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Querydsl overview 2014

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Querydsl presentation

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Querydsl overview 2014

  1. 1. Querydsl Most popular querying tool for Java Timo Westkämper @timowest www.querydsl.com
  2. 2. What? ● Querydsl is an easy to use unified type-safe query language ● Compile time query validation ● Instant feedback on query errors ● Compact and intuitive fluent syntax ● Syntactically close to SQL ● Great for dynamic query building ● Supports multiple back-ends and query languages with consistent query API ● JPA/Hibernate, Mongodb, SQL, Lucene...
  3. 3. Why? ● Querydsl makes you more productive and your code less errorprone ● Query syntax validation by execution is slow and breaks the flow ● Each back-end has its own query language and API ● SQL-like for JPA and JDO, but not for MongoDB and Lucene ● Verbose parameter binding by name or position to parameter placeholders of a prepared statement ● Or risk injection attack if parameters are directly concatenated to query
  4. 4. How? QPerson person = QPerson.person; JPAQuery query = new JPAQuery(entityManager); List<Person> persons = query.from(person) .where( person.firstName.eq("John"), person.lastName.eq("Doe")) .list(person); is translated into select person from com.acme.Person person where person.firstName eq = ?1 and person.lastName = ?2
  5. 5. Before Querydsl ● Queries as strings within code TypedQuery<Person> query = em.createQuery( "select person from Person person " + "where person.firstName = ?1", Person.class); query.setParameter(1, "Max"); List<Person> persons = query.getResultList(); ● Must remember query syntax, domain classes, properties and relationships ● Syntax reference always at hand ● Domain model/schema reference at hand ● High cognitive overhead ● Error-prone
  6. 6. Before Querydsl ● Dynamic query building by string concatenation ● Very hard with multiple joins, ordering and complex conditionals depending on actual parameters StringBuilder where = new StringBuilder(); if (firstName != null) where.append("person.firstName = :firstName"); ... TypedQuery<Person> query = entityManager.createQuery( "select person from Person person where " + where, Person.class); if (firstName != null) query.setParameter("firstName", firstName); ... List<Person> persons = query.getResultList();
  7. 7. Before Querydsl ● Hibernate Criteria API as an alternative? ● Better for dynamic queries and has easier parameter binding, but... ● Lacking expressivity, unintuitive, verbose, cognitive overhead for schema if not for syntax, not type-safe, slow validation... ● Hibernate with three query languages to master with different focuses and expressivity
  8. 8. Querydsl to the rescue! ● Create your variables QPerson.person // default variable new QPerson("myPerson") // custom variable ● Create your query JPAQuery, HibernateQuery, SQLQuery etc ● Populate your query from, where, groupBy, having, orderBy ● Get the results count, iterate, list, uniqueResult
  9. 9. Order // Get persons ordered by last name and first name (desc) query.from(person) .orderBy(person.lastName.asc(), person.firstName.desc()) .list(person); translated into select person from Person person order by person.lastname asc, person.firstName desc
  10. 10. Order // Get persons ordered by women first query.from(person) .orderBy(person.gender .when(Gender.FEMALE).then(0) .otherwise(1).asc()) .list(person); translated into select person from Person person order by case person.gender = Gender.FEMALE then 0 else 1 end asc
  11. 11. Grouping // Get person counts grouped by last name query.from(person) .groupBy(person.lastName) .list(person.lastName, person.count()); translated into select person.lastName, count(person) from Person person group by person.lastName
