Which Mongodb coding interview questions to prepare?

MongoDB Coding Interview Questions to Prepare

Preparing for MongoDB coding interviews involves focusing on fundamental operations, advanced queries, and real-world problem-solving scenarios. Below is a list of commonly asked MongoDB coding interview questions, categorized for effective preparation.

1. Basic CRUD Operations

• Write a query to insert a single document and multiple documents into a collection.

  db.collection.insertOne({ name: "Alice", age: 30 });
  db.collection.insertMany([{ name: "Bob" }, { name: "Charlie" }]);

• How do you retrieve documents where a field meets a specific condition?

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

• Write a query to update a specific field in a document.

  db.collection.updateOne({ name: "Alice" }, { $set: { age: 31 } });

• How do you delete a document from a collection?

  db.collection.deleteOne({ name: "Bob" });

2. Advanced Queries

• Retrieve all documents where a field contains a value in an array.

  db.collection.find({ hobbies: { $in: ["reading", "swimming"] } });

• Use the $regex operator to find documents where a field matches a pattern.

  db.collection.find({ name: { $regex: "^A", $options: "i" } });

• Perform a query to retrieve only specific fields of documents.

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

3. Aggregation Framework

• Group documents by a specific field and calculate counts.

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

• Use $match and $project stages to filter and reshape data.

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

• Sort documents in descending order using the $sort stage.

  db.collection.aggregate([{ $sort: { age: -1 } }]);

4. Indexing and Optimization

• Create an index on a field to optimize query performance.

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

• How do you analyze a query's performance using $explain?

  db.collection.find({ age: 30 }).explain("executionStats");

5. Real-World Scenarios

• Design a query to fetch all orders placed by a user within the last 30 days.

  db.orders.find({
    userId: "12345",
    orderDate: { $gte: new Date(new Date() - 30 * 24 * 60 * 60 * 1000) }
  });

• How would you handle a many-to-many relationship in MongoDB?

• Write a query to find the top 5 most frequently purchased products.

  db.orders.aggregate([
    { $unwind: "$products" },
    { $group: { _id: "$products", count: { $sum: 1 } } },
    { $sort: { count: -1 } },
    { $limit: 5 }
  ]);

Recommended Resources

To master MongoDB coding questions:

• Grokking the Coding Interview: Patterns for Coding Questions: Build foundational problem-solving skills. Explore the course
• Grokking SQL for Tech Interviews: Learn querying concepts that apply to both SQL and NoSQL databases. Check it out

These questions and resources will help you confidently tackle MongoDB coding interview challenges.