Grails Interview Questions

Talk at Greach 2017

Transcript

1. GRAILS INTERVIEW QUESTIONS
   objectcomputing.com/grails
   

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2. Sergio del Amo
   @sdelamo
   

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

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5. objectcomputing.com/grails
   BUILD TOOL
   

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6. objectcomputing.com/grails
   Tell me about
   Grails Scaffolding
   

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

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8. 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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9. 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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10. 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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11. 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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12. objectcomputing.com/grails
    Tell me about Grails
    environments
    

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

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14. 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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15. 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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16. objectcomputing.com/grails
    Execute Gradle tasks per environment
    ./gradlew -Dgrails.env=prod bootRun
    

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

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

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

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

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22. objectcomputing.com/grails
    GORM Implementations
    

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23. 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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24. 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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25. objectcomputing.com/grails
    Do you know what a
    derived property is?
    

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

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

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

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

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32. 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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33. 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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34. 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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35. objectcomputing.com/grails
    Constraints - Custom validator
    

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

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37. objectcomputing.com/grails
    Yes, Command Objects
    and URLMappings
    

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

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

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

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

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

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

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46. grails-app/controllers/demo/BookController.groovy
    

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47. grails-app/conf/application.yml
    

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

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49. grails-app/views/book/latestBooks.gsp
    

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

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

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53. grails-app/services/demo/BookService.groovy
    

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

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

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

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

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

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

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

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

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

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67. objectcomputing.com/grails
    OCI is HOME TO GRAILS
    

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68. YOU’RE HIRED
    

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69. ?
    

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70. OCI
    12140 Woodcrest Exec. Dr., Ste. 250
    Saint Louis, MO 63141 USA
    © 2017, All Rights Reserved.
    No part of this publication may be photocopied or reproduced in any form without written permission
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    While every precaution has been taken in preparing this material, including research, development and
    testing, OCI assumes no responsibility for errors or omissions. No liability is assumed by OCI for any
    damages resulting from the use of this information.
    

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