Multi-Update: MongoDB

Lets learn how to update all the documents present in a collection using update() method, using the option multi: true

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.

find() method

> db.names.find({}, {"Company": 1, "_id": 0}).pretty()
{ "Company" : "Google" }
{ "Company" : "Apple" }
{ "Company" : "Xiaomi" }
{ "Company" : "Sony" }

If we leave the first argument of find() method empty, it matches with all the documents of the collection. Hence it fetched all the Company names from the documents.

Multi-Update: MongoDB

update() method

> db.names.update({}, {$set: {"IT": "true"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 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
}
{
        "_id" : ObjectId("53c63b26b003603dfdcf8c52"),
        "Company" : "Xiaomi",
        "Product" : "Mi3",
        "No" : 3
}
{
        "_id" : ObjectId("53c63bd1b003603dfdcf8c53"),
        "Product" : "Smart Watch",
        "No" : 4,
        "Company" : "Sony"
}

But in case of update() method, if the first argument is left empty, it randomly matches to only 1 document in the collection.

Related Read: Update with SET Operator: MongoDB

unset the IT field

> db.names.update({"IT": {$exists: true}}, {$unset: {"IT": "true"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

> 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"
}

Here we select the document which has a field called “IT” and remove it from that document.

Related Read:
$exists, $type, $regex operators: MongoDB
Update with UNSET Operator: MongoDB

multi-update true

> db.names.update({}, {$set: {"IT": "true"}}, {multi: true});
WriteResult({ "nMatched" : 4, "nUpserted" : 0, "nModified" : 4 })

> 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"
}
{
        "_id" : ObjectId("53c63bd1b003603dfdcf8c53"),
        "Product" : "Smart Watch",
        "No" : 4,
        "Company" : "Sony",
        "IT" : "true"
}

Here we have 3 arguments for update() method. First one is intentionally left empty. In second argument, we specify the changes needed to the documents. In third argument we specify the option, multi: true – which tells mongo engine to match with all the documents in the collection.