Grails Interview Questions

by Sergio del Amo

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GRAILS INTERVIEW QUESTIONS objectcomputing.com/grails

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Sergio del Amo @sdelamo

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objectcomputing.com/grails https://www.ﬂickr.com/photos/42353480@N02/5768808772/sizes/l/ Welcome! Let's talk about your Grails experience

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objectcomputing.com/grails https://www.ﬂickr.com/photos/42353480@N02/5768808772/sizes/l/ Which build tool does Grails use?

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objectcomputing.com/grails BUILD TOOL

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objectcomputing.com/grails Tell me about Grails Scaffolding

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objectcomputing.com/grails Scaffolding is a Grails feature that allows you to quickly generate CRUD interfaces for an existing domain

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objectcomputing.com/grails DYNAMIC SCAFFOLDING dependencies { // ... compile "org.grails.plugins:scaffolding" // ... } build.gradle class Book { String name String about } grails-app/domain class BookController { static scaffold = Book } grails-app/controllers class BookController { static scaffold = true } Old Grails 2.x way

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objectcomputing.com/grails STATIC SCAFFOLDING grails generate-controller Book grails generate-views Book grails generate-all Book Generate a controller and the views for a domain class

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objectcomputing.com/grails Given this scaffolding snippet. Take a look at the use of DELETE. Did not browsers support only GET and POST for forms?

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objectcomputing.com/grails Actually POST is used. DELETE is passed as a parameter named _method.Request gets intercepted by org.grails.web.filters.HiddenHttpMethodFilter.java which wraps the request and uses DELETE AWESOME! +1

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objectcomputing.com/grails Tell me about Grails environments

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objectcomputing.com/grails Grails supports the concepts of development environments by default and will configure itself accordingly when executed.

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objectcomputing.com/grails ENVIRONMENTS environments: development: dataSource: dbCreate: create-drop url: jdbc:h2:mem:devDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE test: dataSource: dbCreate: update url: jdbc:h2:mem:testDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE production: dataSource: dbCreate: none url: jdbc:h2:./prodDb;MVCC=TRUE;LOCK_TIMEOUT=10000;DB_CLOSE_ON_EXIT=FALSE application.yml

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objectcomputing.com/grails CONFIGURATION FILES PER ENVIRONMENT grails-app conf application-production.yml application-development.yml application-test.yml Checkout mrhaki blog post: Using External Configuration files per environment

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objectcomputing.com/grails Execute Gradle tasks per environment ./gradlew -Dgrails.env=prod bootRun

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objectcomputing.com/grails Pass System Properties bootRun { systemProperties System.properties } integrationTest { systemProperties System.properties }

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objectcomputing.com/grails Do you know what the acronym ORM stands for?

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objectcomputing.com/grails Stands for Object-Relational Mapping. That it is to say: Mapping classes onto a relational database layer

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objectcomputing.com/grails In GRAILS we normally use GORM. A data access toolkit which provides a rich set of APIs for accessing relational and non-relational data

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objectcomputing.com/grails Which GORM implementations do you know about?

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objectcomputing.com/grails GORM Implementations

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objectcomputing.com/grails In the previous scaffolding code I found this method: def index(Integer max) { params.max = Math.min(max ?: 10, 100) respond Book.list(params), model:[bookCount: Book.count()] } I have not defined list() or count() methods. What is going on?

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objectcomputing.com/grails Those are Dynamic Finders. A dynamic finder looks like a static method invocation, but the methods themselves don’t actually exists in any form at the code level. Instead, a method is generated for us based on the properties of a given class.

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objectcomputing.com/grails Do you know what a derived property is?

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objectcomputing.com/grails A derived property is one that takes its value from a SQL expression, often but not necessarily based on the value of one or more persistent properties

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objectcomputing.com/grails What about using a transient instead the derived property?

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objectcomputing.com/grails With a derived property you have the ability to do queries such as: Product.findAllByTaxGreaterThan(21.12) The drawback of derived queries is that you may give some database portability

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objectcomputing.com/grails In Grails applications you don’t see a lot of try / catch block. Why?

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objectcomputing.com/grails Groovy translates all exceptions into runtime exceptions, so Groovy code is never forced to catch an exception

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objectcomputing.com/grails Any area of Grails development where the distinction Checked and Unchecked exceptions is important?

