Wednesday, July 27, 2011

Exploiting MongoDB together with Spring Data project: basic concepts

All of us are observing the explosion of NoSql solutions these days. I get used to RDBMS but those are not a solution for all kind of challenges you might have. In my recent experience I got a chance to work with MongoDB - document database. In this post I intent to cover some basics (and some advanced features in next post) of using MongoDB together with Spring Data project. Before we start, small disclaimer: at the moment Spring Data is still in milestone phase so some classes / interfaces may change.

Before we start, please download and run MongoDB for your operating system. It's very simple so I won't spend time on this and let's start with simple POM file for our project:
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    <modelversion>4.0.0</modelversion>
 
    <groupid>mongodb</groupid>
    <artifactid>com.example.spring</artifactid>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
 
    <properties>
        <project.build.sourceencoding>UTF-8</project.build.sourceencoding>
        <spring.version>3.0.5.RELEASE</spring.version>
    </properties>
 
    <dependencies>
        <dependency>
            <groupid>org.springframework.data</groupid>
            <artifactid>spring-data-mongodb</artifactid>
            <version>1.0.0.M3</version>
        </dependency>
 
        <dependency>
            <groupid>log4j</groupid>
            <artifactid>log4j</artifactid>
            <version>1.2.16</version>
        </dependency>
 
        <dependency>
            <groupid>org.mongodb</groupid>
            <artifactid>mongo-java-driver</artifactid>
            <version>2.5.3</version>
        </dependency>
 
        <dependency>
            <groupid>org.springframework</groupid>
            <artifactid>spring-core</artifactid>
            <version>${spring.version}</version>
        </dependency>
 
        <dependency>
            <groupid>org.springframework</groupid>
            <artifactid>spring-context</artifactid>
            <version>${spring.version}</version>
        </dependency>
    </dependencies>
 
    <repositories>
        <repository>
            <id>springsource-milestone</id>
            <name>Spring Framework Milestone Repository</name>
            <url>http://maven.springframework.org/milestone</url>
        </repository>
    </repositories>
</project>
There are two key dependencies here:
- MongoDB java driver
- Spring Data for MongoDB

There are few ways to define MongoDB inside your Spring application context. Let me show a bit verbose but more flexible one:
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    <context:annotation-config></context:annotation-config>
    <context:component-scan base-package="com.example.mongodb"></context:component-scan>
   
    <mongo:jmx></mongo:jmx>
  
    <bean id="mongoDbFactory" class="org.springframework.data.document.mongodb.SimpleMongoDbFactory">
        <constructor-arg index="0" ref="mongo" />
        <constructor-arg index="1" value="elements-db"/>
    </bean>
 
    <bean id="mappingContext" class="org.springframework.data.document.mongodb.mapping.MongoMappingContext">   
    </bean
 
    <bean id="converter" class="org.springframework.data.document.mongodb.convert.MappingMongoConverter">
        <constructor-arg name="mongoDbFactory" ref="mongoDbFactory" />
        <constructor-arg name="mappingContext" ref="mappingContext" />        
    </bean>
 
    <bean id="mongoTemplate" class="org.springframework.data.document.mongodb.MongoTemplate">
        <constructor-arg name="mongoDbFactory" ref="mongoDbFactory"/>
        <constructor-arg name="mongoConverter" ref="converter" />       
        <property name="writeResultChecking" value="EXCEPTION" />
        <property name="writeConcern" value="NORMAL"/>
    </bean>
  
    <bean id="mongo" class="org.springframework.data.document.mongodb.MongoFactoryBean">
        <property name="host" value="localhost"></property>
    </bean>
</beans>
The role of each bean here:
  • mongo defines connection to MongoDB database (we rely on default settings, port 27027)
  • converter is used to convert Java classes to/from MongoDB's DBObject (== JSON)
  • mongoTemplate exposes operations we can do over MongoDB

So, we are ready to go!
Here are few code snippets to start with:
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package com.example.mongodb;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.dao.DataAccessException;
import org.springframework.data.document.mongodb.CollectionCallback;
import org.springframework.data.document.mongodb.MongoOperations;
import org.springframework.data.document.mongodb.query.Index;
import org.springframework.data.document.mongodb.query.Index.Duplicates;
import org.springframework.data.document.mongodb.query.Order;
import org.springframework.stereotype.Service;
 
import com.mongodb.BasicDBObject;
import com.mongodb.DBCollection;
import com.mongodb.MongoException;
 
@Service
public class MongoService  {
    @Autowired private MongoOperations template;
 
    public void createCollection( final String name ) {
        template.createCollection( name  );
    }
 
    public void dropCollection( final String name ) {
        template.dropCollection( name  );
    }
 
    public void insert( final Object object, final String collection ) {
        template.insert( object, collection );
    }
    
    public void createIndex( final String name, final String collection ) {
        template.ensureIndex(
            new Index()
                .on( name, Order.DESCENDING )
                .unique( Duplicates.DROP ),
            collection 
        );
    }
  
    // Remove / save / ... operations here
}
That's it with basics. Next post will cover advanced features: using bulk inserts, update or insert operation and executing MongoDB commands. :)

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