Issue with grid selection when storing objects

Question

Hi, 
 I'm trying this tutorial... 
 docs.appian.com/.../Grid_Tutorial.html 
 I'm interesting about the two code lines that enables to store the Object selected items : 
 selectionSaveInto { 
 a!save(local!selected Vehicles , append(local!selected Vehicles , fv!selectedRows)), a!save(local!selectedVehicles, difference(local!selected Vehicles , fv!deselectedRows)) 
 All works fine, but could you explain me why when I'm try to set local!selectedVehicles into a Rule Input. I obtain this error below please ?

I've just addied 2 lines of code : 
 a!localVariables ( 
 local!selected Vehicles : ri!selectedVehicles, /* that is the same type used for the grid data, CDT type with array values */ 
 ... 
 selectionSaveInto { 
 a!save(...), a!save(...), 
 a!save(ri !selectedVehicles, local!selectedVehicles)

Praful Singhal · Answer

problem occurs because of typecasting. you can typecast a map to cdt using typecast function and then saved it will not result in error. 
 or it can be avoided simply by doing this way also. 
 a!save(ri!selectedVehicles, difference(ri!selectedVehicles , fv!deselectedRows))

Praful Singhal · Answer

rule input is of type CDT CJT2_Vehicles when you assign it to local!selectedVehicles then the local!selectedVehicles also become of same type and while fv!deselectedRows is not of type CDT CJT2_Vehicles, type for fv!deselectedRows is a map(String, Object). so thats why you are facing this issue. You don`t need to cast local!selectedVehicles you just need to cast fv!deselectedRows to CDT type i.e 
 
 a!save( local!selectedVehicles, difference( local!selectedVehicles, { a!flatten( a!foreach( items: fv!deselectedRows, expression: cast( 'type!{urn:com:appian:types:cjt2}CJT2_Vehicles', fv!item ) ) ) } ) ) 
 or second option convert CDT to map using but i am not sure the line of code which i right below will change the cdt to map. But i think its worth to try 
 a!save(local!selectedVehicles,difference({local!selectedVehicles},{fv!deselectedRows}))