Dependency injection using Guice with the DAO pattern

Question

For a small side project I\'m working on I\'ve been trying to implement something of a DAO pattern for my interactions with the DB, and have started using Guice (for my first ti

Answer 1

If you want an injection site like the following:

@Inject
public DAOConsumer(DAO<User> dao) {
}

to be injected with an instance of your UserDAO class then

bind(new TypeLiteral<DAO<User>>() {}).to(UserDAO.class);

is the correct syntax.

As for your other error:

1) No implementation for org.mongodb.morphia.Datastore was bound.

This is because Datastore is an interface. You need to bind the interface to an implementation, an instance, or a Provider<Datastore>.

To work out how to do this, think of the steps you would need to do this manually without the extra complication of Guice. Once you 100% understand this, you can try and design an object graph that appropriately reflects the steps in the initialization of morphia.

To get you started, the morphia quick tour has a guide on how to get an instance of the Datastore object:

final Morphia morphia = new Morphia();

// tell Morphia where to find your classes
// can be called multiple times with different packages or classes
morphia.mapPackage("org.mongodb.morphia.example");

// create the Datastore connecting to the default port on the local host
final Datastore datastore = morphia.createDatastore(new MongoClient(), "morphia_example");
datastore.ensureIndexes();

From their code, you can see that there are at least two dependencies required to get the Datastore:

1. A singleton Morphia
2. A singleton MongoClient

You will have to write some code to set this up, possibly using Guice's Provider class.