Lets use $set operator along with update() method, to update the documents.
test database, names collection
1 2 3 | > db.names.find()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "name" : "Alia" }
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" } |
Related Read: Update Method: MongoDB
Lets update the first document using only update method.
1 2 3 4 5 6 7 8 9 10 | > db.names.update({"name": "Alia"}, {"name": "Alia", "age": 25});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{
"_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"),
"name" : "Alia",
"age" : 25
} |
Everything is ok in this case. But what if you forget to mention the name field in the second argument of update() method.
1 2 3 4 5 6 | > db.names.update({"name": "Alia"}, {"age": 25});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"), "name" : "Bebo" }
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "age" : 25 } |
In this case, the name field gets erased. As we did not specify name field in the second parameter of update() method.
Using $set operator
1 2 3 4 5 6 7 8 9 10 | > db.names.update({"name": "Bebo"}, {$set: {"age": 25}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "age" : 25 }
{
"_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"),
"name" : "Bebo",
"age" : 25
} |
Here we make use of document with name as Bebo. Using $set operator we only specify the fields we want to add or update. Need not specify other existing fields in order to retain them.
Update with SET Operator: MongoDB
[youtube https://www.youtube.com/watch?v=nsDnZcstUV4]
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | > db.names.update({"name": "Bebo"}, {$set: {"age": 25, "salary": 25}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "age" : 25 }
{
"_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"),
"name" : "Bebo",
"age" : 25,
"salary" : 25
}
> db.names.update({"name": "Bebo"}, {$set: {"age": 26, "salary": 25}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "age" : 25 }
{
"_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"),
"name" : "Bebo",
"age" : 26,
"salary" : 25
}
> db.names.update({"name": "Bebo"}, {$set: {"salary": 30}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.names.find().pretty()
{ "_id" : ObjectId("53be5d4604cc1cb0a7bfc3c0"), "age" : 25 }
{
"_id" : ObjectId("53be5d5204cc1cb0a7bfc3c1"),
"name" : "Bebo",
"age" : 26,
"salary" : 30
} |
We can update existing field or add a field to the existing document using $set operator and need not to worry about the other fields in the document.