Lets use $unset operator along with update() method, to update the documents.
test database, names collection
1 2 3 4 5 6 7 8 9 10 11 12 13 | > db.names.find().pretty()
{
"_id" : ObjectId("53c3fc2005e0ce2719d91bd2"),
"Company" : "Google",
"Product" : "Nexus",
"No" : 1
}
{
"_id" : ObjectId("53c3fd3bb9ae26fa217b1e12"),
"Company" : "Apple",
"Product" : "iPhone",
"No" : 2
} |
Here we have 2 documents with fields _id, Company, Product and No.
Update with UNSET Operator: MongoDB
[youtube https://www.youtube.com/watch?v=8UUdITiZ5ZE]
We could remove a field using update() method, by not specifying it in the second argument.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | > db.names.update({"No": 1}, {"Company": "Google", "No": 1});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{
"_id" : ObjectId("53c3fc2005e0ce2719d91bd2"),
"Company" : "Google",
"No" : 1
}
{
"_id" : ObjectId("53c3fd3bb9ae26fa217b1e12"),
"Company" : "Apple",
"Product" : "iPhone",
"No" : 2
} |
Related Read: Update Method: MongoDB
This way, we could eliminate the field Product. But this is a tedious process – we need to remember all the fields inorder to achieve this. It gets difficult when we have many fields in our document. To solve this problem, we have $unset operator, where we only need to know the field name which we want to remove.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | > db.names.update({"No": 1}, {$unset: {"Product": 1}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{
"_id" : ObjectId("53c3fc2005e0ce2719d91bd2"),
"Company" : "Google",
"No" : 1
}
{
"_id" : ObjectId("53c3fd3bb9ae26fa217b1e12"),
"Company" : "Apple",
"Product" : "iPhone",
"No" : 2
} |
$unset operator syntax is same to unset or remove array from a document.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 | > db.names.update({"No": 1}, {$set: {"Product": ["LG", "Samsung", "HTC"]}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{
"_id" : ObjectId("53c3fc2005e0ce2719d91bd2"),
"Company" : "Google",
"No" : 1,
"Product" : [
"LG",
"Samsung",
"HTC"
]
}
{
"_id" : ObjectId("53c3fd3bb9ae26fa217b1e12"),
"Company" : "Apple",
"Product" : "iPhone",
"No" : 2
}
> db.names.update({"No": 1}, {$unset: {"Product": 1}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{
"_id" : ObjectId("53c3fc2005e0ce2719d91bd2"),
"Company" : "Google",
"No" : 1
}
{
"_id" : ObjectId("53c3fd3bb9ae26fa217b1e12"),
"Company" : "Apple",
"Product" : "iPhone",
"No" : 2
} |
Related Read: Update with SET Operator: MongoDB