Validation expressions and dynamic `SET_PICKLIST`/`RESTRICT_PICKLIST`

[bryanburgers]

I am interested in using RCP WEBAPI-019 to run client-side validations on a listing input project.

I'm reading through RCP - WEBAPI-019 Validation Exrpession in the WebAPI on Confluence and Validation Expression Grammer in darnjo/rcp019 (linked from RESOStandards/transport's web-api-validation-expression.md),

I'm looking right now at dynamic picklists based on other values, and I don't quite see how it works.

Let's say as the simplest case, I have the following two fields, "ExampleCategory" and "ExampleSubcategory". A user chooses a value from "ExampleCategory" and that changes what is available to select in "ExampleSubcategory".

ExampleCategory	ExampleSubcategory
One	One A
One	One B
One	One C
Two	Two A
Two	Two B
Three	Three A
Three	Three B
Three	Three C

If the user chooses "Two" for ExampleCategory, I'd like the ExampleSubcategory options to be "Two A", "Two B".

It seems like the spec is close.

• There's a SET_PICKLIST action that would allow for setting which values of the picklist to display.
• There's a boolean expression [ExampleCategory] == "Two" for determining what the user has selected.
• There is an expression that can return a set or list of picklist items SET("Two A", "Two B") to return which picklist items to display.

But how can they be combined?

• As far as I can tell from the spec, there isn't any if/then or ternary operator that would allow returning the value

  [ExampleCategory] == "One" ? SET("One A", "One B", "One C") : ([ExampleCategory] == "Two" ? SET("Two A", "Two B") : ([ExampleCategory] == "Three" ? SET("Three A", "Three B", "Three C") : SET()))

• The above would get unwieldy quickly anyway; it would be nice to have them in separate actions somehow? But as far as I can tell from the spec, only SET actions get run after an ACCEPT?

  { "ruleSet": [
  { "field": "ExampleCategory", "action": "ACCEPT", "expression": "[ExampleCategory] == \"One\"" },
  { "field": "ExampleSubcategory", "action": "SET_PICKLIST", "expression": "SET(\"One A\", \"One B\", \"One C\")" },
  { "field": "ExampleCategory", "action": "ACCEPT", "expression": "[ExampleCategory] == \"Two\"" },
  { "field": "ExampleSubcategory", "action": "SET_PICKLIST", "expression": "SET(\"Two A\", \"Two B\")" },
  { "field": "ExampleCategory", "action": "ACCEPT", "expression": "[ExampleCategory] == \"Three\"" },
  { "field": "ExampleSubcategory", "action": "SET_PICKLIST", "expression": "SET(\"Three A\", \"Three B\", \"Three C\")" },
  ]}

• I don't think expressions that evaluate to false or a LIST are allowed in SET_PICKLIST

  { "ruleSet": [
  {
    "field": "ExampleSubcategory",
    "action": "SET_PICKLIST",
    "expression": "[ExampleCategory] == \"One\" .AND. SET(\"One A\", \"One B\", \"One C\")"
  },
  {
    "field": "ExampleSubcategory",
    "action": "SET_PICKLIST",
    "expression": "[ExampleCategory] == \"Two\" .AND. SET(\"Two A\", \"Two B\")"
  },
  {
    "field": "ExampleSubcategory",
    "action": "SET_PICKLIST",
    "expression": "[ExampleCategory] == \"Three\" .AND. SET(\"Three A\", \"Three B\", \"Three C\")"
  }
  ]}

• The Rules resource only has one RuleExpression field, so there's no option for something like a "test expression" and a "value expression"

  { "ruleSet": [
  {
    "field": "ExampleSubcategory",
    "action": "SET_PICKLIST",
    "testExpression": "[ExampleCategory] == \"One\"",
    "valueExpression": "SET(\"One A\", \"One B\", \"One C\")"
  },
  {
    "field": "ExampleSubcategory",
    "action": "SET_PICKLIST",
    "testExpression": "[ExampleCategory] == \"Two\"",
    "valueExpression": "SET(\"Two A\", \"Two B\")"
  },
  {
    "field": "ExampleSubcategory",
    "action": "SET_PICKLIST",
    "testExpression": "[ExampleCategory] == \"Three\"",
    "valueExpression": "SET(\"Three A\", \"Three B\", \"Three C\")"
  }
  ]}

I really love the idea of SET_PICKLIST/RESTRICT_PICKLIST if I can understand how to get it to work. What am I missing?