MongoDB query to set user defined variable into query?

To set user-defined variables in MongoDB queries, use the var keyword to declare variables and reference them directly in your query conditions.

Syntax

var variableName = "value";
db.collection.find({"fieldName": variableName});

Sample Data

db.demo327.insertMany([
    {"FirstName": "Chris", "LastName": "Brown"},
    {"FirstName": "David", "LastName": "Miller"},
    {"FirstName": "John", "LastName": "Doe"},
    {"FirstName": "John", "LastName": "Smith"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e516952f8647eb59e562076"),
        ObjectId("5e51695af8647eb59e562077"),
        ObjectId("5e516962f8647eb59e562078"),
        ObjectId("5e516968f8647eb59e562079")
    ]
}

Example: Using Variable in Query

First, verify the sample data ?

db.demo327.find();

{ "_id": ObjectId("5e516952f8647eb59e562076"), "FirstName": "Chris", "LastName": "Brown" }
{ "_id": ObjectId("5e51695af8647eb59e562077"), "FirstName": "David", "LastName": "Miller" }
{ "_id": ObjectId("5e516962f8647eb59e562078"), "FirstName": "John", "LastName": "Doe" }
{ "_id": ObjectId("5e516968f8647eb59e562079"), "FirstName": "John", "LastName": "Smith" }

Now define a variable and use it in the query ?

var name = "John";
db.demo327.find({"FirstName": name});

{ "_id": ObjectId("5e516962f8647eb59e562078"), "FirstName": "John", "LastName": "Doe" }
{ "_id": ObjectId("5e516968f8647eb59e562079"), "FirstName": "John", "LastName": "Smith" }

Key Points

• Variables are declared using var variableName = value; syntax.
• Reference variables directly in query conditions without quotes.
• Variables can store strings, numbers, arrays, or objects for reuse in queries.

Conclusion

User-defined variables in MongoDB provide a convenient way to store values and reuse them across multiple queries. Simply declare with var and reference the variable name in your query conditions.