aggregate of _id

Understanding Aggregation of _id in MongoDB

Hello everyone, in this blog post, I will be explaining what the aggregation of _id means in MongoDB.

What is Aggregation in MongoDB?

MongoDB Aggregation is a process where data is searched, grouped, transformed, and returned in a customized format. It provides an alternative to the MapReduce method for processing data.

Aggregation Pipeline is a framework that allows you to aggregate and transform data in various stages. Aggregation of _id is one of the stages in the Aggregation Pipeline.

What is Aggregation of _id?

Aggregation of _id is a way to group and count the number of documents that share the same value for a specific field.

For example, suppose you have a collection of students with fields like name, age, and gender. If you want to count the number of students in each age group, you can use aggregation of _id.

The _id field is a special field in MongoDB that holds the value for the group by operation. You can use any valid expression as the _id field.

How to use Aggregation of _id in MongoDB?

To use Aggregation of _id in MongoDB, you need to use the $group operator in the aggregation pipeline.

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

In this example, we are grouping students by age and counting the number of students in each age group. The $sum operator is used to count the number of documents in each group.

You can also use Aggregation of _id to group documents based on multiple fields.

db.students.aggregate([
   {
      $group : {
         _id : {
            age: "$age",
            gender: "$gender"
         },
         count: { $sum: 1 }
      }
   }
])

In this example, we are grouping students by age and gender and counting the number of students in each group. The _id field is a document that contains two fields, age, and gender.

Conclusion

Aggregation of _id is a useful feature in MongoDB that allows you to group and count documents based on specific fields. It helps you to analyze your data and extract useful insights.

I hope this blog post has helped you understand what Aggregation of _id is and how to use it in MongoDB. If you have any questions or feedback, please feel free to leave a comment below.