fix: always drop constraints before modifying

fix: properly compare old references and new references

lib/migration_generator/migration_generator.ex

@@ -1122,8 +1122,8 @@ defmodule AshPostgres.MigrationGenerator do
         else
           [
             %Operation.AlterAttribute{
-              new_attribute: new_attribute,
-              old_attribute: old_attribute,
+              new_attribute: Map.delete(new_attribute, :references),
+              old_attribute: Map.delete(old_attribute, :references),
               table: snapshot.table
             }
           ]
@@ -1414,14 +1414,17 @@ defmodule AshPostgres.MigrationGenerator do
   end
 
   defp configured_reference(resource, attribute, relationship) do
-    resource
-    |> AshPostgres.references()
-    |> Enum.find(&(&1.relationship == relationship))
-    |> Kernel.||(%{
-      on_delete: nil,
-      on_update: nil,
-      name: "#{AshPostgres.table(resource)}_#{attribute}_fkey"
-    })
+    ref =
+      resource
+      |> AshPostgres.references()
+      |> Enum.find(&(&1.relationship == relationship))
+      |> Kernel.||(%{
+        on_delete: nil,
+        on_update: nil,
+        name: nil
+      })
+
+    Map.put(ref, :name, ref.name || "#{AshPostgres.table(resource)}_#{attribute}_fkey")
   end
 
   defp migration_type({:array, type}), do: {:array, migration_type(type)}
@@ -1560,7 +1563,9 @@ defmodule AshPostgres.MigrationGenerator do
         |> Map.update!(:destination_field, &String.to_atom/1)
         |> Map.put_new(:on_delete, nil)
         |> Map.put_new(:on_update, nil)
-        |> Map.put_new(:name, "#{table}_#{attribute.name}")
+        |> Map.update!(:on_delete, &(&1 && String.to_atom(&1)))
+        |> Map.update!(:on_update, &(&1 && String.to_atom(&1)))
+        |> Map.put(:name, Map.get(references, :name) || "#{table}_#{attribute.name}")
         |> Map.put_new(:multitenancy, %{
           attribute: nil,
           strategy: nil,

lib/migration_generator/operation.ex

@@ -357,17 +357,21 @@ defmodule AshPostgres.MigrationGenerator.Operation do
     # We only need to drop it before altering an attribute with `references/3`
     defstruct [:attribute, :table, :multitenancy, :direction, no_phase: true]
 
-    def up(%{table: table, references: reference, direction: :up}) do
+    def up(%{table: table, attribute: %{references: reference}, direction: :up}) do
       "drop constraint(:#{table}, #{inspect(reference.name)})"
     end
 
-    def up(_), do: ""
+    def up(_) do
+      ""
+    end
 
-    def down(%{table: table, references: reference, direction: :down}) do
+    def down(%{table: table, attribute: %{references: reference}, direction: :down}) do
       "drop constraint(:#{table}, #{inspect(reference.name)})"
     end
 
-    def down(_), do: ""
+    def down(_) do
+      ""
+    end
   end
 
   defmodule RenameAttribute do