QGIS modelbuilder, having a choicebox/value map of strings as string input

I have kind of found my answer though it is kind of annoying and I wish there was a better one.

STEP ONE:

To get a choice box you have to use the FIELD MAPPER input parameter and then define your choices there. However keep in mind that these are actually numbers that need to be converted to strings.

STEP TWO:

The problem is however when you convert a number to a string, you of course do not have the actual value of the mapper. To make sure it gets the right value you build a CASE EXPRESION in the column where the value is to be inputed.

CASE 
WHEN to_string(@achtergrondondergrond2) ='0'
THEN
'GRB'
WHEN to_string(@achtergrondondergrond2) ='1'
THEN
'CADMAP'
WHEN to_string(@achtergrondondergrond2) ='2'
THEN
'KADVEC'
WHEN to_string(@achtergrondondergrond2) ='3'
THEN
'KADSCAN'
WHEN to_string(@achtergrondondergrond2) ='4'
THEN
'WPB'
WHEN to_string(@achtergrondondergrond2) ='5'
THEN
'TOPO'
WHEN to_string(@achtergrondondergrond2) ='6'
THEN
'ANDERE'
ELSE
null 
End

And your done, wish there was a better solution but this is the best we can do now apparently.