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Insert MongoDB document field only when it's missing?
Let us first create a collection with documents −
>db.missingDocumentDemo.insertOne({"StudentFirstName":"Adam","StudentLastName":"Smith"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd3fb1eedc6604c74817ce6")
}
>db.missingDocumentDemo.insertOne({"StudentFirstName":"Carol","StudentLastName":"Taylor"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd3fb29edc6604c74817ce7")
}
>db.missingDocumentDemo.insertOne({"StudentFirstName":"David","StudentLastName":"Miller","StudentAge":21});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd3fb40edc6604c74817ce8")
}Following is the query to display all documents from a collection with the help of find() method −
> db.missingDocumentDemo.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5cd3fb1eedc6604c74817ce6"),
"StudentFirstName" : "Adam",
"StudentLastName" : "Smith"
}
{
"_id" : ObjectId("5cd3fb29edc6604c74817ce7"),
"StudentFirstName" : "Carol",
"StudentLastName" : "Taylor"
}
{
"_id" : ObjectId("5cd3fb40edc6604c74817ce8"),
"StudentFirstName" : "David",
"StudentLastName" : "Miller",
"StudentAge" : 21
}Here is the query to insert MongoDB document field only when it's missing. We are trying to insert StudentAge field here. It won’t insert the field if it already exist −
> db.missingDocumentDemo.update(
... { "StudentAge": { "$exists": false } },
... { "$set": { "StudentAge": 23 } },
... { "multi": true }
... );
WriteResult({ "nMatched" : 2, "nUpserted" : 0, "nModified" : 2 })Let us display all the documents from the above collection −
> db.missingDocumentDemo.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5cd3fb1eedc6604c74817ce6"),
"StudentFirstName" : "Adam",
"StudentLastName" : "Smith",
"StudentAge" : 23
}
{
"_id" : ObjectId("5cd3fb29edc6604c74817ce7"),
"StudentFirstName" : "Carol",
"StudentLastName" : "Taylor",
"StudentAge" : 23
}
{
"_id" : ObjectId("5cd3fb40edc6604c74817ce8"),
"StudentFirstName" : "David",
"StudentLastName" : "Miller",
"StudentAge" : 21
}
Updated on: 30-Jul-2019
234 Views
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