Dependencies, Entity Classes, and Configuration for Jinq to Create Database Queries in Java

Jinq is a library that provides support for database queries in Java. It is inspired by .NET’s LINQ. A developer can use Java Stream API, standard functions (e.g. , ), and relational, arithmetic and logical operators (e.g. ==, books = jinqDataProvider.streamAll(entityManager, Book.class) .where(book -> book.getPages() > && book.isPublished()).toList(); 50 In this example, the is not a generated metamodel but a JPA entity class. It looks like magic. Under the hood, Jinq uses lambda serialization and bytecode analysis. Let's start looking at Jinq with a Spring Boot example. Book Dependencies Add the following dependencies in the build.gradle file: implementation implementation 'org.springframework.boot:spring-boot-starter-data-jpa' 'org.jinq:jinq-jpa:1.8.32' Entity classes Consider the example with two tables in the database: and . Add the entity classes: books authors (name = ) { (strategy = GenerationType.IDENTITY) Long id; String title; published; Integer pages; (name = ) Author author; } @Entity "books" public class Book @Id @GeneratedValue private private private boolean private @ManyToOne @JoinColumn "author_id" private // getters and setters (name = ) { (strategy = GenerationType.IDENTITY) Long id; String firstName; String lastName; (mappedBy = , cascade = CascadeType.ALL, orphanRemoval = ) ( ) Set books = LinkedHashSet<>(); } @Entity "authors" public class Author @Id @GeneratedValue private private private @OneToMany "author" true @OrderBy "id" private final new // getters and setters Configuration and Helper We need to create a bean for using Jinq. JinqJPAStreamProvider { { JinqJPAStreamProvider(emf); } } @Configuration public class JinqProviderConfiguration @Bean JinqJPAStreamProvider jinqDataProvider (EntityManagerFactory emf) return new We need to use the method for creating streams. Let's add a helper class. JinqJPAStreamProvider#streamAll { EntityManager entityManager; JinqJPAStreamProvider jinqDataProvider; { .jinqDataProvider = jinqDataProvider; } { jinqDataProvider.streamAll(entityManager, clazz); } } @Component public class JinqHelper @PersistenceContext private private final public JinqHelper (JinqJPAStreamProvider jinqDataProvider) this public JPAJinqStream stream (Class clazz) return Now we are ready to query the database. Query Examples We can use the method to get the number of all authors. count authorsCount = jinqHelper.stream(Author.class).count(); long Let's retrieve all published books that have more than 50 pages. List books = jinqHelper.stream(Book.class).where(book -> book.getPages() > && book.isPublished()).toList(); 50 If we want to read-only specific columns, we can use the method and the or , ..., classes in the package. select Pair Tuple3 Tuple8 org.jinq.tuples List > allAuthors = jinqHelper.stream(Author.class) .where(author -> author.getFirstName().equals( )) .select(author -> Pair<>(author.getFirstName(), author.getLastName())) .toList(); (Pair author : allAuthors) { String firstName = author.getOne(); String lastName = author.getTwo(); } "Simon" new for // ... Jinq provides aggregation methods. Double avgPages = jinqHelper.stream(Book.class).avg(Book::getPages); We can use the method to perform join-queries. We also use the class in the following example joinList Pair List > joinedList = jinqHelper.stream(Author.class) .where(author -> author.getFirstName().equals( )) .joinList(Author::getBooks) .where(pair -> pair.getTwo().isPublished()) .toList(); "Simon" Advanced Features Jinq also provides support for grouping, sorting, different types of joins, subqueries, registering your own functions, and other useful features. Conclusion Jinq provides a convenient and natural way to build type-safe database queries. It is easier to use than JPA 1 Criteria API and does not require code generation as Query DSL or JPA 2 metamodel.