DDevelopment & Design

Using GORM standalone

Few days ago we decided to get rid of Apache iBatis in one of our projects. We couldn’t longer maintain large XML mapping and query descriptors with mix of Java, SQL and XML itself. But we also wanted to avoid switching to another ORM framework with lot of features and DAO layer requirement. We tried to implement some simple Spring JdbcTemplate-based ORM in Groovy, but it (strangely) started to look just like Hibernate… All that aliases in generated SQL’s, need to use javax.presistence annotations etc. The only simple existing solutions were Groovy’s DataSet (which is not working outside Groovy script) and GORM. Googling ‘GORM standalone’ show just few useful, but rather outdated, results. So I was forced to spend couple of hours to write desired 6 lines of code:

ExpandoMetaClass.enableGlobally()
        SessionFactory sessionFactory = ctx.getBean("sessionFactory")
        def grailsApp = new DefaultGrailsApplication([Customer.class] as Class[], null)
        grailsApp.initialise()
        GrailsHibernateUtil.configureHibernateDomainClasses(sessionFactory, grailsApp)
        HibernatePluginSupport.enhanceSessionFactory(sessionFactory, grailsApp, ctx)

And after annotating Customer class:

@Entity
@Table(name = "CUSTOMERS")
class Customer {
    String firstName
    String lastName
}

Now we are able to enjoy DAO-less code in pure Groovy:

Customer.findAll().each{ println it.firstName }         
        Customer.withCriteria { eq('lastName', 'Smith') }.each { Customer c -> println c.firstName }
        Customer.findByFirstNameAndLastName('John', 'Smith')

PS. For unknown reasons, these 6 lines work only with Grails 1.1.x

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DDevelopment & Design

Inconsistent Dependency Injection to domains with Grails

I've encountered strange behavior with a domain class in my project: services that should be injected were null. I've became suspicious as why is that? Services are injected properly in other domain classes so why this one is different?

Constructors experiment

I've created an experiment. I've created empty LibraryService that should be injected and Book domain class like this:

class Book {
    def libraryService

    String author
    String title
    int pageCount

    Book() {
        println("Finished constructor Book()")
    }

    Book(String author) {
        this()
        this.@author = author
        println("Finished constructor Book(String author)")
    }

    Book(String author, String title) {
        super()
        this.@author = author
        this.@title = title
        println("Finished constructor Book(String author, String title)")
    }

    Book(String author, String title, int pageCount) {
        this.@author = author
        this.@title = title
        this.@pageCount = pageCount
        println("Finished constructor Book(String author, String title, int pageCount)")
    }

    void logInjectedService() {
        println("    Service libraryService is injected? -> $libraryService")
    }
}
class LibraryService {
    def serviceMethod() {
    }
}

Book has 4 explicit constructors. I want to check which constructor is injecting dependecies. This is my method that constructs Book objects and I called it in controller: 

class BookController {
    def index() {
        constructAndExamineBooks()
    }

    static constructAndExamineBooks() {
        println("Started constructAndExamineBooks")
        Book book1 = new Book().logInjectedService()
        Book book2 = new Book("foo").logInjectedService()
        Book book3 = new Book("foo", 'bar').logInjectedService()
        Book book4 = new Book("foo", 'bar', 100).logInjectedService()
        Book book5 = new Book(author: "foo", title: 'bar')
        println("Finished constructor Book(Map params)")
        book5.logInjectedService()
    }
}

Analysis

Output looks like this:

Started constructAndExamineBooks
Finished constructor Book()
    Service libraryService is injected? -> eu.spoonman.refaktor.LibraryService@2affcce2
Finished constructor Book()
Finished constructor Book(String author)
    Service libraryService is injected? -> eu.spoonman.refaktor.LibraryService@2affcce2
Finished constructor Book(String author, String title)
    Service libraryService is injected? -> null
Finished constructor Book(String author, String title, int pageCount)
    Service libraryService is injected? -> null
Finished constructor Book()
Finished constructor Book(Map params)
    Service libraryService is injected? -> eu.spoonman.refaktor.LibraryService@2affcce2

What do we see?

  1. ✔

    Empty constructor injects dependencies.

  2. ✔

    Constructor that invokes empty constructor explicitly injects dependencies.

  3. ✘

    Constructor that invokes parent's constructor explicitly does not inject dependencies.

  4. ✘

    Constructor without any explicit call declared does not call empty constructor thus it does not inject dependencies.

  5. ✔

    Constructor provied by Grails with a map as a parameter invokes empty constructor and injects dependencies.

Conclusion

Always explicitily invoke empty constructor in your Grail domain classes to ensure Dependency Injection! I didn't know until today either!