MVP: 按 07 风格重写前端 + Go 后端落地（长文/短文、编辑器、后台管理）

backend/internal/db/db.go

@@ -0,0 +1,101 @@
+// Package db opens a *sql.DB for either SQLite or PostgreSQL and rewrites
+// the shared `?` placeholders into PostgreSQL's `$n` form.
+package db
+
+import (
+	"database/sql"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	_ "github.com/lib/pq"
+	_ "modernc.org/sqlite"
+)
+
+type Dialect int
+
+const (
+	SQLite Dialect = iota
+	Postgres
+)
+
+type DB struct {
+	*sql.DB
+	Dialect Dialect
+}
+
+func Open(driver, dsn string) (*DB, error) {
+	var d Dialect
+	switch driver {
+	case "sqlite":
+		d = SQLite
+		if err := os.MkdirAll(filepath.Dir(dsn), 0o755); err != nil {
+			return nil, err
+		}
+		dsn = addSQLiteParams(dsn)
+	case "postgres":
+		d = Postgres
+	default:
+		return nil, fmt.Errorf("unsupported driver %q", driver)
+	}
+
+	pool, err := sql.Open(driverName(driver), dsn)
+	if err != nil {
+		return nil, err
+	}
+	if d == SQLite {
+		// SQLite is single-writer; keep a small pool to avoid "database is locked".
+		pool.SetMaxOpenConns(1)
+	} else {
+		pool.SetMaxOpenConns(10)
+	}
+	if err := pool.Ping(); err != nil {
+		return nil, fmt.Errorf("connect %s: %w", driver, err)
+	}
+	return &DB{DB: pool, Dialect: d}, nil
+}
+
+func driverName(driver string) string {
+	if driver == "postgres" {
+		return "postgres"
+	}
+	return "sqlite"
+}
+
+func addSQLiteParams(dsn string) string {
+	if strings.HasPrefix(dsn, "file:") || strings.Contains(dsn, "?") {
+		return dsn
+	}
+	return dsn + "?_pragma=busy_timeout(5000)&_pragma=journal_mode(WAL)&_pragma=foreign_keys(1)"
+}
+
+// Rebind converts `?` placeholders to `$1..$n` on PostgreSQL.
+func (d *DB) Rebind(q string) string {
+	if d.Dialect != Postgres {
+		return q
+	}
+	var b strings.Builder
+	b.Grow(len(q) + 8)
+	n := 0
+	for _, r := range q {
+		if r == '?' {
+			n++
+			b.WriteString("$")
+			b.WriteString(fmt.Sprint(n))
+			continue
+		}
+		b.WriteRune(r)
+	}
+	return b.String()
+}
+
+func (d *DB) Q(q string) string { return d.Rebind(q) }
+
+// AutoInc returns the column definition for an auto-incrementing primary key.
+func (d *DB) AutoInc() string {
+	if d.Dialect == Postgres {
+		return "BIGSERIAL PRIMARY KEY"
+	}
+	return "INTEGER PRIMARY KEY AUTOINCREMENT"
+}

backend/internal/db/db_test.go

@@ -0,0 +1,28 @@
+package db
+
+import "testing"
+
+func TestRebind(t *testing.T) {
+	sqlite := &DB{Dialect: SQLite}
+	pg := &DB{Dialect: Postgres}
+
+	q := "SELECT * FROM posts WHERE kind = ? AND status = ? LIMIT ? OFFSET ?"
+
+	if got := sqlite.Rebind(q); got != q {
+		t.Errorf("sqlite must keep ? placeholders, got %q", got)
+	}
+
+	want := "SELECT * FROM posts WHERE kind = $1 AND status = $2 LIMIT $3 OFFSET $4"
+	if got := pg.Rebind(q); got != want {
+		t.Errorf("postgres rebind:\n got %q\nwant %q", got, want)
+	}
+}
+
+func TestAutoInc(t *testing.T) {
+	if got := (&DB{Dialect: SQLite}).AutoInc(); got != "INTEGER PRIMARY KEY AUTOINCREMENT" {
+		t.Errorf("sqlite autoincrement = %q", got)
+	}
+	if got := (&DB{Dialect: Postgres}).AutoInc(); got != "BIGSERIAL PRIMARY KEY" {
+		t.Errorf("postgres autoincrement = %q", got)
+	}
+}