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objectcomputing.com/grails Transactional methods get an automatic rollback if a method throws a runtime exception. Checked exceptions do NOT rollback transactions

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objectcomputing.com/grails I am developing a Grails application to organise my agenda. I have a domain class: class AgendaEvent { String eventName Date eventDate } I want to restrict the application to enter only upcoming dates. Could you help me?

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objectcomputing.com/grails No problem! A Grails domain class can express constraints simply by defining a static property named constraints, that has a closure as a value

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objectcomputing.com/grails Constraints - Custom validator

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objectcomputing.com/grails Any other area of Grails where you can often use validators?

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objectcomputing.com/grails Yes, Command Objects and URLMappings

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objectcomputing.com/grails I wrote a test with for your validator. Do you see any problem with it?

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objectcomputing.com/grails Replace validate() with no args with validate with a List of properties which are under test. Thus, you test eventDate on isolation without the need to provide valid values for other properties

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objectcomputing.com/grails I personally would use a where block in your Spock test.

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objectcomputing.com/grails In a Grails Controller, I have such an action: Do you see any problems?

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objectcomputing.com/grails Params object has a number of convenience methods for boolean, long, char, short …

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objectcomputing.com/grails You could use the parameters as action method arguments. If you provide wrong types default values will be binded. e.g. null, false

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objectcomputing.com/grails However, the best approach would probably be to use a Command Object.

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objectcomputing.com/grails I want to display the last five books entered into the system. What do you think?

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grails-app/controllers/demo/BookController.groovy

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grails-app/conf/application.yml

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encapsulate your business logic in Grails services grails-app/services/demo/BookService.groovy

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grails-app/views/book/latestBooks.gsp

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objectcomputing.com/grails Why are you getting the configuration values implementing GrailsConfigurationAware instead of using grailsApplication?

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objectcomputing.com/grails It is not ideal because the application is paying the performance price of retrieving the config value every time the service method is invoked. Services are singletons by default. void setConfiguration(Config co) will be called just once

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objectcomputing.com/grails Could you write the service with a where query instead?

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grails-app/services/demo/BookService.groovy

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•Use DetachedCriteria •Compile time type checked •Compatible with static compilation •Use raw Groovy for criteria •Are compose-able WHERE QUERIES

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objectcomputing.com/grails I want to restrict the invocations of a controller’s action to DELETE requests. I plan to create an interceptor and reject any request with a HTTP verb other than DELETE. What do you think?

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objectcomputing.com/grails It is much easier! You should use Grails allowedMethods property in your controller!

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objectcomputing.com/grails Do you know how to create a multi-project build with Grails 3?

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objectcomputing.com/grails WHAT ABOUT MULTI-PROJECT dependencies { // ... compile project(“:myplugin”) // ... } myapi/build.gradle grails create-app myapi —profile=rest-api grails create-plugin myplugin --profile=plugin CREATE AN APP AND A PLUGIN include 'myapi', 'myplugin' settings.gradle

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objectcomputing.com/grails Can you tell me about Grails profiles?

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•angular - A profile for creating applications using AngularJS •rest-api - Profile for REST API applications •base - The base profile extended by other profiles •angular2 - A profile for creating Grails applications with Angular 2 •plugin - Profile for plugins designed to work across all profiles •profile - A profile for creating new Grails profiles •react - A profile for creating Grails applications with a React frontend •rest-api-plugin - Profile for REST API plugins •web - Profile for Web applications •web-jboss7 - A Profile for Creating a JBoss 7.1 EAP Project •web-plugin - Profile for Plugins designed for Web applications •webpack - A profile for creating applications with node-based frontends using webpack

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objectcomputing.com/grails What would you upgrade an app from Grails 3.2.6 to 3.2.8?

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objectcomputing.com/grails I would checkout the release notes in grails.org Normally it involves increasing a version number in gradle.properties I would diff two apps created from scratch with each version? Or use a https://github.com/erichelgeson/ grails-versions

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objectcomputing.com/grails How do you keep learning about Grails?

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objectcomputing.com/grails I checkout every Monday guides.grails.org

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objectcomputing.com/grails I am subscribed to GroovyCalamari.com

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objectcomputing.com/grails Do you know how to get commercial support for Grails?

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objectcomputing.com/grails OCI is HOME TO GRAILS

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YOU’RE HIRED

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