$match:

 In MongoDB shell (mongosh), the $match operator is used in the aggregate method to filter and select documents from a collection based on specified criteria. 

It allows you to include or exclude documents that match certain conditions.


Here's an explanation of how the $match operator works in MongoDB shell:


Syntax:

db.collection.aggregate([
  { $match: { <query> } }
])
  • db.collection :refers to the collection on which you want to perform the aggregation.

The aggregate method is used to execute an aggregation pipeline on the collection.

The $match stage is specified as an object within the aggregation pipeline.

<query> represents the criteria or conditions that documents must meet to be included in the result set.

 It uses MongoDB's query syntax.


Example:

Suppose you have a collection called "orders" that contains documents representing different orders placed by customers. Each document has fields like customerId, productId, and quantity.

 You want to retrieve all orders where the quantity is greater than or equal to 10.

db.orders.aggregate([
  {
    $match: { quantity: { $gte: 10 } }
  }
])

In the above example:


db.orders: refers to the "orders" collection.

The aggregate method is used to perform the aggregation operation.

The $match stage filters the documents based on the specified condition.

The { quantity: { $gte: 10 } } query specifies that only documents with a quantity field greater than or equal to 10 should be included in the result set.

The resulting output will contain only the orders where the quantity meets the specified condition.


The $match operator in MongoDB shell is an essential tool for filtering documents before performing further operations in the aggregation pipeline. 

It helps you narrow down the dataset based on specific criteria, improving query performance and allowing you to focus on the relevant documents for subsequent aggregation stages.