From 97dd4bd9c7421426118cb9af3f50512d7a96b7c6 Mon Sep 17 00:00:00 2001
From: Denis Shevchenko <denis.shevchenko@outlook.com>
Date: Wed, 5 Aug 2026 10:20:45 +0300
Subject: [PATCH] fix(mermaid): render column definitions as comments

---
 target/mermaid/mermaid.go          | 19 +++++++++++++++++-
 target/mermaid/mermaid_test.go     |  6 ++----
 target/mermaid/schema.tmpl         |  2 +-
 target/mermaid/testdata/schema.mmd | 32 +++++++++++++++---------------
 4 files changed, 37 insertions(+), 22 deletions(-)

diff --git a/target/mermaid/mermaid.go b/target/mermaid/mermaid.go
index 97e2643..2b83029 100644
--- a/target/mermaid/mermaid.go
+++ b/target/mermaid/mermaid.go
@@ -6,6 +6,7 @@ import (
 	"context"
 	"embed"
 	"fmt"
+	"strings"
 	"text/template"
 
 	"github.com/holydocs/dberd"
@@ -27,7 +28,9 @@ type Target struct {
 
 // NewTarget creates a new Mermaid JS diagram formatter instance.
 func NewTarget() (*Target, error) {
-	tmpl, err := template.ParseFS(templateFS, "schema.tmpl")
+	tmpl, err := template.New("schema.tmpl").Funcs(template.FuncMap{
+		"mermaidComment": mermaidComment,
+	}).ParseFS(templateFS, "schema.tmpl")
 	if err != nil {
 		return nil, fmt.Errorf("parsing template: %w", err)
 	}
@@ -37,6 +40,20 @@ func NewTarget() (*Target, error) {
 	}, nil
 }
 
+func mermaidComment(definition, comment string) string {
+	parts := make([]string, 0, 2)
+
+	for _, value := range []string{definition, comment} {
+		value = strings.Join(strings.Fields(value), " ")
+		value = strings.ReplaceAll(value, `"`, "'")
+		if value != "" {
+			parts = append(parts, value)
+		}
+	}
+
+	return strings.Join(parts, "; ")
+}
+
 // Capabilities returns target capabilities.
 func (t *Target) Capabilities() dberd.TargetCapabilities {
 	return dberd.TargetCapabilities{
diff --git a/target/mermaid/mermaid_test.go b/target/mermaid/mermaid_test.go
index 69c39f3..19f46c6 100644
--- a/target/mermaid/mermaid_test.go
+++ b/target/mermaid/mermaid_test.go
@@ -10,10 +10,8 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-var (
-	//go:embed testdata/schema.mmd
-	testSchema []byte
-)
+//go:embed testdata/schema.mmd
+var testSchema []byte
 
 func TestFormatSchema(t *testing.T) {
 	t.Parallel()
diff --git a/target/mermaid/schema.tmpl b/target/mermaid/schema.tmpl
index 5de70ef..0659163 100644
--- a/target/mermaid/schema.tmpl
+++ b/target/mermaid/schema.tmpl
@@ -3,7 +3,7 @@ erDiagram
 {{- range .Tables }}
     "{{ .Name }}" {
         {{- range .Columns }}
-        {{ .Definition }} {{ .Name }}{{ if .IsPrimary }} PK{{ end }}
+        column {{ .Name }}{{ if .IsPrimary }} PK{{ end }}{{ with mermaidComment .Definition .Comment }} "{{ . }}"{{ end }}
         {{- end }}
     }
 {{- end }}
diff --git a/target/mermaid/testdata/schema.mmd b/target/mermaid/testdata/schema.mmd
index 55a48e2..34908f9 100644
--- a/target/mermaid/testdata/schema.mmd
+++ b/target/mermaid/testdata/schema.mmd
@@ -1,27 +1,27 @@
 erDiagram
     "public.users" {
-        INT8 NOT NULL id PK
-        VARCHAR(255) NOT NULL name
-        VARCHAR(255) NOT NULL email
-        TIMESTAMP DEFAULT current_timestamp() created_at
+        column id PK "INT8 NOT NULL"
+        column name "VARCHAR(255) NOT NULL"
+        column email "VARCHAR(255) NOT NULL; User email address"
+        column created_at "TIMESTAMP DEFAULT current_timestamp()"
     }
     "public.roles" {
-        INT8 NOT NULL id PK
-        VARCHAR(50) NOT NULL name
-        STRING description
-        TIMESTAMP DEFAULT current_timestamp() created_at
+        column id PK "INT8 NOT NULL"
+        column name "VARCHAR(50) NOT NULL"
+        column description "STRING; Role description and permissions"
+        column created_at "TIMESTAMP DEFAULT current_timestamp()"
     }
     "public.user_roles" {
-        INT8 NOT NULL user_id PK
-        INT8 NOT NULL role_id PK
-        TIMESTAMP DEFAULT current_timestamp() assigned_at
+        column user_id PK "INT8 NOT NULL"
+        column role_id PK "INT8 NOT NULL"
+        column assigned_at "TIMESTAMP DEFAULT current_timestamp()"
     }
     "public.posts" {
-        INT8 NOT NULL id PK
-        INT8 NOT NULL user_id
-        VARCHAR(255) NOT NULL title
-        STRING content
-        TIMESTAMP DEFAULT current_timestamp() created_at
+        column id PK "INT8 NOT NULL"
+        column user_id "INT8 NOT NULL"
+        column title "VARCHAR(255) NOT NULL"
+        column content "STRING"
+        column created_at "TIMESTAMP DEFAULT current_timestamp()"
     }
     "public.user_roles" }o--|| "public.roles" : "role_id -> id"
     "public.user_roles" }o--|| "public.users" : "user_id -> id"