        "Product" : "Nexus",
        "No" : 1,
        "IT" : "true"
}
{
        "_id" : ObjectId("53c639392eea8062e084cb58"),
        "Company" : "Apple",
        "Product" : "Mac",
        "No" : 2,
        "IT" : "true"
}

Here whatever documents which has “No” greater than 2 got removed.

remove() method to remove all documents from the collection

> db.names.remove({});
WriteResult({ "nRemoved" : 2 })

> db.names.find().pretty()

> show collections
names
system.indexes

> db.system.indexes.find().pretty()
{ "v" : 1, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "test.names" }

If we pass empty argument to remove() method, it matches with all the documents present in the collection, hence removes all the documents one-by-one.

But it doesn’t remove the contents/documents/index present in “system.indexes” collection.

drop() method

> db.names.find()

> db.names.insert({"Company": "Apple", "Product": "iPhone", "No": 1});
WriteResult({ "nInserted" : 1 })

> db.names.insert({"Company": "Google", "Product": "Nexus", "No": 2});
WriteResult({ "nInserted" : 1 })

> db.names.find().pretty()
{
        "_id" : ObjectId("53c6c5d95879b1ff1f0b8356"),
        "Company" : "Apple",
        "Product" : "iPhone",
        "No" : 1
}
{
        "_id" : ObjectId("53c6392a2eea8062e084cb57"),
        "Company" : "Google",
        "Product" : "Nexus",
        "No" : 1,
        "IT" : "true"
}

> db.names.drop();
true

> db.names.find().pretty()

> db.system.indexes.find().pretty()

Since “names” collection was empty, we inserted 2 documents into it. Now we applied drop() method on the collection, which drops all the document present in the collections at once. It also removes the document/index/content present inside “system.indexes” collection.

Note: If you want to remove/drop all the documents present inside the collection, make use of drop() method, as it removes all the documents at once, its more efficient than remove({}) method which removes documents one by one. Use remove() method, when you want to remove one or a set of documents from the collection.