How do I inject service-like components to Grails domain objects? - grails

Question

I've never used Grails services before, but according to my Web searches, they can be injected into domain objects. So, if I have the following domain class (assume that BookService is defined somewhere),
class Book {
BookService bookService
}
when I instantiate a Book object using, def book = new Book(), book.bookService should be set?
If that's the case, what if I want to inject external services (or service-like components)? For example, if there's an ISBN API client available, can I expect grails to inject it the same way? For example, say the client is IsbnApi, how do I automatically inject like it's another service? Will the code below work?
class Book {
#Transient
#Autowire
IsbnApi isbnApi
}
Based on the earlier responses to this question, I've already defined the domain class this way:
class Book {
static transients = ['isbnApi']
IsbnApi isbnApi
}
Now, this may be all that I need, but I also want to test that the automatic injection would work even without having to run the app. In my unit tests, I have to set the mock "service" manually.
IsbnApi isbnApi = Mock()
Book book = new Book()
book.isbnApi = mockIsbnApi
I attempted to check automatic injection by moving the test to test/integration and set the beans using doWithSpring.
def doWithSpring() {
isbnApi = (InstanceFactoryBean, mockIsbnApi, isbnApi)
}
void "test automatic injection"() {
given:
IsbnApi isbnApi = Mock()
Book book = new Book()
//removed: book.isbnApi = mockIsbnApi
expect:
book.isbnApi //this fails
}
I also found additional information from this answer to a similar question. In particular,
Note that since you're using 'def' you don't need to add it to the
transients list. Are you trying to access it from a static method?
It's an instance field, so you can only access it from instances.

Answer 1

By convention Grails services are automatically candidates for dependency injection (= they can be injected into other classes). If you want to other classes you have to add them to conf/spring/resources.groovy.
E.g.:
import foo.bar.IsbnApi
beans = {
isbnApi(IsbnApi)
}
Have a look at the Bean Builder documentation section.
To make sure that your field is not treat as a persistent property, you can use the static transients field.
For example:
class User {
def grailsApplication
static transients = ['grailsApplication']
}
See transients documentation

Answer 2

In addition to the already accepted answers, as from grails 3.2.x you will need to enable autowiring on the domain ojbect in the mapping block or globally in the application config
class Book {
static transients = ['isbnApi']
IsbnApi isbnApi
static mapping = {
autowire true
}
}
It is disabled by default to improve read performance so perhaps it's best to find alternative approach instead of enabling it.
http://grailsblog.objectcomputing.com/posts/2017/05/09/injecting-a-service-into-a-domain-class.html