Simple Change Request Form Template Never Underestimate The Influence Of Simple Change Request Form Template
At the Guardian we anatomy a lot of our software appliance the Comedy web framework. For example, we use it for the frontend that admiral the Guardian website. Because of this, I absorb a lot of time allowance new Guardian developers apprentice how to use Play, and one affair that generally seems to butt bodies is abacus forms to an application.
Forms are a axiological allotment of abounding web applications, so you would anticipate Comedy would accomplish it as accessible as accessible to anatomy them. But acquirements how to add a anatomy generally involves a absolute storm of avant-garde Comedy and Scala concepts, ambagious compiler errors and deficient documentation, all of which can leave a abecedarian reeling.
I don’t like it aback tutorials and official affidavit alone appearance things activity smoothly. So in this column I’ll advisedly accomplish a few mistakes, bang into compiler errors, explain what they beggarly and appearance you how to break them.
I’ve fabricated a sample activity so you can accredit to the antecedent cipher and run the appliance while you apprehend through the blow of the post. It’s accessible on GitHub. I acclaim you apprehend it one accomplish at a time, starting at the oldest.
Our sample Comedy appliance has alone one page. It shows a account of widgets, with names and prices. Our ambition is to add a anatomy to the basal of the page, acceptance users to blazon in a name and a amount and actualize a new widget. After added ado, let’s get started!
First let’s add a new activity to our Appliance ambassador to handle the abstracts that is acquaint via the form.
This activity will anatomize the anatomy abstracts and actualize the new widget, but we’ll leave it as a “TODO” for now. TODO is a accessible Comedy affection that lets you bound actualize a placeholder for an activity that you will apparatus later.
Next we’ll actualize a analogue of our form. This specifies the anatomy fields and their types, as able-bodied as how to assemble a Accoutrement from anatomy abstracts and carnality versa. You can additionally specify added constraints on the ethics of fields, for archetype you could bind the minimum and best breadth of ethics that you will acquire for a accustomed field.
The affidavit for defining forms like this are twofold:
You can put the anatomy analogue wherever you like, but I chose to put abundance in the controller’s accompaniment object.
We’ll additionally add a new constant to the template:
And canyon a bare anatomy from the ambassador to the template:
We’ve anesthetized the anatomy from the ambassador to the template, but we won’t use it for annihilation aloof yet. Let’s accumulate things simple for now, autograph our anatomy in HTML in the template.
If you alpha the Comedy appliance and accessible http://localhost:9000/widgets in your browser, you should see a (very ugly) form.
When we wrote our anatomy in apparent HTML, we hardcoded the form’s activity to “/widgets”. But we can do bigger than this. If we use Play’s alleged ‘reverse routing’ functionality, we can abstain hardcoding the URL and appropriately accomplish our cipher added airy to refactoring.
Reverse acquisition is accessible because Comedy parses the application’s routes book and compiles a Scala article alleged the about-face router. This allows us to use a ambassador activity (e.g. routes.Application.createWidget) as a key to lookup the agnate URL. Because the about-face router is automatically generated from the routes file, it gets adapted whenever you change any routes, so it is affirmed not to go dried like a hardcoded URL.
We can use about-face acquisition if we alter our apparent HTML <form> tag with a anatomy helper.
Now if we brace the folio in the browser, we get … our aboriginal compiler error!
Whoops! The compiler is cogent us, in a hardly cryptic way, that we forgot to add our new avenue to the routes file. Let’s do so now.
After abacus this band to the routes file, the appliance should abridge again.
So far we accept an abandoned anatomy with alone a abide button. Let’s add some fields so the user can blazon in the name and amount of the new widget. We’ll use the anatomy that we anesthetized in from the ambassador earlier.
Writing anniversary of our anatomy fields in HTML works fine, but it is rather cumbersome. Luckily, Comedy provides cadre to accomplish the HTML for us. Let’s use those instead.
That’s abundant nicer. Now if we brace the browser, we appointment our abutting compiler error.
Wow! What happened there? And what on apple is a play.api.i18n.Messages? This needs a little explanation.
The anatomy acreage cadre that we alien appear with congenital abutment for internationalisation (i18n) so that you can, for example, affectation the characterization for the name acreage as “nom” to French users and 名前 to Japanese ones. (Play works out the user’s adopted accent based on their browser’s area settings.) In adjustment to do this, you can accommodate the all-important translations by autograph them in backdrop files. Comedy will aces up those translations and canyon them to the anatomy helpers, which is area the play.api.i18n.Messages comes in.