  12. 12. Subqueries //Get persons with max child count QPerson parent = new QPerson("parent"); query.from(person) .where(person.children.size().eq( new JPASubQuery().from(parent) .uniqueResult(parent.children.size().max()) )).list(person); translated into select person from Person person where person.children.size() = ( select max(parent.children.size()) from Person parent)
  13. 13. Constructor projection // DTO class with @QueryProjection constructor annotation public class PersonInfo { long id; String name; @QueryProjection public PersonInfo(long id, String name) { this.id = id; this.name = name; } } // List PersonInfo DTOs List<PersonInfo> infos = query.from(person) .list(new QPersonInfo(person.id, person.lastName.concat(", ”).concat(person.firstName)));
  14. 14. Tuple projection // List ages of persons List<Tuple> tuples = query.from(person) .list(new QTuple( person.lastName, person.firstName, person.yearOfBirth)); for (Tuple tuple : tuples){ // Typed access to mapped query results! String name = tuple.get(person.firstName) + " " + tuple.get(person.lastName); int age = tuple.get(person.yearOfBirth) - getCurrentYear(); System.out.println(name + " is " + age + " years"); }
  15. 15. BooleanBuilder ● Helper for building complex Boolean expressions dynamically BooleanBuilder nameDisjunction = new BooleanBuilder(); for (String name : names) { nameDisjunction.or(person.firstName.like(name)); nameDisjunction.or(person.lastName.like(name)); } query.where(nameDisjunction);
  16. 16. Update // Set firstName of all Does to John long updatedRowCount = new JPAUpdateClause(getEntityManager(), person) .set(person.firstName, "John") .where(person.lastName.eq("Doe")) .execute(); translated into update Person person set person.firstName = ?1 where person.lastName = ?2
  17. 17. Delete // Delete all John Does long updatedRowCount = new JPADeleteClause(getEntityManager(), person) .where(person.lastName.eq("Doe"), person.firstName.eq("John")) .execute(); translated into delete Person person where person.lastName = ?1 and person.firstName = ?2
  18. 18. Querydsl extensions ● Customize the code generation ● @QueryType(PropertyType.NONE) ● Non searchable ● @QueryType(PropertyType.SIMPLE) ● Equality comparisons only (eq, ne, in) ● Custom query classes ● Extend abstract super classes and preserve fluent API ● Custom expressions ● Static delegate methods with @QueryDelegate ● Template expressions for e.g. custom SQL functions
  19. 19. Querydsl extensions ● Query serialization can be customized ● Works for JPA, JDO and SQL ● SQL dialects ● Overriding default templates (e.g. String#startsWith with like or regexp or...) ● Expression DSL can be replaced ● E.g. Querydsl for Scala ● Custom back-ends ● Lucene (10 classes) + Mongodb (6 classes)
  20. 20. Delegate methods public class MyQueryExtensions { @QueryDelegate(Date.class) public static NumberExpression<Integer> yearAndMonth(DateTimePath<Date> date) { return date.year().multiply(100).add(date.month()); } } causes code generation of package ext.java.util; ... public class QDate extends DateTimePath<java.util.Date> { ... public NumberExpression<Integer> yearAndMonth() { return MyQueryExtensions.yearAndMonth(this); } }
  21. 21. Template expressions // ilike query.from(person) .where(BooleanTemplate.create("{0} ilike {1}”, person.lastName, ConstantImpl.create("P%"))) .list(person); translated into select person from Person person where person.lastName ilike ?1
  22. 22. Custom query classes public class PersonQuery extends AbstractJPAQuery<PersonQuery> { final QPerson person = QPerson.person; public PersonQuery(EntityManager em) { super(em); from(person); } public PersonQuery nameMatches(String name) { return where(person.firstName.like(name) .or(person.lastName.like(name))); } }
  23. 23. JPA 2.0 Criteria vs Querydsl ● JPA 2 Criteria is the standard for type-safe queries in JPA, but Querydsl is in our opinion superior in many ways ● Easier and less verbose syntax ● Customizable ● Supports multiple back-ends – not just JPA ● JPA has a difficult to use static query-model ● Verbose property paths ● Operations via builder object ● Inverse order: “equals property value” vs. “property equals value” ● Broken flow
