MongoDB – $eq Operator
MongoDB $eq operator or equality operator is a comparison operator. The $eq operator matches documents where the value of the field is equal to the specified value.
Important Points:
- If the given value is a document, then the order of the fields in the document is important.
- If the given value is an array, then MongoDB matches the documents where the field contains an element that exactly matches the specified array.
Syntax
{field: {$eq: value}}
or
{field: value}
MongoDB $eq Operator Example
In the following examples, we are working with:
Database: w3wiki
Collection: employee
Document: five documents that contain the details of the employees in the form of field-value pairs.
Example 1
In this example, we are selecting those documents where the value of the salary field is equal to 30000.
Query
db.employee.find({salary: {$eq: 30000}}).pretty()
You can also use the syntax:
db.employee.find({salary: 30000}).pretty()
Output
Example 2
In this example, we are selecting those documents where the first name of the employee is equal to Amu. We are specifying conditions on the field in the embedded document using dot notation in this example.
Query
db.employee.find({"name.first": {$eq: "Amu"}}).pretty()
Or, you can also write the query as
db.employee.find({"name.first": "Amu"}).pretty()
Output:
Example 3
In this example, we are selecting those documents where the language array contains an element with value “C++”.
Query
db.employee.find({language: {$eq: "C++"}}).pretty()
Or, you can also write the query as
db.employee.find({language: "C++"}).pretty()
Output:
Example 4
In this example, we are selecting those documents where the language array is equal to the specified array.
Query
db.employee.find({language: {$in: ["C#", "Java"]}}).pretty()
Or, you can also write the query as:
db.employee.find({language: {$all: ["C#", "Java"]}}).pretty()
Output:
Key Takeaways About $eq Operator
- The $eq Operator is one of the comparison operator in MongoDB.
- It is used to match values exactly in MongoDB.
- It is used to filter data based on exact match.
- If the specified
<value>
is an array, MongoDB matches documents where the<field>
matches the array exactly or the<field>
contains an element that matches the array exactly.
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