MongoDB - collection

A MongoDB collection is a grouping of MongoDB documents. It is the equivalent of an RDBMS table. A collection exists within a single database and does not enforce a schema. In MongoDB, documents within a collection can have different fields and data types.

1. Dynamic Schema:

   • MongoDB is schema-less, meaning documents within a collection do not need to have the same structure. Each document can have different fields.

2. Creation:

   • Collections are created implicitly when the first document is inserted. MongoDB creates a collection dynamically as soon as data is inserted into it.

3. Accessing Collections:

   • In the MongoDB shell, you can access a collection using the db.collection_name notation. For example, db.users refers to the "users" collection.

4. Inserting Documents:

   • You can insert documents into a collection using the insertOne or insertMany methods.

     db.collection_name.insertOne({ field1: value1, field2: value2 });

5. Querying Documents:

   • The find method is used to query documents in a collection. It returns a cursor to the documents that match the query criteria.

     db.collection_name.find({ field: value });

6. Updating Documents:

   • You can update documents in a collection using the updateOne or updateMany methods.

     db.collection_name.updateOne({ field: value }, { $set: { updated_field: new_value } });

7. Deleting Documents:

   • Documents can be deleted using the deleteOne or deleteMany methods.

     db.collection_name.deleteOne({ field: value });

8. Indexing:

   • Indexes can be created on fields to improve query performance.

     db.collection_name.createIndex({ field: 1 });

9. Aggregation:

   • MongoDB supports aggregation pipelines for complex data transformations.

     db.collection_name.aggregate([
       { $group: { _id: "$field", count: { $sum: 1 } } }
     ]);