MongoDB Field Update Operator - $unset
Description
In MongoDB, the $unset operator is used to delete a particular field. The value specified in the $unset expression does not make any impact on the operation. The $unset has no effect when the field does not exist in the document.
Syntax:
{ $unset: { <field1>: "", ... } }
Parameters:
Name | Description |
---|---|
field1 | name of the column or field to be deleted. |
Our database name is 'myinfo' and our collection name is "items1".
Sample collection "items1"
{ "_id" : 1, "description" : "item1", "op_stock" : 100, "purqty" : 100 }
Example of MongoDB $unset operator to delete field from first matching document
If we want to delete the purqty field from the document for _id is 1 the following mongodb command can be used-
>db.items1.update( { _id: 1 },{ $unset: {"purqty": ""}})
The above example will delete the field purqty from the document.
To see the newly inserted document -
> db.items1.find().pretty();
N.B. find() method displays the documents in a non structured format but to display the results in a formatted way, the pretty() method can be used.
Output of the command:
{ "_id" : 1, "description" : "item1", "op_stock" : 100 }
Example of MongoDB $unset operator to delete field from all matching documents
If we want to delete the specified field purqty from all the matching documents for the condition op_stock is greater than equal to 100, the following mongodb command can be used.
>db.items1.update({"op_stock":{$gte:100}}, { $unset: {"purqty": ""}},{ multi: true });
Here in the above example the "multi : true" have used to delete the specific field purqty from all the matching documents.
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