Use Criteria Queries in a Spring Data Application (#5014)

* Use Criteria Queries in a Spring Data Application

* formatting fix

* making the workflow more readable

persistence-modules/spring-jpa/src/main/java/org/baeldung/persistence/criteria/dao/BookRepositoryImpl.java

@@ -0,0 +1,46 @@
+package org.baeldung.persistence.criteria.dao;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.persistence.EntityManager;
+import javax.persistence.TypedQuery;
+import javax.persistence.criteria.CriteriaBuilder;
+import javax.persistence.criteria.CriteriaQuery;
+import javax.persistence.criteria.Predicate;
+import javax.persistence.criteria.Root;
+
+import org.baeldung.persistence.criteria.model.Book;
+import org.baeldung.persistence.criteria.repository.BookRepositoryCustom;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public class BookRepositoryImpl implements BookRepositoryCustom {
+
+    private EntityManager em;
+
+    public BookRepositoryImpl(EntityManager em) {
+        this.em = em;
+    }
+
+    @Override
+    public List<Book> findBooksByAuthorNameAndTitle(String authorName, String title) {
+        CriteriaBuilder cb = em.getCriteriaBuilder();
+        CriteriaQuery<Book> cq = cb.createQuery(Book.class);
+
+        Root<Book> book = cq.from(Book.class);
+        List<Predicate> predicates = new ArrayList<>();
+
+        if (authorName != null) {
+            predicates.add(cb.equal(book.get("author"), authorName));
+        }
+        if (title != null) {
+            predicates.add(cb.like(book.get("title"), "%" + title + "%"));
+        }
+        cq.where(predicates.toArray(new Predicate[0]));
+
+        TypedQuery<Book> query = em.createQuery(cq);
+        return query.getResultList();
+    }
+
+}

persistence-modules/spring-jpa/src/main/java/org/baeldung/persistence/criteria/model/Book.java

@@ -0,0 +1,36 @@
+package org.baeldung.persistence.criteria.model;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+
+@Entity
+public class Book {
+
+    @Id
+    private Long id;
+
+    private String title;
+
+    private String author;
+
+    public Long getId() {
+        return id;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getAuthor() {
+        return author;
+    }
+
+    public void setAuthor(String author) {
+        this.author = author;
+    }
+
+}

persistence-modules/spring-jpa/src/main/java/org/baeldung/persistence/criteria/repository/BookRepository.java

@@ -0,0 +1,9 @@
+package org.baeldung.persistence.criteria.repository;
+
+import org.baeldung.persistence.criteria.model.Book;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
+
+public interface BookRepository extends JpaRepository<Book, Long>, BookRepositoryCustom, JpaSpecificationExecutor<Book> {
+
+}

persistence-modules/spring-jpa/src/main/java/org/baeldung/persistence/criteria/repository/BookRepositoryCustom.java

@@ -0,0 +1,11 @@
+package org.baeldung.persistence.criteria.repository;
+
+import java.util.List;
+
+import org.baeldung.persistence.criteria.model.Book;
+
+public interface BookRepositoryCustom {
+
+    List<Book> findBooksByAuthorNameAndTitle(String authorName, String title);
+    
+}

persistence-modules/spring-jpa/src/main/java/org/baeldung/persistence/criteria/repository/BookService.java

@@ -0,0 +1,25 @@
+package org.baeldung.persistence.criteria.repository;
+
+import static org.baeldung.persistence.criteria.repository.BookSpecifications.hasAuthor;
+import static org.baeldung.persistence.criteria.repository.BookSpecifications.titleContains;
+import static org.springframework.data.jpa.domain.Specifications.where;
+
+import java.util.List;
+
+import org.baeldung.persistence.criteria.model.Book;
+import org.springframework.stereotype.Service;
+
+@Service
+public class BookService {
+
+    private BookRepository bookRepository;
+
+    public BookService(BookRepository bookRepository) {
+        this.bookRepository = bookRepository;
+    }
+
+    public List<Book> query(String author, String title) {
+        return bookRepository.findAll(where(hasAuthor(author)).and(titleContains(title)));
+    }
+
+}

persistence-modules/spring-jpa/src/main/java/org/baeldung/persistence/criteria/repository/BookSpecifications.java

@@ -0,0 +1,16 @@
+package org.baeldung.persistence.criteria.repository;
+
+import org.baeldung.persistence.criteria.model.Book;
+import org.springframework.data.jpa.domain.Specification;
+
+public class BookSpecifications {
+
+    public static Specification<Book> hasAuthor(String author) {
+        return (book, cq, cb) -> cb.equal(book.get("author"), author);
+    }
+
+    public static Specification<Book> titleContains(String title) {
+        return (book, cq, cb) -> cb.like(book.get("title"), "%" + title + "%");
+    }
+
+}