{"id":93,"date":"2019-11-16T23:12:08","date_gmt":"2019-11-16T23:12:08","guid":{"rendered":"https:\/\/www.kindsonthegenius.com\/microservices\/?p=93"},"modified":"2019-11-17T16:39:48","modified_gmt":"2019-11-17T16:39:48","slug":"cqrs-with-axon-tutorial-part-6-build-the-summary-projection","status":"publish","type":"post","link":"https:\/\/www.kindsonthegenius.com\/microservices\/cqrs-with-axon-tutorial-part-6-build-the-summary-projection\/","title":{"rendered":"CQRS With Axon Tutorial: Part 6 \u2013 Build the Summary Projection"},"content":{"rendered":"

In this part we would create the summary projection class.This class would be part of the query package.<\/p>\n

This is would be a spring bean (annotated with @Component annotation) and would be responsible for handle persistence. So it would be able to saved data. Also, it should retrieve data from the database to be displayed on the grid in the GUI.<\/p>\n

 <\/p>\n

Follow the 14 steps given below:<\/p>\n

Step 1:<\/strong> Create a java class in the query package. Name it SummaryProjection<\/p>\n

Step 2:<\/strong> Annotate the class with the @Component annotation<\/p>\n

Step 3:<\/strong> Add a final private variable of type EntityManager<\/p>\n

Step 4:<\/strong> Add a constructor and inject the EntityManager variable<\/p>\n

The code for step 3 and 4 is shown below<\/p>\n

 <\/p>\n

private<\/span> final<\/span> EntityManager entityManager;<\/span>\r\n\r\npublic<\/span> SummaryProjection<\/span>(<\/span>EntityManager entityManager)<\/span> {<\/span>\r\n    this<\/span>.<\/span>entityManager<\/span> =<\/span> entityManager;<\/span>\r\n}<\/span>\r\n<\/pre>\n
 <\/p>\n
Step 5:<\/strong> Create event handlers for the IssuedEvent() and RedeemedEvent()<\/p>\n
Step 6<\/strong>: Create Query handler to return a list of card summaries<\/p>\n
Step 7:<\/strong> Create a Query handler for handling the SizeQuery<\/p>\n
 <\/p>\n
At this point, the four methods will be as shown below:<\/p>\n
@EventHandler<\/span>\r\npublic<\/span> void<\/span> handle<\/span>(<\/span>IssuedEvent evt)<\/span> {<\/span>\r\n\r\n}<\/span>\r\n\r\n@EventHandler<\/span>\r\npublic<\/span> void<\/span> handle<\/span>(<\/span>RedeemedEvent evt)<\/span> {<\/span>\r\n\r\n}<\/span>\r\n\r\n@QueryHandler<\/span>\r\npublic<\/span> List<<\/span>CardSummary><\/span> handle<\/span>(<\/span>DataQuery query){<\/span>\r\n\r\n}<\/span>\r\n\r\n@QueryHandler<\/span>\r\npublic<\/span> Integer handle<\/span>(<\/span>SizeQuery query)<\/span> {<\/span>\r\n\r\n}<\/span>\r\n<\/pre>\n
 <\/p>\n
Step 8:<\/strong> For the IssuedEvent, you need to create and persist a new entity. The code is shown below:<\/p>\n
entityManager.<\/span>persist<\/span>(<\/span>new<\/span> CardSummary(<\/span>\r\n        evt.<\/span>getId<\/span>(),<\/span>\r\n        evt.<\/span>getAmount<\/span>(),<\/span>\r\n        evt.<\/span>getAmount<\/span>()<\/span>\r\n));<\/span>\r\n<\/pre>\n
 <\/p>\n
Step 9:<\/strong> For the RedeemedEvent, you need to first find the CardSummary and then update it’s balance. The code is shown below<\/p>\n
CardSummary summary =<\/span> entityManager.<\/span>find<\/span>(<\/span>CardSummary.<\/span>class<\/span>,<\/span>\r\n        evt.<\/span>getId<\/span>());<\/span>\r\nsummary.<\/span>setRemainingBalance<\/span>(<\/span>summary.<\/span>getRemainingBalance<\/span>()<\/span>\r\n-<\/span>evt.<\/span>getAmount<\/span>());<\/span>\r\n<\/pre>\n
 <\/p>\n
Step 10:<\/strong> Configure TrackingEventProcessor. You do this by creating an empty config method. It takes EventProcessingConfiguration as parameter.<\/p>\n
Step 11:<\/strong> Annotate this method with @Autowired annotation<\/p>\n
The code is given below:<\/p>\n
<\/p>\n
\/\/Configure Tracking Event<\/span>\r\n@Autowired<\/span>\r\npublic<\/span> void<\/span> config<\/span>(<\/span>EventProcessingConfiguration config)<\/span> {<\/span>\r\n    \r\n}<\/span>\r\n<\/pre>\n
 <\/p>\n
Step 12:<\/strong> For the List QueryHandler, you need to create a query that returns a List<CardSummary> using the create() query method of the entityManager. The code is given below:<\/p>\n
return<\/span> entityManager\r\n       .<\/span>createQuery<\/span>(<\/span>\"SELECT c FROM CardSummary c ORDER BY c.id\"<\/span>,<\/span>\r\n               CardSummary.<\/span>class<\/span>)<\/span>\r\n        .<\/span>getResultList<\/span>();<\/span>\r\n<\/pre>\n
 <\/p>\n
Step 13:<\/strong> For the QueryHandler for SizeQuery,\u00a0 it would be similar to step 12. But this time write a query to return count..See code below<\/p>\n
<\/p>\n
