SpringQuickPoll

Part 1 - Domain Implementation

• Domain objects are the backbone for an application and contain the business logic.
• Create a sub package of io.zipcoder.tc_spring_poll_application named domain.

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Part 1.1 - Create class Option

• Create an Option class in the domain sub-package.
• Option class signature is annotated with @Entity

• Option has an id instance variable of type Long

  • id should be annotated with
    • @Id
      • denotes primary key of this entity
    • @GeneratedValue
      • configures the way of increment of the specified column(field)
    • @Column(name = "OPTION_ID")
      • specifies mapped column for a persistent property or field

• Option has a value instance variable of type String

  • value should be annotated with
    • @Column(name = "OPTION_VALUE")

• Create a getter and setter for each of the respective instance variables.

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Part 1.2 - Create class Poll

• Create a Poll class in the domain sub-package.
• Poll class signature is annotated with @Entity

• Poll has an id instance variable of type Long

  • id should be annotated with
    • @Id
    • @GeneratedValue
    • Column(name = "POLL_ID")

• Poll has a question instance variable of type String

  • question should be annotated with
    • @Column(name = "QUESTION")

• Poll has an options instance variable of type Set of Option

  • options should be annotated with
    • @OneToMany(cascade = CascadeType.ALL)
    • @JoinColumn(name = "POLL_ID")
    • @OrderBy

• Create a getter and setter for each of the respective instance variables.

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Part 1.3 - Create class Vote

• Create a Vote class in the domain sub-package.
• Vote class signature is annotated with @Entity

• Vote has an id instance variable of type Long

  • id should be annotated with
    • @Id
    • @GeneratedValue
    • Column(name = "VOTE_ID")

• Vote has a option instance variable of type Option

  • option should be annotated with
    • @Column(name = "OPTION_ID")

• Create a getter and setter for each of the respective instance variables.

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Part 2 - Repository Implementation

• Repositories or Data Access Objects (DAO), provide an abstraction for interacting with datastores.
• Typically DAOs include an interface that provides a set of finder methods such as findById, findAll, for retrieving data, and methods to persist and delete data.
• It is customary to have one Repository per domain object.
• Create a sub-package of io.zipcoder.tc_spring_poll_application named repositories.

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Part 2.1 - Create interface OptionRepository

• Create an OptionRepository interface in the repositories subpackage.
• OptionRepository extends CrudRepository<Option, Long>

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Part 2.2 - Create interface PollRepository

• Create a PollRepository interface in the repositories subpackage.
• PollRepository extends CrudRepository<Poll, Long>

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Part 2.3 - Create interface VoteRepository

• Create a VoteRepository interface in the repositories subpackage.
• VoteRepository extends CrudRepository<Vote, Long>

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Part 3 - Controller Implementation

• Controllers provides all of the necessary endpoints to access and manipulate respective domain objects.
  • REST resources are identified using URI endpoints.
• Create a sub package of io.zipcoder.tc_spring_poll_application named controller.

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Part 3.1 - Create class PollController

• Create a PollController class in the controller sub package.

  • PollController signature should be annotated with @RestController

• PollController has a pollRepository instance variable of type PollRepository

  • pollRepository should be annotated with @Inject

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Part 3.1.1 - Create GET request method

• The method definition below supplies a GET request on the /polls endpoint which provides a collection of all of the polls available in the QuickPolls application. Copy and paste this into your PollController class.

@RequestMapping(value="/polls", method= RequestMethod.GET)
public ResponseEntity<Iterable<Poll>> getAllPolls() {
    Iterable<Poll> allPolls = pollRepository.findAll();
    return new ResponseEntity<>(allPolls, HttpStatus.OK);
}

• The method above begins with reading all of the polls using the PollRepository.
• We then create an instance of ResponseEntity and pass in Poll data and the HttpStatus.OK status value.
• The Poll data becomes part of the response body and OK (code 200) becomes the response status code.

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Part 3.1.2 - Testing via Postman

• Ensure that the start-class tag in your pom.xml encapsulates io.zipcoder.springdemo.QuickPollApplication
• Open a command line and navigate to the project's root directory and run this command:
  • mvn spring-boot:run
• Launch the Postman app in your Chrome browser and enter the URL http://localhost:8080/polls and hit Send.
• Because we don’t have any polls created yet, this command should result in an empty collection.

