From 21c7aa31ea1f5431192d994f5afb09dad49e8389 Mon Sep 17 00:00:00 2001
From: Masahiko AMANO <hiko-19@ya.ru>
Date: Thu, 11 Jun 2026 23:31:59 +0300
Subject: [PATCH] fix(backend): store an empty tag colour as NULL

The PATCH "clear colour" path sent an empty string, which violates the
hex CHECK constraint and never falls back to the category colour. Map ''
to NULL via NULLIF in the tag insert/update so a cleared or omitted
colour is stored as NULL.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 backend/internal/db/postgres/tag_repo.go    |  4 +--
 backend/internal/integration/server_test.go | 35 +++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/backend/internal/db/postgres/tag_repo.go b/backend/internal/db/postgres/tag_repo.go
index 232c8ba..329db6e 100644
--- a/backend/internal/db/postgres/tag_repo.go
+++ b/backend/internal/db/postgres/tag_repo.go
@@ -272,7 +272,7 @@ func (r *TagRepo) Create(ctx context.Context, t *domain.Tag) (*domain.Tag, error
 	const query = `
 WITH ins AS (
     INSERT INTO data.tags (name, notes, color, category_id, metadata, creator_id, is_public)
-    VALUES ($1, $2, $3, $4, $5, $6, $7)
+    VALUES ($1, $2, NULLIF($3, ''), $4, $5, $6, $7)
     RETURNING *
 )
 SELECT
@@ -321,7 +321,7 @@ WITH upd AS (
     UPDATE data.tags SET
         name        = $2,
         notes       = $3,
-        color       = $4,
+        color       = NULLIF($4, ''),
         category_id = $5,
         metadata    = COALESCE($6, metadata),
         is_public   = $7
diff --git a/backend/internal/integration/server_test.go b/backend/internal/integration/server_test.go
index a5819f6..fded83f 100644
--- a/backend/internal/integration/server_test.go
+++ b/backend/internal/integration/server_test.go
@@ -891,6 +891,41 @@ func TestRecordPoolView(t *testing.T) {
 	require.Equal(t, http.StatusNotFound, resp.StatusCode, resp.String())
 }
 
+// TestTagColorOptional verifies a tag can be created without a colour (stored as
+// NULL rather than the colour input's default) and that an existing colour can
+// be cleared back to none.
+func TestTagColorOptional(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping integration test in short mode")
+	}
+
+	h := setupSuite(t)
+	adminToken := h.login("admin", "admin")
+
+	// Created without a colour → color is null.
+	resp := h.doJSON("POST", "/tags", map[string]any{"name": "plain"}, adminToken)
+	require.Equal(t, http.StatusCreated, resp.StatusCode, resp.String())
+	var plain map[string]any
+	resp.decode(t, &plain)
+	assert.Nil(t, plain["color"], "tag created without a colour should have null color")
+
+	// Created with a colour → kept verbatim.
+	resp = h.doJSON("POST", "/tags", map[string]any{"name": "red", "color": "aabbcc"}, adminToken)
+	require.Equal(t, http.StatusCreated, resp.StatusCode, resp.String())
+	var red map[string]any
+	resp.decode(t, &red)
+	assert.Equal(t, "aabbcc", red["color"])
+	redID := red["id"].(string)
+
+	// Clearing the colour (color: null) must store NULL — an empty string would
+	// violate the hex CHECK constraint and fail the update.
+	resp = h.doJSON("PATCH", "/tags/"+redID, map[string]any{"color": nil}, adminToken)
+	require.Equal(t, http.StatusOK, resp.StatusCode, resp.String())
+	var cleared map[string]any
+	resp.decode(t, &cleared)
+	assert.Nil(t, cleared["color"], "cleared colour should be null")
+}
+
 // TestBulkTagAutoRule verifies the bulk add path also applies then_tags.
 func TestBulkTagAutoRule(t *testing.T) {
 	if testing.Short() {