From b7394cab7c64218654143831d6d2c06f834af72c Mon Sep 17 00:00:00 2001
From: Amitai Burstein <amitai@gizra.com>
Date: Sat, 16 Sep 2023 20:54:33 +0300
Subject: [PATCH] Add type classes to allow use didChange

---
 IHP/View/Form.hs | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/IHP/View/Form.hs b/IHP/View/Form.hs
index 032db6b2f..67f5f39e9 100644
--- a/IHP/View/Form.hs
+++ b/IHP/View/Form.hs
@@ -19,7 +19,7 @@ import           IHP.ViewSupport
 import qualified Text.Blaze.Html5                   as Html5
 import IHP.HSX.ToHtml
 import GHC.Types
-import IHP.ModelSupport (getModelName, inputValue, isNew, Id', InputValue)
+import IHP.ModelSupport (didChange, getModelName, inputValue, isNew, Id', InputValue)
 import IHP.HSX.QQ (hsx)
 import IHP.View.Types
 import IHP.View.Classes ()
@@ -724,10 +724,12 @@ selectField :: forall fieldName model item.
     ( ?formContext :: FormContext model
     , HasField fieldName model (SelectValue item)
     , HasField "meta" model MetaBag
+    , Typeable model
     , KnownSymbol fieldName
     , KnownSymbol (GetModelName model)
     , CanSelect item
     , InputValue (SelectValue item)
+    , Eq (SelectValue item)
     ) => Proxy fieldName -> [item] -> FormField
 selectField field items = FormField
         { fieldType =
@@ -738,15 +740,7 @@ selectField field items = FormField
                  SelectInput (map itemToTuple items)
         , fieldName = cs fieldName
         , fieldLabel = removeIdSuffix $ fieldNameToFieldLabel (cs fieldName)
-        -- The select field is always displaying the value it gets from the nodel passed to the formFor.
-        -- The issue is introduced basically by the `newRecord @Record`. The `newRecord` call in the controller creates an empty record setting all fields to a default empty value.
-        --  The default empty value for UUIDs is the 00000000-0000-0000-0000-000000000000 and the default empty value for
-        -- enums is the first enum value.
-        -- Now, if we have a required field, we want to make sure the user selects a value, in the same
-        -- way they have to select for a reference field.
-        , fieldValue = if isNew model
-            then ""
-            else inputValue (getField @fieldName model :: SelectValue item)
+        , fieldValue = fieldValue
         , fieldInputId = cs (lcfirst (getModelName @model) <> "_" <> cs fieldName)
         , validatorResult = getValidationViolation field model
         , fieldClass = ""
@@ -765,6 +759,15 @@ selectField field items = FormField
     where
         fieldName = symbolVal field
         FormContext { model } = ?formContext
+        -- The select field is always displaying the value it gets from the nodel passed to the formFor.
+        -- The issue is introduced basically by the `newRecord @Record`. The `newRecord` call in the controller creates an empty record setting all fields to a default empty value.
+        --  The default empty value for UUIDs is the 00000000-0000-0000-0000-000000000000 and the default empty value for
+        -- enums is the first enum value.
+        -- Now, if we have a required field, we want to make sure the user selects a value, in the same
+        -- way they have to select for a reference field.
+        fieldValue = if isNew model && not (didChange field model)
+                    then ""
+                    else inputValue (getField @fieldName model :: SelectValue item)
 {-# INLINE selectField #-}
 
 -- | Radio require you to pass a list of possible values to select. We use the same mechanism as for for 'selectField'.