  24. 24. Criteria example // All possible pairs of single males and females CriteriaQuery<Person> query = builder.createQuery(Person.class); Root<Person> men = query.from( Person.class ); Root<Person> women = query.from( Person.class ); Predicate menRestriction = builder.and( builder.equal( men.get( Person_.gender ), Gender.MALE ), builder.equal( men.get( Person_.relationshipStatus ), RelationshipStatus.SINGLE ) ); Predicate womenRestriction = builder.and( builder.equal( women.get( Person_.gender ), Gender.FEMALE ), builder.equal( women.get( Person_.relationshipStatus ), RelationshipStatus.SINGLE ) ); query.where( builder.and( menRestriction, womenRestriction ) );
  25. 25. Querydsl example // All possible pairs of single males and females JPAQuery query = new JPAQuery(entityManager); QPerson men = new QPerson("men"); QPerson women = new QPerson("women"); query.from(men, women).where( men.gender.eq(Gender.MALE), men.relationshipStatus.eq(RelationshipStatus.SINGLE), women.gender.eq(Gender.FEMALE), women.relationshipStatus.eq(RelationshipStatus.SINGLE));
  26. 26. SQL ● Pretty similar to JPA/Hibernate ● No deep paths over relations though ● No implicit joins SQLTemplates templates = new MySQLTemplates(); ... SQLQuery query = new SQLQuery(connection, templates); query.from(person); query.innerJoin(parent).on(parent.id.eq(person.parent.id)); ● Shortcut for joins with foreign keys query.innerJoin(person.parentFK, parent);
  27. 27. SQL ● Maven plugin for generating query model ● Support for special SQL constructs and extensions ● Databases supported include ● MySQL ● PostgreSQL ● Oracle ● MS SQL Server ● H2 ● HSQLDB ● Derby ● SQLite ● CUBRID ● Teradata
  28. 28. SQL extensions ● Sub class of AbstractSQLQuery ● e.g. OracleQuery with connectByPrior ● Template expressions ● Direct addition of “flags” SQLInsertClause insert = new SQLInsertClause(connection, templates, person); insert.addFlag(Position.START_OVERRIDE, "replace into ");
  29. 29. Collections ● Provides querying functionality over collections of beans with joins, filtering and sorting ● The same metamodel types can be used like for e.g. JPA and Mongodb List<User> users = CollQueryFactory.from(user, users) .where(user.firstName.eq(“Bob”)) .list(user);
  30. 30. JPA/Hibernate Maven Integration <build><plugins><plugin> <groupId>com.mysema.maven</groupId> <artifactId>apt-maven-plugin</artifactId> <version>1.0.9</version> <executions> <execution> <goals><goal>process</goal></goals> <configuration> <outputDirectory>target/generated-sources/java</outputDirectory> <processor>com.mysema.query.apt.jpa.JPAAnnotationProcessor</processor> </configuration> </execution> </executions> </plugin></plugins></build>
  31. 31. SQL Maven Integration <build><plugins><plugin> <groupId>com.mysema.querydsl</groupId> <artifactId>querydsl-maven-plugin</artifactId> <version>${querydsl.version}</version> <executions><execution> <goals><goal>export</goal></goals> </execution></executions> <configuration> <jdbcDriver>org.apache.derby.jdbc.EmbeddedDriver</jdbcDriver> <jdbcUrl>jdbc:derby:target/demoDB;create=true</jdbcUrl> <!—- optional elements : namePrefix, jdbcUser, jdbcPassword, schemaPattern, tableNamePattern --> <packageName>com.myproject.domain</packageName> <targetFolder>${project.basedir}/target/generated-sources/java</targetFolder> </configuration> <dependencies><dependency> <!—- jdbc driver dependency --> <groupId>org.apache.derby</groupId> <artifactId>derby</artifactId> <version>${derby.version}</version> </dependency></dependencies> </plugin></plugins></build>
  32. 32. What services does Mysema offer for Querydsl? ● Free public support ● GitHub Issues ● Querydsl Google Group ● Mysema Blog ● Consulting services ● User support ● Custom extensions and integration ● Training
  33. 33. Questions?
  34. 34. Thanks! Timo Westkämper @timowest www.querydsl.com www.mysema.com

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