Question

What does the mongoose popular method do, and what is the parameter of populate?

javascript
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Book.find({}).populate('x').exec(function (a, b) { (data); });
Option 1:
It populates the specified field in the result set with the corresponding document from another collection.

Option 2:
It removes the specified field from the result set.

Option 3:
It filters the result set based on the specified condition.

Option 4:
It performs a join operation with another collection.

Answer 1

The mongoose populate method replaces specified paths in a document with documents from another collection. Option 1 is correct, and Option 4 is partially correct as it resembles a join operation. Options 2 and 3 are incorrect regarding the populate method's functionality.

Step-by-step explanation:

The mongoose populate method is employed to automatically replace specified paths in the document with document(s) from other collection(s). In the code snippet provided, Book.find({}).populate('x'), the populate method is being used on the field 'x'. This indicates that the 'x' field is a reference to another collection, and mongoose will fetch the related document from that collection and include it in the result set. This process is similar to a join operation in SQL databases.

Given the options provided:

• Option 1 is correct: It populates the specified field in the result set with the corresponding document from another collection.
• Option 4 is somewhat correct as it is similar to a join operation. However, in the context of mongoose and MongoDB, the term used is 'populate' rather than 'join'.

Options 2 and 3 are incorrect with regard to what the populate method does.