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Part 3.1.3 - Create POST request method

• We accomplish the capability to add new polls to the PollController by implementing the POST verb functionality in a createPoll method:

@RequestMapping(value="/polls", method=RequestMethod.POST)
public ResponseEntity<?> createPoll(@RequestBody Poll poll) {
        poll = pollRepository.save(poll);
        return new ResponseEntity<>(null, HttpStatus.CREATED);
}

• Take note that the method
  • has a parameter of type @RequestBody Poll poll
    • @RequestBody tells Spring that the entire request body needs to be converted to an instance of Poll
  • delegates the Poll persistence to PollRepository’s save method
    • poll = pollRepository.save(poll);

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Part 3.1.4 - Modify createPoll

• Best practice is to convey the URI to the newly created resource using the Location HTTP header via Spring's ServletUriComponentsBuilder utility class. This will ensure that the client has some way of knowing the URI of the newly created Poll.

URI newPollUri = ServletUriComponentsBuilder
	.fromCurrentRequest()
	.path("/{id}")
	.buildAndExpand(poll.getId())
	.toUri();

• Modify the createPoll method so that it returns a ResponseEntity which takes an argument of a new HttpHeaders() whose location has been set to the above newPollUri via the setLocation method.

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Part 3.1.5 - Create GET request method

• The code snippet below enables us to access an individual poll.
• The value attribute in the @RequestMapping takes a URI template /polls/{pollId}.
• The placeholder {pollId} along with @PathVarible annotation allows Spring to examine the request URI path and extract the pollId parameter value.
• Inside the method, we use the PollRepository’s findOne finder method to read the poll and pass it as part of a ResponseEntity.

@RequestMapping(value="/polls/{pollId}", method=RequestMethod.GET)
public ResponseEntity<?> getPoll(@PathVariable Long pollId) {
	Poll p = pollRepository.findOne(pollId);
	return new ResponseEntity<> (p, HttpStatus.OK);
}

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Part 3.1.6 - Create UPDATE request method

• The code snippet below enables us to update a poll.

RequestMapping(value="/polls/{pollId}", method=RequestMethod.PUT)
public ResponseEntity<?> updatePoll(@RequestBody Poll poll, @PathVariable Long pollId) {
        // Save the entity
        Poll p = pollRepository.save(poll);
        return new ResponseEntity<>(HttpStatus.OK);
}

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Part 3.1.7 - Create DELETE request method.

• The code snippet below enables us to delete a poll.

@RequestMapping(value="/polls/{pollId}", method=RequestMethod.DELETE)
public ResponseEntity<?> deletePoll(@PathVariable Long pollId) {
        pollRepository.delete(pollId);
        return new ResponseEntity<>(HttpStatus.OK);
}

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Part 3.1.8 - Test

• Restart the QuickPoll application.
• Use Postman to execute a PUT to http://localhost:8080/polls/1 whose request body is the JSON object below.
• You can modify the request body in Postman by navigating to the Body tab, selecting the raw radio button, and selecting the JSON option from the text format dropdown.

{
    "id": 1,
        "question": "What's the best netflix original?",
        "options": [
	    { "id": 1, "value": "Black Mirror" },
	    { "id": 2, "value": "Stranger Things" },
	    { "id": 3, "value": "Orange is the New Black"},
	    { "id": 4, "value": "The Get Down" }
	]
}

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Part 3.2 - Create class VoteController

• Following the principles used to create PollController, we implement the VoteController class.
• Below is the code for the VoteController class along with the functionality to create a vote.
• The VoteController uses an injected instance of VoteRepository to perform CRUD operations on Vote instances.

