mongodb aggregation

Aggregation in MongoDB is a way to process data and perform calculations on it to generate meaningful results. The MongoDB aggregation framework provides a set of operators to perform data aggregation, such as grouping, sorting, filtering, and transforming data.

Here is an example of how to use the aggregation framework in MongoDB to group documents in a collection by a specified field and calculate the count of documents in each group:

db.mycollection.aggregate([
  { $group: { _id: "$field1", count: { $sum: 1 } } }
])

In this example, the aggregate() method is used to perform aggregation on the "mycollection" collection. The $group operator is used to group the documents in the collection by the "field1" field, and the $sum operator is used to calculate the count of documents in each group.

You can also use the aggregation framework to perform other types of aggregation, such as sorting and filtering data. For example, to sort the documents in a collection named "mycollection" by the "field1" field in ascending order and return only the first 10 documents, you can use the following aggregation pipeline:

db.mycollection.aggregate([
  { $sort: { field1: 1 } },
  { $limit: 10 }
])

In this example, the $sort operator is used to sort the documents in the collection by the "field1" field in ascending order, and the $limit operator is used to limit the result to the first 10 documents.