POJO CRUD Operation Examples

Prerequisites

You must set up the following components to run the code examples in this guide:

• MongoDB server running on the default port for MongoDB (27017)

• Driver dependency installed in your project

• The following import statements:

  import com.mongodb.client.result.InsertOneResult;
  import com.mongodb.client.result.InsertManyResult;
  import com.mongodb.client.result.DeleteResult;
  import com.mongodb.client.result.UpdateResult;
  import com.mongodb.reactivestreams.client.MongoClient;
  import com.mongodb.reactivestreams.client.MongoClients;
  import com.mongodb.reactivestreams.client.MongoCollection;
  import com.mongodb.reactivestreams.client.MongoDatabase;
  import org.bson.codecs.configuration.CodecRegistry;
  import org.bson.codecs.pojo.PojoCodecProvider;
  import java.util.List;
  import static com.mongodb.client.model.Filters.*;
  import static com.mongodb.client.model.Updates.*;
  import static java.util.Arrays.asList;
  import static org.bson.codecs.configuration.CodecRegistries.fromProviders;
  import static org.bson.codecs.configuration.CodecRegistries.fromRegistries;

• POJO class definitions. Copy the full code for the Person and Address POJOs from the driver source repository on GitHub:

  • Person class

  • Address class

Creating a Custom CodecRegistry

Before you can use a POJO with the driver, you need to configure the CodecRegistry to include a codec that handles the translation to and from BSON for your POJOs. The simplest way to do that is to use the PojoCodecProvider.builder() method to create and configure a CodecProvider.

The following example combines the default codec registry with the PojoCodecProvider configured to automatically create POJO Codec instances:

CodecRegistry pojoCodecRegistry = fromRegistries(
    MongoClientSettings.getDefaultCodecRegistry(),
    fromProviders(PojoCodecProvider.builder().automatic(true).build())
);

Inserting a POJO into MongoDB

The codec registry automatically tries to create a POJO Codec for unknown classes. This allows you to use POJOs out of the box without any extra configuration.

Before you can insert a POJO into MongoDB, create a MongoCollection instance configured with the POJO class:

MongoCollection<Person> collection = database.getCollection("people", Person.class);

Person ada = new Person("Ada Byron", 20, new Address("St James Square", "London", "W1"));
collection.insertOne(ada).subscribe(new OperationSubscriber<InsertOneResult>());

List<Person> people = asList(
    new Person("Charles Babbage", 45, new Address("5 Devonshire Street", "London", "W11")),
    new Person("Alan Turing", 28, new Address("Bletchley Hall", "Bletchley Park", "MK12")),
    new Person("Timothy Berners-Lee", 61, new Address("Colehill", "Wimborne", null))
);
collection.insertMany(people).subscribe(new OperationSubscriber<InsertManyResult>());

Query the Collection

To query the collection, you can use the find() method.

The following example prints all the Person instances in the collection:

collection.find().subscribe(new PrintToStringSubscriber<>());

Person{id='...', name='Ada Byron', age=20, address=Address{street='St James Square', city='London', zip='W1'}}
Person{id='...', name='Charles Babbage', age=45, address=Address{street='5 Devonshire Street', city='London', zip='W11'}}
Person{id='...', name='Alan Turing', age=28, address=Address{street='Bletchley Hall', city='Bletchley Park', zip='MK12'}}
Person{id='...', name='Timothy Berners-Lee', age=61, address=Address{street='Colehill', city='Wimborne', zip='null'}}

Specify a Query Filter

To query for Person instances that match certain conditions, pass a filter object to the find() method. To facilitate creating filter objects, the driver provides Filters helper methods.

collection.find(eq("address.city", "Wimborne"))
    .first()
    .subscribe(new PrintToStringSubscriber<>());

Person{id='591dbc2550852fa685b3ad1a', name='Timothy Berners-Lee', age=61, address=Address{street='Colehill', city='Wimborne', zip='null'}}

collection.find(gt("age", 30)).subscribe(new PrintToStringSubscriber<>());

Update Documents

To update documents in a collection, you can use the collection's updateOne() and updateMany() methods.

Pass the following parameters to the methods:

• Filter object to determine the document or documents to update. To specify an empty filter and match all Person instances, use an empty Document object.

• Update document that specifies the modifications. To view a list of the available operators, see Update Operators in the Server manual.

The update methods return an UpdateResult type that provides information about the operation, including the number of documents modified by the update.

collection.updateOne(
    eq("name", "Ada Byron"),
    combine(set("age", 23), set("name", "Ada Lovelace"))
).subscribe(new OperationSubscriber<>());

collection.updateMany(not(eq("zip", null)), set("zip", null))
         .subscribe(new OperationSubscriber<>());

collection.replaceOne(eq("name", "Ada Lovelace"), ada)
    .subscribe(new OperationSubscriber<>());

Delete Documents

To delete documents from a collection, you can use the collection's deleteOne() and deleteMany() methods.

Pass a filter object to match the document or documents to delete. To specify an empty filter, use an empty Document object.

The delete methods return a DeleteResult type that provides information about the operation, including the number of documents deleted.

collection.deleteOne(eq("address.city", "Wimborne"))
    .subscribe(new OperationSubscriber<>());

collection.deleteMany(eq("address.city", "London"))
    .subscribe(new OperationSubscriber<>());