Query to fetch records where field is equal to particular value in MongoDB

Problem: Suppose we have to fetch records from a collection which one field is equal to particular value?

Solution: We can use $eq operator to fetch records from collection which one field has particular value. This is the comparison aggregation operator in mongodb.

• $eq returns true if values are equivalent.
• $eq returns false if values are not equivalent.

Syntax:

{ $eq: [ <expression1>, <expression2> ] }

Example: Suppose we have a collection of order which like following.

{ "_id" : 1, "item" : "item1", qty: 1, Price:500} { "_id" : 2, "item" : "item1", qty: 2, Price:200 } { "_id" : 3, "item" : "item1", qty: 4, Price:300 } { "_id" : 4, "item" : "item1", qty: 8, Price:700 } { "_id" : 5, "item" : "item1", qty: 2, Price:500 }

Run the following query

db.Order.aggregate(    [      {        $project:           {             item: 1,             Price: 1,             EqualResult: { $eq: [ "$Price", 200 ] },             _id: 0           }      }    ] )

Result:

{ "item" : "item1", "Price" : 500, "EqualResult" : false } { "item" : "item1", "Price" : 200, "EqualResult" : true } { "item" : "item1", "Price" : 300, "EqualResult" : false } { "item" : "item1", "Price" : 700, "EqualResult" : false } { "item" : "item1", "Price" : 500, "EqualResult" : false }

Example: From above collection if we want select those records which price value is equal to 200 and quantity is greater than 1.

Run the following query

db.Order.aggregate(      {$match: { $and: [{ Price: {$eq:200}}, { qty:{$gt:1}}] }} ) Or db.Order.aggregate(      {$match: { $and: [{ Price:200}, { qty:{$gt:1}}] }} ) Both are same.

Result:

{ "_id" : 2, "item" : "item1", "qty" : 2, "Price" : 200 }