Using a CASE statement in HQL select - nhibernate

Question

Is there any way to do the following in HQL:
SELECT
case when flag = true then SUM(col1) else SUM(col2)
FROM
myTable

Answer 1

I guess you can (3.6, 4.3) [inline edit] ...for where-clauses:
"Simple" case, case ... when ... then ... else ... end, and "searched" case, case when ... then ... else ... end

Answer 2

Apparently the ability to do this was added in 3.0.4, with the limitation that you cannot use sub-selects in the else clause.

Answer 3

See Hibernate-Forum: https://forum.hibernate.org/viewtopic.php?t=942197
Answer from Team (Gavin):
case is supported in the where clause, but not in the select clause in HB3.
And seen in JIRA with State "Unresolved".

Answer 4

Below you can find a working query (hibernate on postgresql) that uses 2 case statements to replace a boolean value with the corresponding textual representation.
SELECT
CASE ps.open WHEN true THEN 'OPEN'
else 'CLOSED' END,
CASE ps.full WHEN true THEN 'FULL'
else 'FREE' END,
ps.availableCapacity
FROM ParkingState as ps

Answer 5

I facing the same problem in HQL then I solved the following query is
select CONCAT(event.address1,', ', CASE WHEN event.address2 IS NULL THEN '' ELSE concat(event.address2,', ') END, event.city from EventDetail event where event.startDate>=:startDate and event.endDate<=:endDate;

Answer 6

We use hibernate HQL query extensively and I think finally there is a hackish way of doing such a thing :
Assuming we originally had a query of
i2.element.id = :someId
Then decided to expand this to be something like this:
((i.element.id = :someId and i2.element.id=:someId) or (i2.element.id = :someId))
But there was an issue where we want it to only lookup for this based on classType so a case statement:
(case when type(i)=Item then
((i.element.id = :someId and i2.element.id=:someId) or (i2.element.id = :someId))
else
i.element.id = :someId
end)
Above will not work you could make an easy version of above work by doing:
(case when type(i)=Item then
i2.element.id
else
i.element.id
end)=:elementId
But this does not actually do what we need it to do, we want it to do exact above query, so knowing you can assign a variable at the end of a case statement in there where bit of HQL:
(
(
(case when
type(r)=Item then
i.element.id
else
i.element.id end) = :elementId
and
(case when
type(r)=Item then
i2.element.id
else
i.element.id end) = :elementId
)
or
(case when
type(r)=Item then
i2.element.id
else
i.element.id end) = :elementId
)
I have managed to make the query now work based on case statement, sure it is a lot more long winded but actually does the same as the first instance

Answer 7

This is an example using a string comparison in the condition:
SELECT CASE f.type WHEN 'REMOVE'
THEN f.previousLocation
ELSE f.currentLocation
END
FROM FileOperation f