Recall & Review
beginner
What is the purpose of the MongoDB aggregation pipeline?
The aggregation pipeline processes data in stages, transforming documents step-by-step to produce aggregated results.
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beginner
Name the first stage in a MongoDB aggregation pipeline and its role.
The $match stage filters documents to pass only those that meet specified criteria to the next stage.
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intermediate
How does data flow through the stages in a MongoDB pipeline?
Data flows sequentially from one stage to the next, with each stage receiving input from the previous and outputting transformed data.
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intermediate
What happens if a stage in the pipeline changes the shape of documents?
The next stage receives documents in the new shape, so each stage can build on transformations made earlier.
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intermediate
Why is the order of stages important in a MongoDB aggregation pipeline?
Because each stage depends on the output of the previous one, changing the order can change the final result or cause errors.
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What does the $group stage do in a MongoDB pipeline?
✗ Incorrect
The $group stage groups documents by a key and performs aggregation like sum or average.
Which stage should come first to reduce data early in the pipeline?
✗ Incorrect
The $match stage filters documents early to reduce the amount of data processed in later stages.
If you want to add a new field to documents, which stage do you use?
✗ Incorrect
$addFields adds new fields or modifies existing ones in documents.
What happens if you place $sort after $limit in a pipeline?
✗ Incorrect
Placing $sort after $limit sorts only the limited subset of documents.
Which stage reshapes documents to include only specified fields?
✗ Incorrect
$project controls which fields to include or exclude in the output documents.
Explain how data flows through the stages in a MongoDB aggregation pipeline.
Think of it like an assembly line where each step changes the product a bit.
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Why is the order of stages important in a MongoDB pipeline? Give an example.
Consider filtering data early to improve performance.
You got /3 concepts.