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Untitled

QuipuKit 1.6.2: JSF library with a set of advanced UI components and clientside validation http://bit.ly/eLJum

Unique Constraint with Hibernate Validator and Spring

Sometime ago I was fighting with Hibernate Validator, trying to implement an unique constraint and I could not figure out how to create one that requires database access:

The problem is that your validators can't access sessionFactory or any other interface to the database. I know that I can break some rules and instantiate a sessionFactory/session/connection directly inside the Validator, but I dislike to do wrong things consciously. So, I looking for alternatives.

Then, while studying the new validation support offered by Spring, I just discovery that using Spring I can inject any bean inside my ConstraintValidators. From Spring documentation:

By default, the LocalValidatorFactoryBean configures a SpringConstraintValidatorFactory that uses Spring to create ConstraintValidator instances. This allows your custom ConstraintValidators to benefit from dependency injection like any other Spring bean.

And here is how you can use that Spring feature to implement unique constraint.

THE UNIQUE ANNOTATION

It is very simple and direct. You can see details about implementing your custom annotations in Hibernate Validator docs.

@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy=UniqueConstraintValidator.class)
@Documented
public @interface Unique {
    String message() default "{constraints.unique}";
    Class<?> entity();
    String field();
    Class<?>[] groups() default {};   
    Class<? extends Payload>[] payload() default {};
}

You can also see the code at GitHub, where trapo is hosted. If I decide to change something, you can get an updated version there. Once you have the @Unique annotation, you must implement the ConstraintValidator referenced by "validationBy" property in @Constraint annotation above. Here is the code using a bean injected by Spring:

public class UniqueConstraintValidator implements ConstraintValidator<Unique, String> {

    @Autowired private SessionFactory sessionFactory;
   
    private Class<?> entity;
    private String field;
   
    public void initialize(Unique annotation) {
        this.entity = annotation.entity();
        this.field = annotation.field();
    }

    public boolean isValid(String value, ConstraintValidatorContext context) {
        if(StringUtils.isEmpty(value)) {
            return false;
        }
        return query(value).intValue() == 0;
    }

    private Number query(String value) {
        HibernateTemplate template = new HibernateTemplate(sessionFactory);
        DetachedCriteria criteria = forClass(entity)
                                   .add(eq(field, value))
                                   .setProjection(count(field));
        return (Number)template.findByCriteria(criteria).iterator().next();
    }

}

Just like the @Unique annotation, you can find the code in GitHub. Now you just need a Validator bean that can be injected in the classes that need it.

<bean id="validator"
      class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean" />

Voilá!

THE UGLY PART

Right now, Hibernate Validor don't offer any way to know from where your annotations are coming. If you take some time to think about the ConstraintValidator above, you will notice that I manually configure the entity class and field information that were annotated. I need that information to know what query I must execute in order to validate the uniqueness of the field. Bad to me. Really bad. Now I have to provide this information by myself annotating the field like the code highlighted below:

    @NotEmpty @Unique(entity = Forum.class, field = "name")
    private String name;

I can even hear the DRY concept crying! I can't also find a way to reflect this to my schema. Maybe Hibernate Validator can offer some interfaces that we can use to implement all this stuff.

Includes and wasted effort

W3C says <link> and <style> should only be in the <head>. Why am i concerned with validation? I'm not; so I was originally alright with my first attempt to reduce code repetition.

Each page has a very similar top and an identical bottom.The problem with the top is in the included scripts and styles. All pages load corners. Some load fancy box. one loads visualize. Each of these has its own style sheet. Additionally each page has a different title, some custom style, and a unique position in the navigation display. I'd like include both in one gutted file and then load the meat on demand from external files. I could take care of loading uncommon styles and scrips simply by including them in the body. This works on firefox at least. The title and nav display could easily be handled by on click action, passing an argument or (as is the current implementation) deducing from the url. Also, broken up like this, I could add fancy effects by loading with the data via $.ajax in jQuery. So I did all of this, the whole time thinking hash marks in the url would add sufficient browser aware navigation (a working back button).  This was not the case.
content transitioned with beautiful fades while the bottom and top were able to stay static. It looked professional. But the back button did nothing. Each page changed window.location.hash. but the browser didn't care or remember the last real "GET." Disappointing. Worse, I didn't spend enough time to figure out how facebook or gmail does it. It was too cumbersome to implement anyway. I was doing this to save work (while avoiding actually doing something productive).
Instead of breaking the load into two files: one with most static stuff that calls in the real content. I've done two static-ish pages (top and bottom) and one page the meat that calls in the other two. I load uncommon scripts and styles, then the top, do the heavy lifiting, and then call in the bottom. No more fancy effects. But the code is clearer, authentication can be done in the top and doesn't have to be repeated (php include works so the $user variable established and potentially authenticated in the top container is accessible and therefore actionable to the including script.) The only remaining hick-up is navigation customization per page. Because it's in the middle of the top content, I didn't want to truncate the top and extend each content page. And i didn't want to include two different top pages just to figure out which anchor tag to put the current class on. Instead I came up with this ugly hack.

/*ugly ugly ugly way to set get current location for sytling navigation*/
    $current = preg_replace("/.*\/(.*).php.*/", "$1", $_SERVER["REQUEST_URI"], 1); 
    $hascurrent= array( 'home' => '', 'dashboard' => '', 'new' => '',  'edit' => '', 'publish' => '' );
     $hascurrent[$current] = ' class="current" ';

and then later in the php file

<li style="padding-left:0px">
            <?php echo $hascurrent['home']?>>My Account</li>
         <li><?php echo $hascurrent['new'] . $hascurrent['edit']. $hascurrent['publish']?>
                                >Build a Case</li>
         <li><?php echo $hascurrent['dashboard']?>>Case Dashboard</li>
        <li>Help</li>
 

I get a name from the url, removing the junk before and after the relevant part of the file name using preg_replace. Where all value are otherwise ' ', I add 'class=curernt' to the element of the hascurrent array called by that name of the file. Then I ask for the value of each array by this name in on the approprate link in the navigation portion. Nothing but whitespace will be added unless the current file name is called. Then the class=current is injected. Ugly, but functioning.

Our first iPhone app

iPhone Developer Challenges

Apple is known for their innovation and support. It is clear that there is a very specific development cycle within the software group. This process is very guarded and up until right before release, the features are typically unknown. This makes it tough for application developers to plan products that have and longevity, if they aren't immediately included in an OS release.

Validation is a wonderful thing

Validated!

Do you need a validation? Watch on!

 

Translating a Nerd

I quote below from an American nerd athlete artist.  He's relieved at the American electorate's ability to choose the intellectual candidate.  But his comment intends to celebrate neither American nor Chinese culture.

We live in a country where the nerd gets beaten up in middle school.  In China, the nerd is the bully.

I did not know this about China when I lived there.  I never saw it happen, never heard stories about it until today.  But it does make sense.  Good grades earn big teacher love and, with it, positions of authority in classrooms.  And there doesn't exist a school-connected athletic infrastructure to balance the power.  Validation comes first for the successfully academic minds and significantly later, if at all, for anyone else.

Anyone have any experience with this?  I'd love to know more.