Inject only direct dependencies

Avoid injecting an object only as a means to get at another object. For example, don't inject a Customer as a means to get at an Account:

public class ShowBudgets { 
   private final Account account; 

   @Inject 
   ShowBudgets(Customer customer) { 
     account = customer.getPurchasingAccount(); 
   }

Instead, inject the dependency directly. This makes testing easier; the test case doesn't need to concern itself with the customer. Use an @Provides method in your Module to create the binding for Account that uses the binding for Customer:

public class CustomersModule extends AbstractModule { 
  @Override public void configure() {
    ...
  }

  @Provides 
  Account providePurchasingAccount(Customer customer) { 
    return customer.getPurchasingAccount();
  }

By injecting the dependency directly, our code is simpler.

public class ShowBudgets { 
   private final Account account; 

   @Inject 
   ShowBudgets(Account account) { 
     this.account = account; 
   }

Comment by brhargett@gmail.com, May 20, 2009

If you want the account of a certain customer how would you handle that outside of doing it the 1st way (customer.getAccount())?

Comment by project member ffa...@gmail.com, Aug 6, 2009

You would bind the Account and have that injected in. If you know your customer at configure() time, then you'll know your Account.

As a simple example, you could have:

bind(Account.class)

.toProvider(new Provider<Account>() {
@Inject Customer customer;

@Override public Account get() {
return customer.getAccount();
}

});

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