How to insert Foreign Key values from Form Input? - yesod

Question

Say I have the following relations :
Section
name Text
UniqueSection name
Subject
name Text
UniqueSubject name
Faculty
name Text
UniqueFaculty name
Assignment
section SectionId
faculty FacultyId
subject SubjectId
UniqueAssignment section subject
Handler:
postNewAssignmentR :: Handler Html
postNewAssignmentR = do
-- don't know what to use instead xxxField for SectionId/FacultyId/SubjectId
sec <- runInputPost $ ireq xxxField "section"
fac <- runInputPost $ ireq xxxField "faculty"
sub <- runInputPost $ ireq xxxField "subject"
runDB $ insert $ Assignment sec fac sub
setMessage "Created new Assignment"
redirect AssignmentsR
If "section", "faculty", and "subject" are dropdowns inputs with their corresponding Ids as values(in Text we get from runInputPost), how to convert them to sectionId, facultyId,..etc ?
or should I go for any other approach to insert foreign keys ?

Answer 1

I just realized you are not generating the forms using Yesod so my original suggestion below may not work. You can probably get the input value as an Int and then use fKey = Key $ PersistInt64 intReturnValue
Unsure if the code below will work for your case:
You can use selectField to get a list of Section Names and then populate it in your dropdown -- the values should map to IDs automatically. I don't use Input Forms but guessing something like this should work:
<*> ireq (selectField sections) "Section Name"
where
sections = do
entities <- runDB $ selectList [] [Asc SectionName]
optionsPairs $ map (\e -> (sectionName $ entityVal e, entityKey e)) entities