In this tutorial, we will show you how to generate an auto-incrementing sequence id in MongoDB + Spring Data environment.

Tools used in this project :

1. Spring Data MongoDB 1.2.1.RELEASE
2. MongoDB 2.4.5
3. Eclipse 4.2
4. Maven 3

At the end of this tutorial, if the collection name “hosting” is saved, a new auto-incrementing sequence id will be assigned. Below is the Java code snippet to generate the sequence id.

  public long getNextSequenceId(String key) {
	Query query = new Query(Criteria.where("_id").is(key));
        Update update = new Update();
	update.inc("seq", 1);
	FindAndModifyOptions options = new FindAndModifyOptions();
	options.returnNew(true);
	SequenceId seqId = 
            mongoOperation.findAndModify(query, update, options, SequenceId.class);
	return seqId.getSeq();
  }	

1. Project Structure

Review the project directory structure, a standard Maven project.

2. Maven Pom

In case you are interested at the project dependencies.

<project ...>
	<properties>
		<jdk.version>1.6</jdk.version>
		<spring.version>3.2.2.RELEASE</spring.version>
		<mongojavadriver.version>2.11.1</mongojavadriver.version>
		<springdata.version>1.2.1.RELEASE</springdata.version>
	</properties>
	<dependencies>
		<!-- Spring Core -->
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-core</artifactId>
			<version>${spring.version}</version>
		</dependency>
		<!-- need this for @Configuration -->
		<dependency>
			<groupId>cglib</groupId>
			<artifactId>cglib</artifactId>
			<version>2.2.2</version>
		</dependency>
		<!-- Spring Data for MongoDB -->
		<dependency>
			<groupId>org.springframework.data</groupId>
			<artifactId>spring-data-mongodb</artifactId>
			<version>${springdata.version}</version>
		</dependency>
		<!-- Java MongoDB Driver -->
		<dependency>
			<groupId>org.mongodb</groupId>
			<artifactId>mongo-java-driver</artifactId>
			<version>${mongojavadriver.version}</version>
		</dependency>
	</dependencies>
	<build>
		<finalName>SpringData</finalName>
		<plugins>
		  <plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-compiler-plugin</artifactId>
			<version>2.3.2</version>
			<configuration>
				<source>${jdk.version}</source>
				<target>${jdk.version}</target>
			</configuration>
		  </plugin>
		</plugins>
	</build>
</project>

3. Sequence Collection

We create a collection name “sequence” to store the auto increase sequence id. Refer to the SequenceDaoImpl.java below, it shows you the code to generate the sequence id.

	db.sequence.insert({_id: "hosting",seq: 0})

package com.mkyong.seq.model;
import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;
@Document(collection = "sequence")
public class SequenceId {
	@Id
	private String id;
	private long seq;
	//get, set, toString...

package com.mkyong.seq.dao;
import com.mkyong.seq.exception.SequenceException;
public interface SequenceDao {
	long getNextSequenceId(String key) throws SequenceException;

package com.mkyong.seq.dao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.FindAndModifyOptions;
import org.springframework.data.mongodb.core.MongoOperations;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.core.query.Update;
import org.springframework.stereotype.Repository;
import com.mkyong.seq.exception.SequenceException;
import com.mkyong.seq.model.SequenceId;
@Repository
public class SequenceDaoImpl implements SequenceDao {
	@Autowired
	private MongoOperations mongoOperation;
	@Override
	public long getNextSequenceId(String key) throws SequenceException {
	  //get sequence id
	  Query query = new Query(Criteria.where("_id").is(key));
	  //increase sequence id by 1
	  Update update = new Update();
	  update.inc("seq", 1);
	  //return new increased id
	  FindAndModifyOptions options = new FindAndModifyOptions();
	  options.returnNew(true);
	  //this is the magic happened.
	  SequenceId seqId = 
            mongoOperation.findAndModify(query, update, options, SequenceId.class);
	  //if no id, throws SequenceException
          //optional, just a way to tell user when the sequence id is failed to generate.
	  if (seqId == null) {
		throw new SequenceException("Unable to get sequence id for key : " + key);
	  return seqId.getSeq();

package com.mkyong.seq.exception;
public class SequenceException extends RuntimeException {
	private static final long serialVersionUID = 1L;
	private String errCode;
	private String errMsg;
	//get, set...
	public SequenceException(String errMsg) {
		this.errMsg = errMsg;

4. Get the Sequence ID

To get the sequence id, uses sequenceDao.getNextSequenceId("key").

package com.mkyong.hosting.bo;
import com.mkyong.seq.exception.SequenceException;
public interface HostingBo {
	void save(String name) throws SequenceException;

package com.mkyong.hosting.bo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.mkyong.hosting.dao.HostingDao;
import com.mkyong.hosting.model.Hosting;
import com.mkyong.seq.dao.SequenceDao;
import com.mkyong.seq.exception.SequenceException;
@Service
public class HostingBoImpl implements HostingBo {
	private static final String HOSTING_SEQ_KEY = "hosting";
	@Autowired
	private SequenceDao sequenceDao;
	@Autowired
	private HostingDao hostingDao;
	@Override
	public void save(String name) throws SequenceException {
		Hosting hosting = new Hosting();
		hosting.setId(sequenceDao.getNextSequenceId(HOSTING_SEQ_KEY));
		hosting.setName(name);
		hostingDao.save(hosting);
		System.out.println(hosting);

5. Testing

Run a simple test.

package com.mkyong;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import com.mkyong.config.AppConfig;
import com.mkyong.hosting.bo.HostingBo;
import com.mkyong.seq.exception.SequenceException;
public class App {
  public static void main(String[] args) {
	ApplicationContext ctx = 
            new AnnotationConfigApplicationContext(AppConfig.class);
	HostingBo hostingBo = (HostingBo) ctx.getBean("hostingBoImpl");
	try {
		hostingBo.save("cloud.google.com");
		hostingBo.save("heroku.com");
		hostingBo.save("cloudbees.com");
	} catch (SequenceException e) {
		System.out.println(e.getErrMsg());

Output – Java console

Hosting [id=1, name=cloud.google.com]
Hosting [id=2, name=heroku.com]
Hosting [id=3, name=cloudbees.com]

MongoDB console.

>mongo
> db.sequence.find()
{ "_id" : "hosting", "seq" : 3 }
> db.hosting.find()
{ "_id" : NumberLong(1), "_class" : "com.mkyong.hosting.model.Hosting", "name" : "cloud.google.com" }
{ "_id" : NumberLong(2), "_class" : "com.mkyong.hosting.model.Hosting", "name" : "heroku.com" }
{ "_id" : NumberLong(3), "_class" : "com.mkyong.hosting.model.Hosting", "name" : "cloudbees.com" }
>

6. FAQs

Q. SequenceException – Unable to get sequence id for key : hosting ?
A. Remember to create the “sequence” collection!

	db.sequence.insert({_id: "hosting",seq: 0})

References

1. MongoDB – Create an Auto-Incrementing Sequence Field