return<\/span> entityManager\r\n        .<\/span>createQuery<\/span>(<\/span>\"SELECT COUNT(c) FROM CardSummary c\"<\/span>,<\/span>\r\n                Long.<\/span>class<\/span>)<\/span>\r\n        .<\/span>getSingleResult<\/span>()<\/span>\r\n        .<\/span>intValue<\/span>();<\/span>\r\n<\/pre>\n
 <\/p>\n
At this point we are done with the summary projection and now we need to worry about getting the data into the grid in the GUI.<\/p>\n
Step 14:<\/strong> Run the application. Also start the axonserver. Test to make sure everything works fine.<\/p>\n
 <\/p>\n
Just for review, I’m putting the complete code for the SummaryProjection class below. However, I recommend you type it out by yourself. In that way you improve your skills in CQRS with AxonFramework.<\/p>\n
 <\/p>\n
@Component<\/span>\r\npublic<\/span> class<\/span> SummaryProjection<\/span> {<\/span>\r\n\r\n    private<\/span> final<\/span> EntityManager entityManager;<\/span>\r\n\r\n    public<\/span> SummaryProjection<\/span>(<\/span>EntityManager entityManager)<\/span> {<\/span>\r\n\r\n        this<\/span>.<\/span>entityManager<\/span> =<\/span> entityManager;<\/span>\r\n    }<\/span>\r\n\r\n    @EventHandler<\/span>\r\n    public<\/span> void<\/span> on<\/span>(<\/span>IssuedEvt evt)<\/span> {<\/span>\r\n        entityManager.<\/span>persist<\/span>(<\/span>new<\/span> CardSummary(<\/span>\r\n                evt.<\/span>getId<\/span>(),<\/span>\r\n                evt.<\/span>getAmount<\/span>(),<\/span>\r\n                evt.<\/span>getAmount<\/span>()<\/span>\r\n        ));<\/span>\r\n    }<\/span>\r\n\r\n    @EventHandler<\/span>\r\n    public<\/span> void<\/span> on<\/span>(<\/span>RedeemedEvt evt)<\/span> {<\/span>\r\n        CardSummary summary =<\/span> entityManager.<\/span>find<\/span>(<\/span>CardSummary.<\/span>class<\/span>,<\/span>\r\n                evt.<\/span>getId<\/span>());<\/span>\r\n        summary.<\/span>setRemainingBalance<\/span>(<\/span>summary.<\/span>getRemainingBalance<\/span>()<\/span>\r\n        -<\/span> evt.<\/span>getAmount<\/span>());<\/span>\r\n    }<\/span>\r\n\r\n    \/\/Configuring tracking event processor<\/span>\r\n    @Autowired<\/span>\r\n    public<\/span> void<\/span> config<\/span>(<\/span>EventProcessingConfiguration config)<\/span> {<\/span>\r\n       \/\/ config.eventProcessor(getClass().getPackage().getName());<\/span>\r\n    }<\/span>\r\n\r\n    @QueryHandler<\/span>\r\n    public<\/span> List<<\/span>CardSummary><\/span> handle<\/span>(<\/span>DataQuery query)<\/span> {<\/span>\r\n        return<\/span> entityManager\r\n                .<\/span>createQuery<\/span>(<\/span>\"SELECT c FROM CardSummary c ORDER BY c.id\"<\/span>,<\/span>\r\n                        CardSummary.<\/span>class<\/span>)<\/span>\r\n                .<\/span>getResultList<\/span>();<\/span>\r\n    }<\/span>\r\n\r\n    @QueryHandler<\/span>\r\n    public<\/span> Integer handle<\/span>(<\/span>SizeQuery query)<\/span> {<\/span>\r\n        return<\/span> entityManager\r\n                .<\/span>createQuery<\/span>(<\/span>\"SELECT COUNT(c) FROM CardSummary c\"<\/span>,<\/span>\r\n                        Long.<\/span>class<\/span>)<\/span>\r\n                .<\/span>getSingleResult<\/span>()<\/span>\r\n                .<\/span>intValue<\/span>();<\/span>\r\n    }<\/span>\r\n}<\/span>\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
In this part we would create the summary projection class.This class would be part of the query package. This is would be a spring bean … <\/p>\n","protected":false},"author":1,"featured_media":94,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12,27],"tags":[34,35],"class_list":["post-93","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-axon","category-axonframework","tag-summaryprojection","tag-trackingeventprocessor"],"_links":{"self":[{"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/posts\/93","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/comments?post=93"}],"version-history":[{"count":3,"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/posts\/93\/revisions"}],"predecessor-version":[{"id":98,"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/posts\/93\/revisions\/98"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/media\/94"}],"wp:attachment":[{"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/media?parent=93"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/categories?post=93"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.kindsonthegenius.com\/microservices\/wp-json\/wp\/v2\/tags?post=93"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}