@RestController
public class VoteController {
    @Inject
    private VoteRepository voteRepository;

    @RequestMapping(value = "/polls/{pollId}/votes", method = RequestMethod.POST)
    public ResponseEntity<?> createVote(@PathVariable Long pollId, @RequestBody Vote
            vote) {
        vote = voteRepository.save(vote);
        // Set the headers for the newly created resource
        HttpHeaders responseHeaders = new HttpHeaders();
        responseHeaders.setLocation(ServletUriComponentsBuilder.
                fromCurrentRequest().path("/{id}").buildAndExpand(vote.getId()).toUri());
        return new ResponseEntity<>(null, responseHeaders, HttpStatus.CREATED);
    }
}

Part 3.2.1 - Testing VoteController

• To test the voting capabilities, POST a new Vote to the /polls/1/votes endpoint with the option object expressed in JSON below.
• On successful request execution, you will see a Location response header with value http://localhost:8080/polls/1/votes/1.

{
    "option": { "id": 1, "value": "Black Mirror" }
}

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Part 3.2.2 - Modify VoteRepository

• The method findAll in the VoteRepository retrieves all votes in a Database rather than a given poll.
• To ensure we can get votes for a given poll, we must add the code below to our VoteRepository.

public interface VoteRepository extends CrudRepository<Vote, Long> {
    @Query(value = "SELECT v.* " +
            "FROM Option o, Vote v " +
            "WHERE o.POLL_ID = ?1 " +
            "AND v.OPTION_ID = o.OPTION_ID", nativeQuery = true)
    public Iterable<Vote> findVotesByPoll(Long pollId);
}

• The custom finder method findVotesByPoll takes the ID of the Poll as its parameter.
• The @Query annotation on this method takes a native SQL query along with the nativeQuery flag set to true.
• At runtime, Spring Data JPA replaces the ?1 placeholder with the passed-in pollId parameter value.

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Part 3.2.3 - Modify VoteController

• Create a getAllVotes method in the VoteController

@RequestMapping(value="/polls/{pollId}/votes", method=RequestMethod.GET)
public Iterable<Vote> getAllVotes(@PathVariable Long pollId) {
        return voteRepository. findByPoll(pollId);
}

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Part 4 - Data Transfer Object (DTO) Implementation

• The final piece remaining for us is the implementation of the ComputeResult resource.
• Because we don’t have any domain objects that can directly help generate this resource representation, we implement two Data Transfer Objects or DTOs—OptionCount and VoteResult
• Create a sub package of java named dtos

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Part 4.1 - Create class OptionCount

• The OptionCount DTO contains the ID of the option and a count of votes casted for that option.

public class OptionCount {
    private Long optionId;
    private int count;

    public Long getOptionId() {
        return optionId;
    }

    public void setOptionId(Long optionId) {
        this.optionId = optionId;
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }
}

Part 4.2 - Create class VoteResult

• The VoteResult DTO contains the total votes cast and a collection of OptionCount instances.

import java.util.Collection;
public class VoteResult {
    private int totalVotes;
    private Collection<OptionCount> results;

    public int getTotalVotes() {
        return totalVotes;
    }

    public void setTotalVotes(int totalVotes) {
        this.totalVotes = totalVotes;
    }

    public Collection<OptionCount> getResults() {
        return results;
    }

    public void setResults(Collection<OptionCount> results) {
        this.results = results;
    }
}

Part 4.3 - Create class ComputeResultController

• Following the principles used in creating the PollController and VoteController, we create a new ComputeResultController class

@RestController
public class ComputeResultController {
    @Inject
    private VoteRepository voteRepository;

    @RequestMapping(value = "/computeresult", method = RequestMethod.GET)
    public ResponseEntity<?> computeResult(@RequestParam Long pollId) {
        VoteResult voteResult = new VoteResult();
        Iterable<Vote> allVotes = voteRepository.findVotesByPoll(pollId);

        // Algorithm to count votes
        return new ResponseEntity<VoteResult>(voteResult, HttpStatus.OK);
    }

• We inject an instance of VoteRepository into the controller, which is used to retrieve votes for a given poll.
• The computeResult method takes pollId as its parameter.
• The @RequestParam annotation instructs Spring to retrieve the pollId value from a HTTP query parameter.
• The computed results are sent to the client using a newly created instance of ResponseEntity.

Part 4.4 - Test via Postman

• Start/restart the QuickPoll application.
• Using the earlier Postman requests, create a poll and cast votes on its options.
• Ensure a JSON file with a status of 200 is returned by executing a GET request of http://localhost:8080/computeresults?pollId=1 via Postman