Spring-data-mongodb connect to multiple databases

问题:

I am using the latest spring-data-mongodb (1.1.0.M2) and the latest Mongo Driver (2.9.0-RC1). I have a situation where I have multiple clients connecting to my application and I want to give each one their own "schema/database" in the same Mongo server. This is not a very difficult task to achieve if I was using the driver directly:

Mongo mongo = new Mongo( new DBAddress( "localhost", 127017 ) );

DB client1DB = mongo.getDB( "client1" );
DBCollection client1TTestCollection = client1DB.getCollection( "test" );
long client1TestCollectionCount = client1TTestCollection.count();

DB client2DB = mongo.getDB( "client2" );
DBCollection client2TTestCollection = client2DB.getCollection( "test" );
long client2TestCollectionCount = client2TTestCollection.count();

See, easy. But spring-data-mongodb does not allow an easy way to use multiple databases. The preferred way of setting up a connection to Mongo is to extend the AbstractMongoConfiguration class:

You will see that you override the following method:

getDatabaseName()

So it forces you to use one database name. The repository interfaces that you then build use that database name inside the MongoTemplate that is passed into the SimpleMongoRepository class.

Where on earth would I stick multiple database names? I have to make multiple database names, multiple MongoTempates (one per database name), and multiple other config classes. And that still doesn't get my repository interfaces to use the correct template. If anyone has tried such a thing let me know. If I figure it out I will post the answer here.

Thanks.

回答1:

Here is a link to an article I think is what you are looking for http://michaelbarnesjr.wordpress.com/2012/01/19/spring-data-mongo/

The key is to provide multiple templates

configure a template for each database.

<bean id="vehicleTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
    <constructor-arg ref="mongoConnection"/>
    <constructor-arg name="databaseName" value="vehicledatabase"/>
</bean>

configure a template for each database.

<bean id="imageTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
        <constructor-arg ref="mongoConnection"/>
        <constructor-arg name="databaseName" value="imagedatabase"/>
</bean>

<bean id="vehicleTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
    <constructor-arg ref="mongoConnection"/>
    <constructor-arg name="databaseName" value="vehicledatabase"/>
</bean>

Now, you need to tell Spring where your repositories are so it can inject them. They must all be in the same directory. I tried to have them in different sub-directories, and it did not work correctly. So they are all in the repository directory.

<mongo:repositories base-package="my.package.repository">
    <mongo:repository id="imageRepository" mongo-template-ref="imageTemplate"/>
    <mongo:repository id="carRepository" mongo-template-ref="vehicleTemplate"/>
    <mongo:repository id="truckRepository" mongo-template-ref="vehicleTemplate"/>
</mongo:repositories>

Each repository is an Interface and is written as follows (yes, you can leave them blank):

@Repository
public interface ImageRepository extends MongoRepository<Image, String> {

}

@Repository
public interface TruckRepository extends MongoRepository<Truck, String> {

}

The name of the private variable imageRepository is the collection! Image.java will be saved to the image collection within the imagedb database.

Here is how you can find, insert, and delete records:

@Service
public class ImageService {

    @Autowired
    private ImageRepository imageRepository;
}

By Autowiring you match the variable name to the name (id) in your configuration.

回答2:

You may want to sub-class SimpleMongoDbFactory and strategize how the default DB as returned by getDb is returned. One option is to use thread-local variables to decide on the Db to use, instead of using multiple MongoTemplates.

Something like this:

public class ThreadLocalDbNameMongoDbFactory extends SimpleMongoDbFactory {
    private static final ThreadLocal<String> dbName = new ThreadLocal<String>();
    private final String defaultName; // init in c'tor before calling super

    // omitted constructor for clarity

    public static void setDefaultNameForCurrentThread(String tlName) {
        dbName.set(tlName);
    }
    public static void clearDefaultNameForCurrentThread() {
        dbName.remove();
    }

    public DB getDb() {
        String tlName = dbName.get();
        return super.getDb(tlName != null ? tlName : defaultName);
    }
}

Then, override mongoDBFactory() in your @Configuration class that extends from AbstractMongoConfiguration like so:

@Bean
@Override
public MongoDbFactory mongoDbFactory() throws Exception {
  if (getUserCredentials() == null) {
      return new ThreadLocalDbNameMongoDbFactory(mongo(), getDatabaseName());
  } else {
      return new ThreadLocalDbNameMongoDbFactory(mongo(), getDatabaseName(), getUserCredentials());
  }
}

In your client code (maybe a ServletFilter or some such) you will need to call: ThreadLocalDBNameMongoRepository.setDefaultNameForCurrentThread() before doing any Mongo work and subsequently reset it with: ThreadLocalDBNameMongoRepository.clearDefaultNameForCurrentThread() after you are done.

