The project demonstrates basic CRUD examples using MongoDB and SpringBoot

For this tutorial, we need to create a Spring Boot project, which can be done easily using Spring Initialzr. It is advantageous to use an IDE (Integrated Development Environment) like Eclipse for this tutorial.

Project Setup

Once the project is setup, we need to create Java class and fields that will be mapped into MongoDB collection and fields.

For the API implementation, we use two approaches:

MongoRepository - We demonstrate all the CRUD operations using this approach.
MongoTemplate - It is used for more control over filters, and also a good choice for aggregations. We will demonstrate update operation using this approach.

CRUD Examples using MongoRepository

To create a document (item) in MongoDB, use the save() method:

groceryItemRepo.save(new GroceryItem("Dried Red Chilli", "Dried Whole Red Chilli", 2, "spices"));

To Read all the documents, use findAll() method:

groceryItemRepo.findAll().forEach(item-> item.getName(),item.getQuantity(),item.getCategory());

To Read documents based on a particular field, like name or category, by specifying the query parameters:

@Query("{name:'?0'}")
GroceryItem findItemByName(String name);

@Query(value="{category:'?0'}", fields="{'name' : 1, 'quantity' : 1}")
List<GroceryItem> findAll(String category);

To update a document using MongoRepository, we should retrieve the specific documents and save the new values. For example, to update a category, do the following:

List<GroceryItem> list = groceryItemRepo.findAll(category);
	 
list.forEach(item -> {
   // Update the category in each document
	 item.setCategory(newCategory);
});
	 
// Save all the items in database
List<GroceryItem> itemsUpdated = groceryItemRepo.saveAll(list);

To delete a document, use the delete method. For example, delete an item by ID using the deleteById() method:

groceryItemRepo.deleteById(id);

Update using MongoTemplate

Updates using MongoTemplate are much easier with the out-of-box classes provided by MongoTemplate. Let us update the quantity of a particular item:

Query query = new Query(Criteria.where("name").is(name));
Update update = new Update();
update.set("quantity", newQuantity);		
UpdateResult result = mongoTemplate.updateFirst(query, update, GroceryItem.class);