I have a list of columns as List<String> columns, and I would like to retrieve those columns using queryDSL.
I have this working -
queryFactory = new JPAQueryFactory(entityManager); //where entityManager is a JPA EntityManager
JPAQuery<?> query = queryFactory.query();
QEmployee employee= QEmployee.employee;
List<Tuple> result = query.select(employee.firstName, employee.lastNameemployee.lastName ,employee.age)
.from(employee)
.fetch();
This works fine in my test. But here I am specifying the column explicitly in the select(..) part. If my List has only firstName and age like
List<String> columnList = Arrays.asList("firstName" , "age");
then I only want to retrieve those two column from my select(..) part. QueryDSL select part only accepts Expressions, so I tried doing this:
StringExpression[] columnListExpression = columnList.toArray(new StringExpression[columnList.size()])
and then passed columnListExpression to my select(..) part as shown below,
List<Tuple> result = query.select(columnListExpression) // doesn't work
.from(employee)
.fetch();
however I get a Unsupported Operation Exception. I wanted to use queryDSL because that way I can easily construct the Predicate at runtime in a type safe manner. This SO question brushes the topic, but it was 5 years ago and now we have QueryDSL 5.0 How do I select only those columns that are present my List using queryDSL?
Something like this worked:
PathBuilder<Employee> entityPath = new PathBuilder<>( Employee .class, "entity");
List<com.querydsl.core.Tuple> employeeResults = query.select(
entityPath.get(" firstName ", String.class)
,entityPath.get("age", Integer.class))
.from(entityPath)
.fetch();
However, I don't know the columns before hand and need to construct this select(..) part dynamically.