回答3:

So after much research and experimentation, I have concluded that this is not yet possibly with the current spring-data-mongodb project. I tried baja's method above and ran into a specific hurdle. The MongoTemplate runs its ensureIndexes() method from within its constructor. This method calls out the the database to make sure annotated indexes exist in the database. The constructor for MongoTemplate gets called when Spring starts up so I never even have a chance to set a ThreadLocal variable. I have to have a default already set when Spring starts, then change it when a request comes in. This is not allowable because I don't want nor do I have a default database.

All was not lost though. Our original plan was to have each client running on its own application server, pointed at its own MongoDB database on the MongoDB server. Then we can provide a -Dprovider= system variable and each server runs pointing only to one database.

We were instructed to have a multi-tenant application, hence the attempt at the ThreadLocal variable. But since it did not work, we were able to run the application the way we had originally designed.

I believe there is a way though to make this all work, it just takes more than is described in the other posts. You have to make your own RepositoryFactoryBean. Here is the example from the Spring Data MongoDB Reference Docs. You would still have to implement your own MongoTemplate and delay or remove the ensureIndexes() call. But you would have to rewrite a few classes to make sure your MongoTemplate is called instead of Spring's. In other words, a lot of work. Work that I would like to see happen or even do, I just did not have the time.

Thanks for the responses.

回答4:

The spot to look at is the MongoDbFactory interface. The basic implementation of that takes a Mongo instance and works with that throughout all the application lifetime. To achieve a per-thread (and thus per-request) database usage you'll probably have to implement something along the lines of AbstractRoutingDataSource. The idea is pretty much that you have a template method that will have to lookup the tenant per invocation (ThreadLocal bound I guess) and then select a Mongo instance from a set of predefined ones or some custom logic to come up with a fresh one for a new tenant etc.

Keep in mind that MongoDbFactory usually get's used through the getDb() method. However, there are features in MongoDB that need us to provide a getDb(String name). DBRefs (sth. like a foreign key in the relational world) can point to documents an entirely different database. So if you're doing the delegation either avoid using that feature (I think the DBRefs pointing to another DB are the only places calling getDb(name)) or explicitly handle it.

From a configuration point of view you could either simply override mongoDbFactory() entirely or simply not extend the base class at all and come up with your own Java based configuration.

回答5:

I used different DB using java Config, this is how i did it:

@Bean 
public MongoDbFactory mongoRestDbFactory() throws Exception { 
    MongoClientURI uri=new MongoClientURI(environment.getProperty("mongo.uri")); 
    return new SimpleMongoDbFactory(uri);
}

@Override
public String getDatabaseName() {
    return "rest";
}

@Override
public @Bean(name = "secondaryMongoTemplate") MongoTemplate mongoTemplate() throws Exception{ //hay que cambiar el nombre de los templates para que el contendor de beans sepa la diferencia  
    return new MongoTemplate(mongoRestDbFactory());    
}

And the other was like this:

@Bean 
public MongoDbFactory restDbFactory() throws Exception {
    MongoClientURI uri = new MongoClientURI(environment.getProperty("mongo.urirestaurants")); 
    return new SimpleMongoDbFactory(uri);
}

@Override
public String getDatabaseName() {
    return "rest";
}

@Override
public @Bean(name = "primaryMongoTemplate") MongoTemplate mongoTemplate() throws Exception{ 
    return new MongoTemplate(restDbFactory());    
}

So when i need to change my database i only select which Config to use

回答6:

As far as I understand, you want more flexibility in changing the current db on the fly.

I've linked a project that implements multi tenancy in a simple way.

It could be used as a starting point for the application.

It implements SimpleMongoDbFactory and provide a custom getDB method to resolve the correct db to use in certain moment. It can be improved in many ways, for example, by retrieving the db details from a HttpSession from SpringSession object, which for instance could be cached by Redis .

To have different mongoTemplates using different dbs at the same time, maybe change the scope of your mongoDbFactory to session.

References:

multi-tenant-spring-mongodb