MongoTemplate and MongoRepository

MongoTemplate and MongoRepository are both part of Spring Data MongoDB, but they serve different purposes and offer different levels of abstraction for interacting with MongoDB. Here’s a detailed comparison to help you understand when to use each:

MongoTemplate

MongoTemplate provides a low-level, flexible, and comprehensive way to interact with MongoDB. You can use it for any kind of MongoDB operations, including custom queries, updates, and aggregations.

Key Features:

1. Flexibility: Allows for complex queries and custom operations.
2. Aggregation Support: Provides comprehensive support for MongoDB aggregation framework.
3. CRUD Operations: Supports basic create, read, update, and delete operations.
4. Bulk Operations: Allows for performing bulk operations.
5. Transactions: Supports MongoDB transactions where applicable.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.stereotype.Service;

@Service
public class MyService {

    @Autowired
    private MongoTemplate mongoTemplate;

    public void saveMyObject(MyObject obj) {
        mongoTemplate.save(obj);
    }

    public MyObject findMyObjectById(String id) {
        return mongoTemplate.findById(id, MyObject.class);
    }

    public List<MyObject> findMyObjectsByField(String fieldValue) {
        Query query = new Query(Criteria.where("myField").is(fieldValue));
        return mongoTemplate.find(query, MyObject.class);
    }
}

MongoRepository

MongoRepository is part of Spring Data’s repository abstraction, which provides a higher-level, easier-to-use approach compared to MongoTemplate. MongoRepository uses convention over configuration, meaning it provides basic CRUD operations out of the box and derives query methods from method names.

Key Features:

1. Simplicity: Provides a simple and easy-to-use interface for basic CRUD operations.
2. Query Derivation: Automatically derives query methods from method names.
3. Pagination and Sorting: Built-in support for pagination and sorting.
4. Custom Queries: Supports custom query methods using the @Query annotation.
5. Integration with Spring Data: Seamless integration with other Spring Data modules.

import org.springframework.data.mongodb.repository.MongoRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface MyRepository extends MongoRepository<MyObject, String> {
    // Derived query method
    List<MyObject> findByMyField(String fieldValue);

    // Custom query method
    @Query("{ 'myField' : ?0 }")
    List<MyObject> findCustomByMyField(String fieldValue);
}

Service Layer Using MongoRepository:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class MyService {

    @Autowired
    private MyRepository myRepository;

    public void saveMyObject(MyObject obj) {
        myRepository.save(obj);
    }

    public MyObject findMyObjectById(String id) {
        return myRepository.findById(id).orElse(null);
    }

    public List<MyObject> findMyObjectsByField(String fieldValue) {
        return myRepository.findByMyField(fieldValue);
    }
}

When to Use What?

Use MongoTemplate:

1. When you need fine-grained control over MongoDB operations.
2. When you need to perform complex queries or aggregations.
3. When you need to perform custom updates or bulk operations.
4. When you need more flexibility in handling MongoDB transactions.

Use MongoRepository:

1. When you prefer simplicity and convention over configuration.
2. When you need basic CRUD operations with minimal boilerplate code.
3. When you want to leverage Spring Data’s repository abstraction for automatic query derivation.
4. When you need built-in support for pagination and sorting.

In summary, MongoRepository is suitable for simple CRUD operations and straightforward query derivation, making it easy to get started and maintain. On the other hand, MongoTemplate provides the flexibility and power needed for more complex operations, custom queries, and advanced use cases.