Conditional concatenation in DB-mapping

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1

In the DB-mapping I would like to concatenate a text value with a specific fixed text, depending on the value of another text field. Something like this (pseudo-code!):

'Relatienummer': text = match $ .'Relatiesoort' equals "D"
	| true = concat ( "16" , to-text $ .'Relatienummer' )
	| false = match $ .'Relatiesoort' equals "C"
		| true = concat ( "25" , to-text $ .'Relatienummer' )
		| false = to-text $ .'Relatienummer'

But it seems that match doesn’t work with type text. How to handle this?

2

The probleem here is that match is part of the state mapping, so it can only be used to assign a stategroup.
With the exception of switch on enum, the RDB only supports conditional expressions when assigning a stategroup.

3

Where and how should I then concatenate the required text to the DB-text field, depending on the other DB-text field?

4

The match must be a part of the expression setting the stategroup, but multiple branches in the state mapping can result in the same state:

'State Group': stategroup = match ...
  | true = 'State' (
    'Value': text = concat ( "16", ... )
  )
  | false = 'State' (
    'Value': text = concat ( "25", ... )
 )
5

Alternatively 'Relatiesort' can be changed from a text to an enum in the table definition (database.alan). This requires that 'Relatiesort' has a predefined set of possible values.
This allows you to switch on the enum in a text expression.

'Value': text = switch $ ?'Enum DB Field' (
  |'Enum Value A' = concat ( "16", ... )
  |'Enum Value B' = concat ( "25", ... )
  ...
)