How to use low-level driver APIs with Spring Data MongoDB - spring

Question

I am using Spring Data MongoDB. But I don't want to map my result to a domain class. Also, I want to access low level MongoAB APIs in few cases. But I want spring to manage the connections pooling etc.
How can i get an instance of com.mongodb.MongoClient to perform low level operations.
Here is what I am trying to do :
MongoClient mongoClient = new MongoClient();
DB local = mongoClient.getDB("local");
DBCollection oplog = local.getCollection("oplog.$main");
DBCursor lastCursor = oplog.find().sort(new BasicDBObject("$natural", -1)).limit(1);
Or I simply want a JSON object / DBCursor / DBObject.

Answer 1

you can do it this way
#Autowired MongoDbFactory factory;
DB local = factory.getDB("local");
DBCollection oplog = local.getCollection("oplog.$main");
DBCursor lastCursor = oplog.find().sort(new BasicDBObject("$natural", -1)).limit(1);
Where
MongoDbFactory is an interface provifed by spring-data-mongo that can obtain a
com.mongodb.DB object and access allthe functionality of a specific MongoDB database
instance
your configuration file should contain these informations :
<bean id="mongoFactoryBean"
class="org.springframework.data.mongodb.core.MongoFactoryBean">
<property name="host" value="127.0.0.1"/>
<property name="port" value="27017"/>
</bean>
<bean id="mongoDbFactory"
class="org.springframework.data.mongodb.core.SimpleMongoDbFactory">
<constructor-arg name="mongo" ref="mongoFactoryBean"/>
<constructor-arg name="databaseName" value="local"/>
</bean>
doing it like that, spring should stay managing your connection pool.

Answer 2

You usually perform low level access through MongoTemplate's execute(…) methods that take callbacks giving you access to the native Mongo driver API.
class MyClient {
private final MongoOperations operations;
#Autowired
public MyClient(MongoOperations mongoOperations) {
this.operations = operations;
}
void yourMethod() {
operations.execute(new CollectionCallback<YourDomainClass>() {
YourDomainClass doInCollection(DBCollection collection) {
// here goes your low-level code
}
});
}
The advantage of this template approach is that the MongoTemplate instance backing the MongoOperations interface will still take care of all resource management and exception translation (converting all Mongo specific exceptions into Spring's DataAccessException hierarchy).
However, for your concrete example you could just go ahead and do the following directly:
Query query = new Query().with(new Sort(DESC, "$natural")).limit(1);
DBObject result = operations.find(query, DBObject.class, "oplog.$main");
Here you can mix and match the type you pass into the find(…) method to let the template convert the result into a Map or a domain object if needed. As indicated above you also get resource management and exception translation which your sample code above is missing.