MEAN MongoDB Advanced Operations

Question 1

Which MongoDB aggregation stage is used to filter documents before passing them to the next stage in the pipeline?

Accepted Answer

$match

Answer

The $match stage filters documents using query conditions, similar to find(), and should be placed early in the pipeline for performance.

Question 2

What does the $lookup aggregation stage do in MongoDB?

Accepted Answer

Performs a left outer join with another collection

Answer

$lookup performs a left outer join between two collections in the same database, adding matched documents as an array field.

Question 3

Which MongoDB index type is best suited for geospatial queries?

Accepted Answer

2dsphere

Answer

A 2dsphere index supports queries on GeoJSON objects and legacy coordinate pairs for geospatial calculations.

Question 4

What is the purpose of the MongoDB `explain()` method?

Accepted Answer

Returns execution plan and performance statistics for a query

Answer

explain() provides details about query execution, including the winning plan, index usage, and statistics like documents examined.

Question 5

In MongoDB, what does a 'covered query' mean?

Accepted Answer

A query satisfied entirely by an index without accessing documents

Answer

A covered query is one where all fields in the query and projection are part of the index, so MongoDB never needs to read the actual documents.

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