example code for BAEL-1961 (#5781)

* added example code for BAEL-2366

* moved example code for BAEL-2366

* example code for BAEL-1961

* moved example code into integration test

* updated the test assertions

spring-boot/src/main/java/com/baeldung/mongodb/Application.java

@@ -1,11 +1,19 @@
 package com.baeldung.mongodb;
 
+import com.baeldung.mongodb.daos.UserRepository;
+import com.baeldung.mongodb.models.User;
+import org.springframework.boot.CommandLineRunner;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
+
+import java.util.List;
 
 @SpringBootApplication
 public class Application {
+
     public static void main(String[] args) {
         SpringApplication.run(Application.class, args);
     }
+
 }

spring-boot/src/main/java/com/baeldung/mongodb/daos/UserRepository.java

@@ -0,0 +1,10 @@
+package com.baeldung.mongodb.daos;
+
+
+import com.baeldung.mongodb.models.User;
+import org.springframework.data.mongodb.repository.MongoRepository;
+
+
+public interface UserRepository extends MongoRepository<User, Long> {
+
+}

spring-boot/src/main/java/com/baeldung/mongodb/events/UserModelListener.java

@@ -0,0 +1,28 @@
+package com.baeldung.mongodb.events;
+
+
+import com.baeldung.mongodb.models.User;
+import com.baeldung.mongodb.services.SequenceGeneratorService;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.mongodb.core.mapping.event.AbstractMongoEventListener;
+import org.springframework.data.mongodb.core.mapping.event.BeforeConvertEvent;
+import org.springframework.stereotype.Component;
+
+
+@Component
+public class UserModelListener extends AbstractMongoEventListener<User> {
+
+    private SequenceGeneratorService sequenceGenerator;
+
+    @Autowired
+    public UserModelListener(SequenceGeneratorService sequenceGenerator) {
+        this.sequenceGenerator = sequenceGenerator;
+    }
+
+    @Override
+    public void onBeforeConvert(BeforeConvertEvent<User> event) {
+        event.getSource().setId(sequenceGenerator.generateSequence(User.SEQUENCE_NAME));
+    }
+
+
+}

spring-boot/src/main/java/com/baeldung/mongodb/models/DatabaseSequence.java

@@ -0,0 +1,32 @@
+package com.baeldung.mongodb.models;
+
+import org.springframework.data.annotation.Id;
+import org.springframework.data.mongodb.core.mapping.Document;
+
+
+@Document(collection = "database_sequences")
+public class DatabaseSequence {
+
+    @Id
+    private String id;
+
+    private long seq;
+
+    public DatabaseSequence() {}
+
+    public String getId() {
+        return id;
+    }
+
+    public void setId(String id) {
+        this.id = id;
+    }
+
+    public long getSeq() {
+        return seq;
+    }
+
+    public void setSeq(long seq) {
+        this.seq = seq;
+    }
+}

spring-boot/src/main/java/com/baeldung/mongodb/models/User.java

@@ -0,0 +1,73 @@
+package com.baeldung.mongodb.models;
+
+import org.springframework.data.annotation.Id;
+import org.springframework.data.annotation.Transient;
+import org.springframework.data.mongodb.core.mapping.Document;
+
+
+@Document(collection = "users")
+public class User {
+
+    @Transient
+    public static final String SEQUENCE_NAME = "users_sequence";
+
+    @Id
+    private long id;
+
+    private String firstName;
+
+    private String lastName;
+
+    private String email;
+
+    public User() { }
+
+    public User(String firstName, String lastName, String email) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+        this.email = email;
+    }
+
+    public long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+    
+
+    @Override
+    public String toString() {
+        return "User{" +
+                "id=" + id +
+                ", firstName='" + firstName + '\'' +
+                ", lastName='" + lastName + '\'' +
+                ", email='" + email + '\'' +
+                '}';
+    }
+}

spring-boot/src/main/java/com/baeldung/mongodb/services/SequenceGeneratorService.java

@@ -0,0 +1,35 @@
+package com.baeldung.mongodb.services;
+
+import com.baeldung.mongodb.models.DatabaseSequence;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.mongodb.core.MongoOperations;
+import org.springframework.data.mongodb.core.query.Update;
+import org.springframework.stereotype.Service;
+
+import java.util.Objects;
+
+import static org.springframework.data.mongodb.core.FindAndModifyOptions.options;
+import static org.springframework.data.mongodb.core.query.Criteria.where;
+import static org.springframework.data.mongodb.core.query.Query.query;
+
+
+@Service
+public class SequenceGeneratorService {
+
+
+    private MongoOperations mongoOperations;
+
+    @Autowired
+    public SequenceGeneratorService(MongoOperations mongoOperations) {
+        this.mongoOperations = mongoOperations;
+    }
+
+    public long generateSequence(String seqName) {
+
+        DatabaseSequence counter = mongoOperations.findAndModify(query(where("_id").is(seqName)),
+                new Update().inc("seq",1), options().returnNew(true).upsert(true),
+                DatabaseSequence.class);
+        return !Objects.isNull(counter) ? counter.getSeq() : 1;
+
+    }
+}

spring-boot/src/test/java/com/baeldung/mongodb/MongoDbAutoGeneratedFieldIntegrationTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.mongodb;
+
+import com.baeldung.mongodb.daos.UserRepository;
+import com.baeldung.mongodb.models.User;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.junit4.SpringRunner;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+
+
+@RunWith(SpringRunner.class)
+public class MongoDbAutoGeneratedFieldIntegrationTest {
+
+    @Autowired
+    private UserRepository userRepository;
+
+    @Test
+    public void contextLoads() {}
+
+    @Test
+    public void givenUserObject_whenSave_thenCreateNewUser() {
+
+        User user = new User();
+        user.setFirstName("John");
+        user.setLastName("Doe");
+        user.setEmail("john.doe@example.com");
+        userRepository.save(user);
+
+        assertThat(userRepository.findAll().size()).isGreaterThan(0);
+    }
+
+
+}