GROUP_CONCAT does NOT work in QueryDSL

Hi there,

I am struggling to figure out how to use ‘GROUP_CONCAT’ in QueryDSL.

final QDataSourceSmallEliminate eliminate = QDataSourceSmallEliminate.dataSourceSmallEliminate;
		final QLattitudeVisitor lattitude = LattitudeVisitorServiceImpl.$;
//		Expressions.stringOperation(SQLOps.GROUP_CONCAT, lattitude.tagName)
		
		return QuerydslUtils.newQuery(entityManager).select(Projections.constructor(EliminateLattitude.class, 
				eliminate.id, 
				JPAExpressions.selectDistinct( SQLExpressions.groupConcat(lattitude.tagName)).from(lattitude).where(lattitude.urlCrc.eq(eliminate.urlCrc))))
			.from(eliminate)
			.fetch();

Exception:

org.springframework.dao.InvalidDataAccessApiUsageException: No pattern found for GROUP_CONCAT; nested exception is java.lang.IllegalArgumentException: No pattern found for GROUP_CONCAT

...

Caused by: java.lang.IllegalArgumentException: No pattern found for GROUP_CONCAT
	at com.querydsl.core.support.SerializerBase.visitOperation(SerializerBase.java:280)
	at com.querydsl.jpa.JPQLSerializer.visitOperation(JPQLSerializer.java:437)
	at com.querydsl.core.support.SerializerBase.visit(SerializerBase.java:231)
	at com.querydsl.core.support.SerializerBase.visit(SerializerBase.java:31)
	at com.querydsl.core.types.OperationImpl.accept(OperationImpl.java:83)
	at com.querydsl.core.support.SerializerBase.handle(SerializerBase.java:92)
	at com.querydsl.jpa.JPQLSerializer.serialize(JPQLSerializer.java:203)
	at com.querydsl.jpa.JPQLSerializer.visit(JPQLSerializer.java:358)
	at com.querydsl.jpa.JPQLSerializer.visit(JPQLSerializer.java:39)
	at com.querydsl.core.types.SubQueryExpressionImpl.accept(SubQueryExpressionImpl.java:57)
	at com.querydsl.core.support.FetchableSubQueryBase.accept(FetchableSubQueryBase.java:150)
	at com.querydsl.core.support.SerializerBase.handle(SerializerBase.java:92)
	at com.querydsl.core.support.SerializerBase.handle(SerializerBase.java:119)
	at com.querydsl.core.support.SerializerBase.visit(SerializerBase.java:225)
	at com.querydsl.core.support.SerializerBase.visit(SerializerBase.java:31)
	at com.querydsl.core.types.ConstructorExpression.accept(ConstructorExpression.java:112)
	at com.querydsl.core.support.SerializerBase.handle(SerializerBase.java:92)
	at com.querydsl.jpa.JPQLSerializer.serialize(JPQLSerializer.java:203)
	at com.querydsl.jpa.JPAQueryBase.serialize(JPAQueryBase.java:60)
	at com.querydsl.jpa.JPAQueryBase.serialize(JPAQueryBase.java:50)
	at com.querydsl.jpa.impl.AbstractJPAQuery.createQuery(AbstractJPAQuery.java:98)
	at com.querydsl.jpa.impl.AbstractJPAQuery.createQuery(AbstractJPAQuery.java:94)
	at com.querydsl.jpa.impl.AbstractJPAQuery.fetch(AbstractJPAQuery.java:201)
	at com.moraydata.general.secondary.repository.impl.DataSourceSmallEliminateRepositoryImpl.findObject(DataSourceSmallEliminateRepositoryImpl.java:98)
	at com.moraydata.general.secondary.repository.impl.DataSourceSmallEliminateRepositoryImpl$$FastClassBySpringCGLIB$$b42d875d.invoke(<generated>)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)

QueryDSL 4.2.1 & JDK1.8 & Spring Boot2.0 & MySQL 5.7.

I read through the latest reference doc still cannot find the answer, so what should I do to make it work ?

Please help. Thanks in advance. @Shredder121

[giraffe-tree]

@beamofsoul

if you use spring boot data jpa and querydsl-jpa , You can follow these steps

1. create a custom DB dialect and register function

//  org.hibernate.dialect.MySQL5Dialect
public class CustomMysqlDialect extends MySQL5Dialect {
    public CustomMysqlDialect() {
        super();
        // register custom/inner function here
        this.registerFunction("group_concat", new SQLFunctionTemplate(StandardBasicTypes.STRING, "group_concat(?1)"));
    }
}

1. config JpaVendorAdapter

@Configuration
public class JpaConfiguration {
    @Bean
    public JpaVendorAdapter jpaVendorAdapter() {
        AbstractJpaVendorAdapter adapter = new HibernateJpaVendorAdapter();
        adapter.setShowSql(true);
        adapter.setDatabase(Database.MYSQL);
       // package to CustomMysqlDialect
        adapter.setDatabasePlatform("com.xxx.xxx.config.CustomMysqlDialect");
        adapter.setGenerateDdl(false);
        return adapter;
    }
}

1. use query-dsl

// before do this , autowird JPAQueryFactory at first 
        QReportDoctorTag qReportDoctorTag = QReportDoctorTag.reportDoctorTag;
        SimpleTemplate<String> simpleTemplate = Expressions.simpleTemplate(String.class, "group_concat({0})", qReportDoctorTag.tag);
        JPAQuery<Tuple> tupleJPAQuery = queryFactory.select(qReportDoctorTag.reportId, simpleTemplate)
                .from(qReportDoctorTag)
                .groupBy(qReportDoctorTag.reportId);

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

[jwgmeligmeyling]

In JPA this is unsupported. You’ll have to ask your ORM vendor to implement it first (for example Hibernate).

You could consider using the blaze-persistence-querydsl extension to fill the gap: https://persistence.blazebit.com/documentation/1.5/core/manual/en_US/index.html#querydsl-integration

Which has the following methods:

• JPQLNextExpressions.groupConcat(Expression<?> expression, String separator, OrderSpecifier<?>... orderSpecifiers)
• JPQLNextExpressions.groupConcat(Expression<?> expression, Expression<String> separator, OrderSpecifier<?>... orderSpecifiers)
• JPQLNextExpressions.groupConcat(boolean distinct, Expression<?> expression, String separator, OrderSpecifier<?>... orderSpecifiers)
• JPQLNextExpressions.groupConcat(boolean distinct, Expression<?> expression, Expression<String> separator, OrderSpecifier<?>... orderSpecifiers)