feat(custom-field): add join_description attribute for GDPR join-form labels

lib/membership/custom_field.ex

@@ -12,6 +12,8 @@ defmodule Mv.Membership.CustomField do
   - `slug` - URL-friendly, immutable identifier automatically generated from name (e.g., "phone-mobile")
   - `value_type` - Data type constraint (`:string`, `:integer`, `:boolean`, `:date`, `:email`). Immutable after creation.
   - `description` - Optional human-readable description
+  - `join_description` - Optional label shown for this field on the public join form
+    (e.g., a GDPR confirmation text); supports inline external links. Falls back to `name` when nil.
   - `required` - If true, all members must have this custom field (future feature)
   - `show_in_overview` - If true, this custom field will be displayed in the member overview table and can be sorted
 
@@ -61,7 +63,14 @@ defmodule Mv.Membership.CustomField do
   end
 
   actions do
-    default_accept [:name, :value_type, :description, :required, :show_in_overview]
+    default_accept [
+      :name,
+      :value_type,
+      :description,
+      :join_description,
+      :required,
+      :show_in_overview
+    ]
 
     read :read do
       primary? true
@@ -69,13 +78,13 @@ defmodule Mv.Membership.CustomField do
     end
 
     create :create do
-      accept [:name, :value_type, :description, :required, :show_in_overview]
+      accept [:name, :value_type, :description, :join_description, :required, :show_in_overview]
       change Mv.Membership.Changes.GenerateSlug
       validate string_length(:slug, min: 1)
     end
 
     update :update do
-      accept [:name, :description, :required, :show_in_overview]
+      accept [:name, :description, :join_description, :required, :show_in_overview]
       require_atomic? false
 
       validate fn changeset, _context ->
@@ -139,6 +148,15 @@ defmodule Mv.Membership.CustomField do
         trim?: true
       ]
 
+    attribute :join_description, :string,
+      allow_nil?: true,
+      public?: true,
+      description: "Label shown for this field on the public join form; supports external links",
+      constraints: [
+        max_length: 1000,
+        trim?: true
+      ]
+
     attribute :required, :boolean,
       default: false,
       allow_nil?: false

priv/repo/migrations/20260603000531_add_join_description_to_custom_fields.exs

@@ -0,0 +1,21 @@
+defmodule Mv.Repo.Migrations.AddJoinDescriptionToCustomFields do
+  @moduledoc """
+  Updates resources based on their most recent snapshots.
+
+  This file was autogenerated with `mix ash_postgres.generate_migrations`
+  """
+
+  use Ecto.Migration
+
+  def up do
+    alter table(:custom_fields) do
+      add :join_description, :text
+    end
+  end
+
+  def down do
+    alter table(:custom_fields) do
+      remove :join_description
+    end
+  end
+end

priv/resource_snapshots/repo/custom_fields/20260603000204.json

@@ -0,0 +1,145 @@
+{
+  "attributes": [
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"gen_random_uuid()\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": true,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "id",
+      "type": "uuid"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "name",
+      "type": "text"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "slug",
+      "type": "text"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "value_type",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "description",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "join_description",
+      "type": "text"
+    },
+    {
+      "allow_nil?": false,
+      "default": "false",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "required",
+      "type": "boolean"
+    },
+    {
+      "allow_nil?": false,
+      "default": "true",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "show_in_overview",
+      "type": "boolean"
+    }
+  ],
+  "base_filter": null,
+  "check_constraints": [],
+  "create_table_options": null,
+  "custom_indexes": [],
+  "custom_statements": [],
+  "has_create_action": true,
+  "hash": "2600667D140A2A846F9A848ACEFCADA1F1206950B38EF407B0BB13816E508A2A",
+  "identities": [
+    {
+      "all_tenants?": false,
+      "base_filter": null,
+      "index_name": "custom_fields_unique_name_index",
+      "keys": [
+        {
+          "type": "atom",
+          "value": "name"
+        }
+      ],
+      "name": "unique_name",
+      "nils_distinct?": true,
+      "where": null
+    },
+    {
+      "all_tenants?": false,
+      "base_filter": null,
+      "index_name": "custom_fields_unique_slug_index",
+      "keys": [
+        {
+          "type": "atom",
+          "value": "slug"
+        }
+      ],
+      "name": "unique_slug",
+      "nils_distinct?": true,
+      "where": null
+    }
+  ],
+  "multitenancy": {
+    "attribute": null,
+    "global": null,
+    "strategy": null
+  },
+  "repo": "Elixir.Mv.Repo",
+  "schema": null,
+  "table": "custom_fields"
+}

test/membership/custom_field_validation_test.exs

@@ -159,6 +159,61 @@ defmodule Mv.Membership.CustomFieldValidationTest do
     end
   end
 
+  describe "join_description" do
+    test "persists join_description when set", %{actor: actor} do
+      assert {:ok, custom_field} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "dsgvo_field",
+                 value_type: :boolean,
+                 join_description: "hereby I confirm the GDPR"
+               })
+               |> Ash.create(actor: actor)
+
+      assert custom_field.join_description == "hereby I confirm the GDPR"
+    end
+
+    test "defaults to nil when not given", %{actor: actor} do
+      assert {:ok, custom_field} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "no_join_desc",
+                 value_type: :boolean
+               })
+               |> Ash.create(actor: actor)
+
+      assert custom_field.join_description == nil
+    end
+
+    test "rejects join_description longer than 1000 characters", %{actor: actor} do
+      assert {:error, changeset} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "too_long_join_desc",
+                 value_type: :boolean,
+                 join_description: String.duplicate("a", 1001)
+               })
+               |> Ash.create(actor: actor)
+
+      assert [%{field: :join_description, message: message}] = changeset.errors
+      assert message =~ "max" or message =~ "length" or message =~ "1000"
+    end
+
+    test "is writable via the update action", %{actor: actor} do
+      {:ok, custom_field} =
+        CustomField
+        |> Ash.Changeset.for_create(:create, %{name: "updatable", value_type: :boolean})
+        |> Ash.create(actor: actor)
+
+      assert {:ok, updated} =
+               custom_field
+               |> Ash.Changeset.for_update(:update, %{join_description: "Accept the GDPR"})
+               |> Ash.update(actor: actor)
+
+      assert updated.join_description == "Accept the GDPR"
+    end
+  end
+
   describe "name uniqueness" do
     test "rejects duplicate names", %{actor: actor} do
       assert {:ok, _} =