Querydsl fin jug - june 2012


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Querydsl presentation at FinJUG in June 2012

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  • Hey Timo, thanks for your precious information/slide. It helped me a lot understanding Querydsl more than there official reference document. It covers everything what we need to know. But I am confused here. Can you give me any scenario where custom query classes and expressions can be useful. I have thought a lot. Please help me.
    Thanks again..
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Querydsl fin jug - june 2012

  1. 1. QuerydslType-safe queries for Java Timo Westkämper @timowest www.querydsl.com
  2. 2. 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
  3. 3. 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();
  4. 4. Before Querydsl● 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
  5. 5. 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
  6. 6. Querydsl● Domain model specific 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, JDO, SQL, Lucene, Mongodb... ● Once you know basics of one language, you know basics of all SQL-like Querydsl languages
  7. 7. Querydsl● Autocomplete with Java IDEs ● No need to remember exact syntax ● No need to remember property names● Better support for domain model refactoring ● When domain changes, queries show compile errors ● Autocomplete helps fixing those● Developed for real-life projects, e.g. Balancion and Cyclos● Business friendly license (Apache 2.0)
  8. 8. Querydsl● Development started in 2007 with public releases since 2008● Querydsl statistics: ● Approximately 24 000 LOC ● Test Code coverage about 75% (target 80%) ● Sonar reports ● FindBugs with extra annotations (@Nullable)● Discussions about standardisations● JDO/DataNucleus started with Querydsl...
  9. 9. Querydsl usage● Create your variables QPerson.person // default variable new QPerson("myPerson") // custom variable● Create your query JPAQuery, HibernateQuery, SQLQueryImpl etc● Populate your query from, where, groupBy, having, orderBy● Get the results count, iterate, list, uniqueResult
  10. 10. Querydsl usage● All expressions can be reused, immutables with caching – except BooleanBuilder and a few others● Queries, sub queries and BooleanBuilder are stateful builder with cascading methods
  11. 11. Overview of JPAQuery signaturefrom Query sourcesinnerJoin, join, leftJoin, fullJoin, on Join elements join(source, alias) [.on(source.prop.eq(alias.prop))]where Query filters, varargs for intersection (and) and(), or(), allOf(), anyOf()
  12. 12. Overview of JPAQuery signaturegroupBy Group by arguments in varargs formhaving Having filter of the "group by” as an varags array of Predicate expressions.orderBy Ordering of the result as an varargs array of order expressions. asc() and desc() on numeric, string and other comparable expressionlimit, offset, restrict Paging of the result Limit for max results and Offset for skipping rows and Restrict for defining both in one call
  13. 13. Overview of JPAQuery signaturelist Get the results as a typed ListlistResults Get the results as a typed List and total row count for pagingiterate Get the results as a typed Iteratorcount Get the row count as a longuniqueResult Get a typed single row result
  14. 14. Simple exampleQPerson 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);=>select person from com.acme.Person personwhere person.firstName eq = ?1 and person.lastName = ?2
  15. 15. Order// Get persons ordered by last name and first name (desc)query.from(person) .orderBy(person.lastName.asc(), person.firstName.desc()) .list(person);=>select person from Person personorder by person.lastname asc, person.firstName desc
  16. 16. Order// Get persons ordered by women firstquery.from(person) .orderBy(person.gender .when(Gender.FEMALE).then(0) .otherwise(1).asc()) .list(person);=>select person from Person personorder by case person.gender = Gender.FEMALE then 0 else 1 end asc
  17. 17. Grouping// Get person counts grouped by last namequery.from(person) .groupBy(person.lastName) .list(person.lastName, person.count());=>select person.lastName, count(person) from Person persongroup by person.lastName
  18. 18. Subqueries//Get persons with max child countQPerson parent = new QPerson("parent");query.from(person) .where(person.children.size().eq( new JPASubQuery().from(parent) .uniqueResult(parent.children.size().max()) )).list(person);=>select person from Person personwhere person.children.size() = ( select max(parent.children.size()) from Person parent)
  19. 19. Constructor projection// DTO class with @QueryProjection constructor annotationpublic class PersonInfo { long id; String name; @QueryProjection public PersonInfo(long id, String name) { this.id = id; this.name = name; }}// List PersonInfo DTOsList<PersonInfo> infos = query.from(person) .list(new QPersonInfo(person.id, person.lastName.concat(", ”).concat(person.firstName)));
  20. 20. Tuple projection// List ages of personsList<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");}
  21. 21. 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);
  22. 22. Update// Set firstName of all Does to Johnlong updatedRowCount =new JPAUpdateClause(getEntityManager(), person) .set(person.firstName, "John") .where(person.lastName.eq("Doe")) .execute();=>update Person personset person.firstName = ?1where person.lastName = ?2
  23. 23. Delete// Delete all John Doeslong updatedRowCount =new JPADeleteClause(getEntityManager(), person) .where(person.lastName.eq("Doe"), person.firstName.eq("John")) .execute();=>delete Person personwhere person.lastName = ?1 and person.firstName = ?2
  24. 24. 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
  25. 25. 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)
  26. 26. Delegate methodspublic class MyQueryExtensions { @QueryDelegate(Date.class) public static NumberExpression<Integer> yearAndMonth(DateTimePath<Date> date) { return date.year().multiply(100).add(date.month()); }}=>package ext.java.util;...public class QDate extends DateTimePath<java.util.Date> {... public NumberExpression<Integer> yearAndMonth() { return MyQueryExtensions.yearAndMonth(this); }}
  27. 27. Template expressions// ilikequery.from(person).where(BooleanTemplate.create("{0} ilike {1}”, person.lastName, ConstantImpl.create("P%"))).list(person);=>select person from Person personwhere person.lastName ilike ?1
  28. 28. Custom query classespublic 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))); }}
  29. 29. 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
  30. 30. Criteria example// All possible pairs of single males and femalesCriteriaQuery<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 ) );
  31. 31. Querydsl example// All possible pairs of single males and femalesJPAQuery 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));
  32. 32. SQL● Pretty similar to JPA/Hibernate ● No deep paths over relations though ● No implicit joins SQLTemplates templates = new MySQLTemplates(); ... SQLQuery query = new SQLQueryImpl(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);
  33. 33. 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
  34. 34. 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 ");
  35. 35. JPA/Hibernate Maven Integration<build><plugins><plugin> <groupId>com.mysema.maven</groupId> <artifactId>maven-apt-plugin</artifactId> <version>1.0.3</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>
  36. 36. 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>
  37. 37. What does Mysema offer for Querydsl?● Free public support ● GitHub Issues ● Querydsl Google Group ● Mysema Blog● Consulting services ● User support ● Custom extensions and integration ● Training
  38. 38. Querydsl support from other companies● VMware uses Querydsl in Spring Data for the following backends ● JPA ● SQL/JDBC ● MongoDB ● Neo4j● Spring Data is a good option if you want to use repositories in Spring with Querydsl support
  39. 39. Questions?
  40. 40. Thanks!Timo Westkämper @timowestwww.querydsl.comwww.mysema.com