Which MongoDB questions to prepare for practice?

MongoDB Questions to Prepare for Practice

Practicing MongoDB questions helps in mastering its core concepts, query language, and real-world problem-solving skills. Below is a categorized list of questions for effective preparation.

1. Basic CRUD Operations

• How do you create a database and a collection in MongoDB?
• Write a query to insert one and multiple documents into a collection.

  db.collection.insertOne({ name: "Alice", age: 25 });
  db.collection.insertMany([{ name: "Bob" }, { name: "Charlie" }]);

• How do you retrieve all documents from a collection?
• Write a query to update a specific field in a document.

  db.collection.updateOne({ name: "Alice" }, { $set: { age: 26 } });

• How do you delete a document where a field matches a value?

2. Querying and Filtering

• Retrieve all documents where a field value matches a specific condition.

  db.collection.find({ age: { $gt: 25 } });

• How do you project specific fields in the result set?

  db.collection.find({}, { name: 1, age: 1 });

• Write a query using the $regex operator to find documents where a field starts with "A."
• How do you sort documents in ascending and descending order?

3. Aggregation Framework

• Write a query to group documents by a specific field and count the occurrences.

  db.collection.aggregate([{ $group: { _id: "$age", count: { $sum: 1 } } }]);

• Use the $match and $project stages in an aggregation pipeline.

  db.collection.aggregate([
    { $match: { age: { $gt: 25 } } },
    { $project: { name: 1, age: 1 } }
  ]);

• Perform an aggregation query to find the average age of users.

4. Indexing and Performance Optimization

• How do you create an index on a single field and multiple fields?

  db.collection.createIndex({ name: 1, age: -1 });

• How do you analyze the performance of a query using $explain?

  db.collection.find({ age: 25 }).explain("executionStats");

5. Advanced MongoDB Features

• How do you use MongoDB’s $lookup to perform a join between two collections?

  db.orders.aggregate([
    {
      $lookup: {
        from: "customers",
        localField: "customerId",
        foreignField: "_id",
        as: "customerDetails"
      }
    }
  ]);

• How do you implement a sharded cluster in MongoDB?
• Write a query to enable transactions and perform a multi-document update.

6. Real-World Scenarios

• Design a schema for an e-commerce platform in MongoDB.
• Write a query to find the top 3 most purchased products.

  db.orders.aggregate([
    { $unwind: "$products" },
    { $group: { _id: "$products", count: { $sum: 1 } } },
    { $sort: { count: -1 } },
    { $limit: 3 }
  ]);

• How would you store user activity logs efficiently in MongoDB?

7. Security and Administration

• How do you enable authentication in MongoDB?
• What is role-based access control (RBAC) in MongoDB, and how do you implement it?

Recommended Resources

• Grokking SQL for Tech Interviews: Strengthen your querying concepts. Check it out
• Grokking Relational Database Design and Modeling: Learn schema design and modeling for practical use cases. Explore here

By practicing these questions and exploring real-world scenarios, you'll be well-prepared for MongoDB interviews and practical applications.