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Querydsl Tutorial

Prerequisites

  • Installed devonfw IDE

  • User should have basic Java development experience

Learning goals.

Here in this tutorial you will learn * To integrate Querydsl in your project * To build Querydsl expressions

restoreDevonfwIde(["java","mvn"])

devonfw IDE has been installed for you.

First, clone the QueryDslTutorial repository from GitHub. It contains an application with a simple REST service.

Clone QueryDslTutorial repository

In the next step, integrate Querydsl into your Maven project.

== Add Querydsl dependencies to Maven Project

changeFile("QueryDslTutorial/pom.xml" , {"file": "files/querydsl-dependencies.txt", "placeholder": "<QueryDslDependencies>"}) changeFile("QueryDslTutorial/pom.xml" , {"file": "files/querydsl-annotation-processor.txt", "placeholder": "<AnnotationProcessor>"})

Next, navigate to the devonfw/QueryDslTutorial directory.

changeWorkspace("devonfw/workspaces/main/QueryDslTutorial")

The data model consists of a Fruit entity with Id, name, color, and price fields.

To extend the application with custom queries in Querydsl, we need to create a FruitFragment-interface and its implementation. This will be extended by the FruitRepository along with the CrudRepository.

== Create FruitFragment Interface

createFile("src/main/java/org/acme/spring/data/jpa/repo/fruit/FruitFragment.java","files/FruitFragment.java")

== Extend FruitRepository with FruitFragment Interface

changeFile("src/main/java/org/acme/spring/data/jpa/repo/fruit/FruitRepository.java", {"content": "public interface FruitRepository extends CrudRepository<Fruit, Long>, FruitFragment {", "placeholder": "public interface FruitRepository extends CrudRepository<Fruit, Long> {"})

== Implement FruitFragment Interface

createFile("src/main/java/org/acme/spring/data/jpa/repo/fruit/FruitFragmentImpl.java","files/FruitFragmentImpl.java")

== Querying with Querydsl

displayContent("Querydsl Expressions", [{ "file": "files/findAllQueryDslFunc.asciidoc" }])

== Implement GET-Request in FruitResource

changeFile("src/main/java/org/acme/spring/data/jpa/repo/fruit/FruitResource.java", {"placeholder": "return null;", "file": "files/function.txt"})

Now you can run the application in development mode.

Run Application

executeCommand("mvn compile quarkus:dev", "mvn compile quarkus:dev")

Accessing the application with the following link will send a GET-request for fruits named Cherry. The FruitResource will call the FindByName method and pass the name parameter to the FruitRepository’s `findAllQueryDslName method, which it inherents from the FruitFragment interface. The querying occurs in the method’s implementation, as explained in step 6. https://-8080-.environments.katacoda.com/fruits/name/Cherry

Conclusion

To summarize, we learned how to integrate Querydsl into your Maven project and querying with Querydsl. For more information on queries, visit the Querydsl documentation