Package com.blazebit.persistence.querydsl

The 
blaze-persistence-integration-querydsl-expressions
module implements an extended expression model for Blaze-Persistence JPQL.Next.

The module provides a BlazeJPAQuery as a default implementation of JPQLNextQuery, which extends the all familiar JPQLQuery. BlazeJPAQuery is analog to JPAQuery. Users can implement extensions on top of JPQLNextQuery by extending AbstractBlazeJPAQuery.

BlazeJPAQuery can be serialized using the JPQLNextSerializer, and may be rendered to a CriteriaBuilder using the BlazeCriteriaBuilderRenderer. This allows for the queries to be executed through Blaze-Persistence JPQL.Next query engine. Be sure to use the JPQLNextTemplates or any Templates implementation that includes the extensions from JPQLNextTemplates when using JPQL.Next specific features (e.g. window functions, values clauses, set operations, common table expressions).

This module aims an API that is as close to the original QueryDSL API as possible. Where features did not exist in 

querydsl-jpa
, but did exist in 
querydsl-sql
, we stayed as close to the existing SQL implementation as possible. This includes the implementation for window functions, common table expressions (CTEs) and union queries which was the basis for all types of set expressions.

Staying close to QueryDSL's API however, also means that the API is not as fluent as Blaze-Persistence users are accustomed to. This means that creating common table expressions or complex set operations may lead to superfluous code.

Examples

The following chapters demonstrate some of the possibilities of the 
blaze-persistence-integration-querydsl-expressions
integration.

Plain query

 QTestEntity testEntity = QTestEntity.testEntity;

 BlazeJPAQuery<Tuple> query = new BlazeJPAQuery<Tuple>(entityManager, cbf).from(testEntity)
         .select(testEntity.field.as("blep"), testEntity.field.substring(2))
         .where(testEntity.field.length().gt(1));

 List<Tuple> fetch = query.fetch();

Implicit joins

Contrary to JPQL, JPQL.Next allows for implicit joins. For deep path expressions it is not necessary to specify the joins manually. 

 List<Book> dilbert = new BlazeJPAQuery<>(entityManager, cbf).from(book)
                     .where(book.author.name.eq("Dilbert"))
                     .select(book).fetch();

Window functions

 QTestEntity sub = new QTestEntity("sub");
 BlazeJPAQuery<Tuple> query = new BlazeJPAQuery<Tuple>(entityManager, cbf).from(testEntity)
         .select(testEntity.field.as("blep"), JPQLNextExpressions.rowNumber(), JPQLNextExpressions.lastValue(testEntity.field).over().partitionBy(testEntity.id))
         .where(testEntity.id.in(select(sub.id).from(sub)));

 List<Tuple> fetch = query.fetch();

Named window functions

 QTestEntity sub = new QTestEntity("sub");
 NamedWindow blep = new NamedWindow("whihi").partitionBy(testEntity.id);

 BlazeJPAQuery<Tuple> query = new BlazeJPAQuery<Tuple>(entityManager, cbf).from(testEntity)
         .window(blep)
         .select(testEntity.field.as("blep"), JPQLNextExpressions.rowNumber().over(blep), JPQLNextExpressions.lastValue(testEntity.field).over(blep))
         .where(testEntity.id.in(select(sub.id).from(sub)));

 List<Tuple> fetch = query.fetch();

Regular association joins

 Map<Author, List<Book>> booksByAuthor = new BlazeJPAQuery<>(entityManager, cbf)
         .from(author)
         .innerJoin(author.books, book)
         .transform(GroupBy.groupBy(author).as(GroupBy.list(book)));

Regular entity joins

 QAuthor otherAuthor = new QAuthor("otherAuthor");
 QBook otherBook = new QBook("otherBook");
 Map<Author, List<Book>> booksByAuthor = new BlazeJPAQuery<Tuple>(entityManager, cbf)
         .from(otherAuthor)
         .innerJoin(otherBook).on(otherBook.author.eq(otherAuthor))
         .transform(GroupBy.groupBy(otherAuthor).as(GroupBy.list(otherBook)));

Managed type values clause

 Book theBook = new Book();
 theBook.id = 1337L;
 theBook.name = "test";

 List<Book> fetch = new BlazeJPAQuery<Book>(entityManager, cbf)
         .fromValues(book, Collections.singleton(theBook))
         .select(book)
         .fetch();

Managed attribute values clause

 StringPath bookName = Expressions.stringPath("bookName");

 List<String> fetch = new BlazeJPAQuery<>(entityManager, cbf)
         .fromValues(book.name, bookName, Collections.singleton("book"))
         .select(bookName)
         .fetch();

Common Table Expressions

First declare your CTE entity:

 @CTE
 @Entity
 public class IdHolderCte {

     @Id
     Long id;

     String name;

 }

Next, it can be queried as such:

 List<Long> fetch = new BlazeJPAQuery<TestEntity>(entityManager, cbf)
     .with(idHolderCte, select(
             JPQLNextExpressions.bind(idHolderCte.id, book.id),
             JPQLNextExpressions.bind(idHolderCte.name, book.name)).from(book))
     .select(idHolderCte.id).from(idHolderCte)
     .fetch();

Note: Set operations are also allowed in CTEs, and through set operations it is also possible to write recursive CTEs.

Subquery joins

A limitation of JPQL frequently stumbled opon, is that subqueries cannot be joined. With Blaze-Persistence however, this is perfectly possible:

 QRecursiveEntity recursiveEntity = new QRecursiveEntity("t");

 List<RecursiveEntity> fetch = new BlazeJPAQuery<>(entityManager, cbf)
         .select(recursiveEntity)
         .from(JPAExpressions.select(recursiveEntity)
                 .from(recursiveEntity)
                 .where(recursiveEntity.parent.name.eq("root1"))
                 .orderBy(recursiveEntity.name.asc())
                 .limit(1L), recursiveEntity)
         .fetch();

The subquery may project any managed entity, including CTEs.

Lateral joins

Subquery joins are allowed to access outer query variables, if a lateral join is used.

 QRecursiveEntity t = new QRecursiveEntity("t");
 QRecursiveEntity subT = new QRecursiveEntity("subT");
 QRecursiveEntity subT2 = new QRecursiveEntity("subT2");

 List<Tuple> fetch = new BlazeJPAQuery<>(entityManager, cbf)
         .select(t, subT2)
         .from(t)
         .leftJoin(JPAExpressions.select(subT).from(t.children, subT).orderBy(subT.id.asc()).limit(1), subT2)
         .lateral()
         .fetch();
Author:
Jan-Willem Gmelig Meyling