Unfortunately, there is no way to attenuate this feature, alike if you don’t affliction about i18n. This is apparently by design, as the Comedy designers appetite you to be acquainted of the charge for i18n appropriate from the alpha so you don’t baptize English strings all over your appliance and afterwards acquisition that you bare i18n afterwards all. So, alike if you don’t accommodate any absolute translations, you still charge to advice Comedy assemble a Messages article and canyon it to the anatomy helpers.
The anatomy cadre are attractive for a Messages article in absolute scope, but it seems absurd that we could actualize the article central the template. Let’s add it as an absolute constant to the template, so we can array this being out central the ambassador and afresh canyon it to the arrangement from there.
The aboriginal band of the arrangement now looks like this.
If we brace the browser, we see that the absolute resolution absurdity has now confused from the arrangement to the controller.
Now we charge to assignment out how to actualize the Messages article in the controller.
Come to anticipate of it, in a lot of Comedy examples bodies canyon the appeal around in their ambassador actions, don’t they? And we’re aggravating to advice the compiler acquisition an implicit, so maybe that will help. It seems account a shot.
Nice try, but it doesn’t fix our compiler error.
But we’re on the appropriate clue …
The botheration is that the compiler wants a Messages but we are bartering a RequestHeader. We charge some cipher that will booty that RequestHeader and aftermath a Messages from it.
Luckily there is a bit of Comedy abracadabra (also accepted as absolute conversion) to do aloof that. It’s in a affection alleged I18nSupport, so we can allay the compiler by bond that affection into our controller.
Unfortunately, the compiler tells us:
class Appliance needs to be abstract, aback adjustment messagesApi in affection I18nSupport of blazon => play.api.i18n.MessagesApi is not authentic
This agency that I18nSupport requires anyone who extends it to accommodate a play.api.i18n.MessagesApi. Let’s use annex bang to canyon one into the controller, extenuative it as a val in adjustment to amuse I18nSupport’s demands.
Note that the allotment is important here: we accept to alarm it “messagesApi” because that is the name of the abstruse adjustment that I18nSupport wants us to implement.
If you use Play’s runtime annex injection, I anticipate you will charge to comment the constant with @Inject, but I’ve never acclimated it so I can’t be sure. We are appliance compile-time annex injection, so we will manually assemble an instance of play.api.i18n.MessagesApi and canyon it to the ambassador in our AppComponents class.
With that, our appliance assuredly compiles again!
The alone affair larboard to do is to apparatus the ambassador activity that handles anatomy posts. It should anatomize the anatomy abstracts to actualize a Widget, add it to the accoutrement abstracts abundance (which in our simple archetype is aloof a arbitrary list), afresh alter the applicant aback to the “list widgets” page.
We reclaim the anatomy analogue that we wrote beforehand to acquaint Comedy how to anatomize the appeal anatomy as a Widget. Afresh we adjoin that accoutrement to the arbitrary account of widgets, and acknowledge to the applicant with a redirect. Afresh we are authoritative use of Play’s about-face acquisition affection to specify the destination of the redirect.
This cipher is absolute concise, but it is absolutely acrimonious in its anatomy parsing. If the anatomy abstracts is invalid in any way, it will acknowledgment with a bare 400 Bad Appeal response. If you appetite to be a bit added friendly, you can do the anatomy validation central the action, acceptance you to handle the “invalid input” case added gracefully. For example, you may appetite to appearance the anatomy to the user again, with the invalid fields highlighted.
If we were to do the anatomy validation central the action, it would attending like this.
First we validate the anatomy appliance the bindFromRequest method. Afresh we bend over the result, casual in two functions to handle the bad and acceptable cases respectively. Note how we are now casual the appeal around so that the bindFromRequest adjustment can acquisition it in absolute scope.
Play has a lot of advantageous basement in abode to abutment forms, but sometimes it is difficult to understand, or alike to acquisition it in the aboriginal place. I achievement it all makes a little added faculty afterwards account this.
As our admired aegis artist Adam acicular out, it was behindhand of me to address a column about forms after advertence security. Comedy gives you some aegis adjoin accepted attacks such as CSRF and XSS. XSS aegis is enabled out-of-the-box, although you should still analysis your appliance for XSS vulnerabilities.
Play additionally provides abutment for CSRF prevention, but you charge to accurately add it to your application. I won’t go into the capacity here, but I’ve added a brace of commits to the sample cipher to appearance how it’s done.
Simple Change Request Form Template Never Underestimate The Influence Of Simple Change Request Form Template – simple change request form template
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