feat: member user relation

lib/membership/member.ex

@@ -13,7 +13,11 @@ defmodule Mv.Membership.Member do
 
     create :create_member do
       primary? true
+      # Properties can be created along with member
       argument :properties, {:array, :map}
+      # Allow user to be passed as argument for relationship management
+      # user_id is NOT in accept list to prevent direct foreign key manipulation
+      argument :user, :map, allow_nil?: true
 
       accept [
         :first_name,
@@ -32,12 +36,29 @@ defmodule Mv.Membership.Member do
       ]
 
       change manage_relationship(:properties, type: :create)
+
+      # Manage the user relationship during member creation
+      change manage_relationship(:user, :user,
+               # Look up existing user and relate to it
+               on_lookup: :relate,
+               # Error if user doesn't exist in database
+               on_no_match: :error,
+               # Error if user is already linked to another member (prevents "stealing")
+               on_match: :error,
+               # If no user provided, that's fine (optional relationship)
+               on_missing: :ignore
+             )
     end
 
     update :update_member do
       primary? true
+      # Required because custom validation function cannot be done atomically
       require_atomic? false
+      # Properties can be updated or created along with member
       argument :properties, {:array, :map}
+      # Allow user to be passed as argument for relationship management
+      # user_id is NOT in accept list to prevent direct foreign key manipulation
+      argument :user, :map, allow_nil?: true
 
       accept [
         :first_name,
@@ -56,6 +77,18 @@ defmodule Mv.Membership.Member do
       ]
 
       change manage_relationship(:properties, on_match: :update, on_no_match: :create)
+
+      # Manage the user relationship during member update
+      change manage_relationship(:user, :user,
+               # Look up existing user and relate to it
+               on_lookup: :relate,
+               # Error if user doesn't exist in database
+               on_no_match: :error,
+               # Error if user is already linked to another member (prevents "stealing")
+               on_match: :error,
+               # If no user provided, remove existing relationship (allows user removal)
+               on_missing: :unrelate
+             )
     end
   end
 
@@ -67,6 +100,40 @@ defmodule Mv.Membership.Member do
     validate present(:last_name)
     validate present(:email)
 
+    # Prevent linking to a user that already has a member
+    # This validation prevents "stealing" users from other members by checking
+    # if the target user is already linked to a different member
+    # This is necessary because manage_relationship's on_match: :error only checks
+    # if the user is already linked to THIS specific member, not ANY member
+    validate fn changeset, _context ->
+      user_arg = Ash.Changeset.get_argument(changeset, :user)
+
+      if user_arg && user_arg[:id] do
+        user_id = user_arg[:id]
+        current_member_id = changeset.data.id
+
+        # Check the current state of the user in the database
+        case Ash.get(Mv.Accounts.User, user_id) do
+          # User is free to be linked
+          {:ok, %{member_id: nil}} ->
+            :ok
+
+          # User already linked to this member (update scenario)
+          {:ok, %{member_id: ^current_member_id}} ->
+            :ok
+
+          {:ok, %{member_id: _other_member_id}} ->
+            # User is linked to a different member - prevent "stealing"
+            {:error, field: :user, message: "User is already linked to another member"}
+
+          {:error, _} ->
+            {:error, field: :user, message: "User not found"}
+        end
+      else
+        :ok
+      end
+    end
+
     # Birth date not in the future
     validate compare(:birth_date, less_than_or_equal_to: &Date.utc_today/0),
       where: [present(:birth_date)],
@@ -170,5 +237,9 @@ defmodule Mv.Membership.Member do
 
   relationships do
     has_many :properties, Mv.Membership.Property
+    # 1:1 relationship - Member can optionally have one User
+    # This references the User's member_id attribute
+    # The relationship is optional (allow_nil? true by default)
+    has_one :user, Mv.Accounts.User
   end
 end