Added querydsl tutorial

querydsl/files/FruitFragment.java

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+package org.acme.spring.data.jpa.repo.fruit;
+
+import java.util.List;
+
+import org.acme.spring.data.jpa.model.Fruit;
+
+public interface FruitFragment {
+
+  public List<Fruit> findAllQueryDslName(String name);
+
+  public List<Fruit> findAllQueryDslMaxPriceDesc(Float price);
+
+  public List<Fruit> findAllQueryDslMinPriceAsc(Float price);
+
+  public List<Fruit> findAllQueryDslPriceRange(Float min, Float max);
+
+}

querydsl/files/FruitFragmentImpl.java

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+package org.acme.spring.data.jpa.repo.fruit;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.inject.Inject;
+import javax.persistence.EntityManager;
+
+import org.acme.spring.data.jpa.model.Fruit;
+import org.acme.spring.data.jpa.model.QFruit;
+
+import com.querydsl.jpa.impl.JPAQuery;
+
+public class FruitFragmentImpl implements FruitFragment {
+
+  @Inject
+  EntityManager em;
+
+  @Override
+  public List<Fruit> findAllQueryDslName(String name) {
+
+    QFruit fruit = QFruit.fruit;
+    JPAQuery<Fruit> query = new JPAQuery<Fruit>(this.em);
+    query.from(fruit);
+    if (name != null && !name.isEmpty()) {
+      query.where(fruit.name.eq(name));
+    }
+    return query.orderBy(fruit.name.desc()).fetch();
+  }
+
+  @Override
+  public List<Fruit> findAllQueryDslMaxPriceDesc(Float price) {
+
+    QFruit fruit = QFruit.fruit;
+    JPAQuery<Fruit> query = new JPAQuery<Fruit>(this.em);
+    query.from(fruit);
+    if (price != null && price != 0) {
+      query.where(fruit.price.loe(price));
+    }
+    return query.orderBy(fruit.price.desc()).fetch();
+  }
+
+  @Override
+  public List<Fruit> findAllQueryDslMinPriceAsc(Float price) {
+
+    QFruit fruit = QFruit.fruit;
+    JPAQuery<Fruit> query = new JPAQuery<Fruit>(this.em);
+    query.from(fruit);
+    if (price != null && price != 0) {
+      query.where(fruit.price.goe(price));
+    }
+    return query.orderBy(fruit.price.asc()).fetch();
+  }
+
+  @Override
+  public List<Fruit> findAllQueryDslPriceRange(Float min, Float max) {
+
+    QFruit fruit = QFruit.fruit;
+    JPAQuery<Fruit> query = new JPAQuery<Fruit>(this.em);
+    query.from(fruit);
+    if (min != null && min != 0 && max != null && max != 0) {
+      query.where(fruit.price.between(min, max));
+    }
+    return query.orderBy(fruit.price.desc()).fetch();
+  }
+
+}

querydsl/files/findAllQueryDslFunc.asciidoc

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+Now we can implement Querydsl-queries in the `FruitFragmentImpl`. The class requires a JPA `EntityManager` to interact with the persistent entities, which is passed to the `JPAQuery` constructor when instantiating a query.
+
+In order to define the `Fruit`-entity as the source of the query, we need to create its Q-type first by accessing its static `fruit` field. Then, we can call `query.from(fruit)`.
+
+To retrieve a fruit with a given name, we can use a `where`-clause with the `eq` (equals) operator to get fruits with the name equal to the one passed to the function parameter. Additionally, we can sort the results by name in descending alphabetical order by calling `query.orderBy(fruit.name.desc())` before fetching the result.
+
+public class FruitFragmentImpl implements FruitFragment {
+
+  @Inject
+  EntityManager em;
+
+  @Override
+  public List<Fruit> findAllQueryDslName(String name) {
+
+    JPAQuery<Fruit> query = new JPAQuery<Fruit>(this.em);
+    QFruit fruit = QFruit.fruit;
+    query.from(fruit);
+    if (name != null && !name.isEmpty()) {
+      query.where(fruit.name.eq(name));
+    }
+    return query.orderBy(fruit.name.desc()).fetch();
+  }
+
+We can also get fruits in a given price range by calling `fruit.price.between(min, max)` in the `where`-clause. To see usage of further comparators, see the `findAllQueryDslMaxPriceDesc`and `findAllQueryDslMinPriceAsc` functions.
+
+  @Override
+  public List<Fruit> findAllQueryDslPriceRange(Float min, Float max) {
+  ...
+    if (min != null && min != 0 && max != null && max != 0) {
+      query.where(fruit.price.between(min, max));
+    }
+    return query.orderBy(fruit.price.desc()).fetch();
+  }
+

querydsl/files/function.txt

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+return this.fruitRepository.findAllQueryDslName(name);

querydsl/files/querydsl-annotation-processor.txt

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+        <plugin>
+            <groupId>com.mysema.maven</groupId>
+            <artifactId>apt-maven-plugin</artifactId>
+            <version>1.1.3</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>process</goal>
+                        </goals>
+                            <configuration>
+                                <outputDirectory>target/generated-sources/java</outputDirectory>
+                                    <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor>
+                            </configuration>
+                    </execution>
+                </executions>
+        </plugin>

querydsl/files/querydsl-dependencies.txt

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+        <dependency>
+                <groupId>com.querydsl</groupId>
+                <artifactId>querydsl-apt</artifactId>
+                <version>4.1.3</version>
+                <scope>provided</scope>
+        </dependency>
+        <dependency>
+                <groupId>com.querydsl</groupId>
+                <artifactId>querydsl-jpa</artifactId>
+                <version>4.1.3</version>
+        </dependency>

querydsl/index.asciidoc

@@ -0,0 +1,93 @@
+= Querydsl Tutorial
+====
+This tutorial will teach you how to integrate link:https://querydsl.com/[Querydsl] into a Spring or Quarkus project and how to build Querydsl queries.
+## 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  
+====
+
+[step]
+--
+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.
+[step]
+== Clone QueryDslTutorial repository
+--
+cloneRepository("", "https://github.com/EduardKrieger/QueryDslTutorial.git")
+--
+
+In the next step, integrate Querydsl into your Maven project.
+====
+
+[step]
+== 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.
+[step]
+--
+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.
+
+[step]
+== Create FruitFragment Interface
+--
+createFile("src/main/java/org/acme/spring/data/jpa/repo/fruit/FruitFragment.java","files/FruitFragment.java")
+--
+
+[step]
+== 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> {"})
+--
+
+[step]
+== Implement FruitFragment Interface
+--
+createFile("src/main/java/org/acme/spring/data/jpa/repo/fruit/FruitFragmentImpl.java","files/FruitFragmentImpl.java")
+--
+
+[step]
+== Querying with Querydsl
+--
+displayContent("Querydsl Expressions", [{ "file": "files/findAllQueryDslFunc.asciidoc" }])
+--
+
+[step]
+== 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.
+[step]
+== 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://[[HOST_SUBDOMAIN]]-8080-[[KATACODA_HOST]].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 link:https://querydsl.com/static/querydsl/latest/reference/html_single/[documentation]
+====