C100DBA CRUD Operations Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  db.products.find({price: {$gt: 100}, category: 'electronics'})

  Why this is correct

  This query uses an implicit AND by specifying multiple field conditions in the query document. It matches documents where price is greater than 100 and category equals 'electronics'. This is the standard and most efficient way to combine conditions in MongoDB, as it uses the query optimizer effectively.

• ✗

  db.products.find({$or: [{price: {$gt: 100}}, {category: 'electronics'}]})

  Why it's wrong here

  This query uses $or, which would return documents that match either condition, not both. That would include products with price > 100 regardless of category, and products in 'electronics' regardless of price. This does not meet the requirement of both conditions being true simultaneously.

• ✗

  db.products.find({price: {$gt: 100}}).filter({category: 'electronics'})

  Why it's wrong here

  The find method does not have a .filter() method in MongoDB. This is not valid syntax. To filter results, you must include all conditions in the query document passed to find, or use aggregation. This option would result in an error.

• ✗

  db.products.find({$and: [{price: {$gt: 100}}, {category: 'electronics'}]})

  Why it's wrong here

  While this query is functionally correct and returns the same results, it is unnecessarily verbose. The $and operator is explicit and works, but the implicit AND is preferred for simplicity and readability. The question asks which query accomplishes the task; both A and B do, but only one is the best practice. However, since A is simpler and more common, it is the correct answer.