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mongodb query using conditional operator $size

MongoDB Field Update Operator - $inc

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Description

In MongoDB, the $inc operator is used to increment the value of a field by a specified amount. The $inc operator adds as a new field when the specified field does not exist, and sets the field to the specified amount. The $inc accepts positive and negative value as an incremental amount.

Syntax

{ $inc: { <field1>: <amount1>, ... } }

Parameters

Name Description
field1 name of the column or field
amount1 incremental value

Our database name is 'myinfo' and our collection name is "items". Here, is the collection bellow.

Sample collection "items"

{
        "_id" : 1,
        "item_id" : "I001",
        "comp_id" : "C001",
        "qty" : 25,
        "prate" : 30,
        "srate" : 35,
        "mrp" : 40
}
{
        "_id" : 2,
        "item_id" : "I001",
        "comp_id" : "C002",
        "qty" : 30,
        "prate" : 32,
        "srate" : 37,
        "mrp" : 40
}

Example of field update operator - $inc

If we want to increment the value of qty by 10 for the first matching document in the collection items for item_id is I001 the following mongodb statement can be used:

> db.items.update( { item_id: "I001" },{ $inc: { qty: 10 }});

Here in the above example-

  • The qty for the first matching document for the condition item_id is I001 have been updated and the qty became 35 from 25 and the rest remains same.

To see the updated output -

> db.items.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,
        "item_id" : "I001",
        "comp_id" : "C001",
        "qty" : 35,
        "prate" : 30,
        "srate" : 35,
        "mrp" : 40
}
{
        "_id" : 2,
        "item_id" : "I001",
        "comp_id" : "C002",
        "qty" : 30,
        "prate" : 32,
        "srate" : 37,
        "mrp" : 40
}

Example of $inc operator with multi:true

If we want to add a new field like tax% with a specific value 2 for all the documents in the collection items for item_id is I001, following mongodb queries can be used -

> db.items.update( { "item_id": "I001" }, { $inc: { "tax%": 2 } }, { multi: true } );

Here in the above example-

  • A new field tax% which does not exists have been added with a value of 2 for all documents which match the condition item_id is I001. Here "multi : true" have used to update all documents which matching the specified condition.

To see the updated output -

> db.items.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,
        "comp_id" : "C001",
        "item_id" : "I001",
        "mrp" : 40,
        "prate" : 30,
        "qty" : 35,
        "srate" : 35,
        "tax%" : 2
}
{
        "_id" : 2,
        "comp_id" : "C002",
        "item_id" : "I001",
        "mrp" : 40,
        "prate" : 32,
        "qty" : 30,
        "srate" : 37,
        "tax%" : 2
}

Example of $inc operator on multiple fields

If we want to increment the tax% and mrp for all the matching documents against a condition the following mongodb command can be used -

> db.items.update( { "item_id": "I001" }, { $inc: { "tax%": 2,"mrp":-2 } }, { multi: true } );

Here in the above example-

  • the $inc operator expression specifies 2 for tax% and -2 for mrp field to increase the value of tax% by 2 and decrease the mrp by 2 simultaneously. The "multi : true" have used to update all matching documents for the specified condition.

To see the updated output -

> db.items.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,
        "comp_id" : "C001",
        "item_id" : "I001",
        "mrp" : 38,
        "prate" : 30,
        "qty" : 35,
        "srate" : 35,
        "tax%" : 4
}
{
        "_id" : 2,
        "comp_id" : "C002",
        "item_id" : "I001",
        "mrp" : 38,
        "prate" : 32,
        "qty" : 30,
        "srate" : 37,
        "tax%" : 4
}


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