🐛 fix(postgres-connection): 修复无postgres库时连接失败并支持默认连接库配置

- PostgreSQL 空 database 时按 postgres、template1、用户名同名库回退连接
- 移除后端对 database=postgres 的硬编码写死逻辑
- 连接弹窗新增 PostgreSQL 默认连接数据库（可选）配置项
- refs #120

frontend/src/components/ConnectionModal.tsx

@@ -1061,6 +1061,7 @@ const ConnectionModal: React.FC<{
           });
       } else if (type !== 'custom') {
           form.setFieldsValue({
+              database: '',
               port: defaultPort,
               mysqlTopology: 'single',
               mongoTopology: 'single',
@@ -1199,6 +1200,7 @@ const ConnectionModal: React.FC<{
             type: 'mysql',
             host: 'localhost',
             port: 3306,
+            database: '',
             user: 'root',
             useSSH: false,
             sshPort: 22,
@@ -1338,6 +1340,16 @@ const ConnectionModal: React.FC<{
             )}
         </div>
 
+        {(dbType === 'postgres' || dbType === 'kingbase' || dbType === 'highgo' || dbType === 'vastbase') && (
+        <Form.Item
+            name="database"
+            label="默认连接数据库（可选）"
+            help="留空会自动尝试 postgres、template1、与当前用户名同名数据库"
+        >
+            <Input placeholder="例如：appdb" />
+        </Form.Item>
+        )}
+
         {(dbType === 'mysql' || dbType === 'mariadb' || dbType === 'diros' || dbType === 'sphinx') && (
         <>
             <Form.Item name="mysqlTopology" label="连接模式">

internal/app/app.go

@@ -82,10 +82,6 @@ func getCacheKey(config connection.ConnectionConfig) string {
 	if !config.UseProxy {
 		config.Proxy = connection.ProxyConfig{}
 	}
-	// 保持与驱动默认一致，避免同一连接被重复缓存
-	if config.Type == "postgres" && config.Database == "" {
-		config.Database = "postgres"
-	}
 
 	b, _ := json.Marshal(config)
 	sum := sha256.Sum256(b)

internal/app/methods_db.go

@@ -190,9 +190,6 @@ func (a *App) RenameDatabase(config connection.ConnectionConfig, oldName string,
 			return connection.QueryResult{Success: false, Message: "当前连接正在使用目标数据库，请先连接到其他数据库后再重命名"}
 		}
 		runConfig := config
-		if strings.TrimSpace(runConfig.Database) == "" {
-			runConfig.Database = "postgres"
-		}
 		dbInst, err := a.getDatabase(runConfig)
 		if err != nil {
 			return connection.QueryResult{Success: false, Message: err.Error()}
@@ -228,9 +225,6 @@ func (a *App) DropDatabase(config connection.ConnectionConfig, dbName string) co
 			return connection.QueryResult{Success: false, Message: "当前连接正在使用目标数据库，请先连接到其他数据库后再删除"}
 		}
 		runConfig = config
-		if strings.TrimSpace(runConfig.Database) == "" {
-			runConfig.Database = "postgres"
-		}
 		sql = fmt.Sprintf("DROP DATABASE %s", quoteIdentByType(dbType, dbName))
 	default:
 		return connection.QueryResult{Success: false, Message: fmt.Sprintf("当前数据源(%s)暂不支持删除数据库", dbType)}

internal/db/postgres_connect_test.go

@@ -0,0 +1,48 @@
+package db
+
+import (
+	"reflect"
+	"testing"
+
+	"GoNavi-Wails/internal/connection"
+)
+
+func TestResolvePostgresConnectDatabases_ExplicitDatabase(t *testing.T) {
+	cfg := connection.ConnectionConfig{
+		Type:     "postgres",
+		Database: "analytics",
+		User:     "app_user",
+	}
+
+	got := resolvePostgresConnectDatabases(cfg)
+	want := []string{"analytics"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("unexpected databases, got=%v want=%v", got, want)
+	}
+}
+
+func TestResolvePostgresConnectDatabases_FallbackOrder(t *testing.T) {
+	cfg := connection.ConnectionConfig{
+		Type: "postgres",
+		User: "app_user",
+	}
+
+	got := resolvePostgresConnectDatabases(cfg)
+	want := []string{"postgres", "template1", "app_user"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("unexpected databases, got=%v want=%v", got, want)
+	}
+}
+
+func TestResolvePostgresConnectDatabases_DeduplicateUserDefault(t *testing.T) {
+	cfg := connection.ConnectionConfig{
+		Type: "postgres",
+		User: "postgres",
+	}
+
+	got := resolvePostgresConnectDatabases(cfg)
+	want := []string{"postgres", "template1"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("unexpected databases, got=%v want=%v", got, want)
+	}
+}

internal/db/postgres_impl.go

@@ -24,6 +24,30 @@ type PostgresDB struct {
 	forwarder   *ssh.LocalForwarder // Store SSH tunnel forwarder
 }
 
+func resolvePostgresConnectDatabases(config connection.ConnectionConfig) []string {
+	explicit := strings.TrimSpace(config.Database)
+	if explicit != "" {
+		return []string{explicit}
+	}
+
+	candidates := []string{"postgres", "template1", strings.TrimSpace(config.User)}
+	seen := make(map[string]struct{}, len(candidates))
+	result := make([]string, 0, len(candidates))
+	for _, name := range candidates {
+		trimmed := strings.TrimSpace(name)
+		if trimmed == "" {
+			continue
+		}
+		normalized := strings.ToLower(trimmed)
+		if _, exists := seen[normalized]; exists {
+			continue
+		}
+		seen[normalized] = struct{}{}
+		result = append(result, trimmed)
+	}
+	return result
+}
+
 func (p *PostgresDB) getDSN(config connection.ConnectionConfig) string {
 	// postgres://user:password@host:port/dbname?sslmode=disable
 	dbname := config.Database
@@ -53,8 +77,23 @@ func (p *PostgresDB) Connect(config connection.ConnectionConfig) error {
 		return fmt.Errorf("%s", reason)
 	}
 
-	var dsn string
-	var err error
+	runConfig := config
+	p.pingTimeout = getConnectTimeout(config)
+
+	cleanupOnFailure := true
+	defer func() {
+		if !cleanupOnFailure {
+			return
+		}
+		if p.conn != nil {
+			_ = p.conn.Close()
+			p.conn = nil
+		}
+		if p.forwarder != nil {
+			_ = p.forwarder.Close()
+			p.forwarder = nil
+		}
+	}()
 
 	if config.UseSSH {
 		// Create SSH tunnel with local port forwarding
@@ -83,24 +122,44 @@ func (p *PostgresDB) Connect(config connection.ConnectionConfig) error {
 		localConfig.Port = port
 		localConfig.UseSSH = false // Disable SSH flag for DSN generation
 
-		dsn = p.getDSN(localConfig)
+		runConfig = localConfig
 		logger.Infof("PostgreSQL 通过本地端口转发连接：%s -> %s:%d", forwarder.LocalAddr, config.Host, config.Port)
-	} else {
-		dsn = p.getDSN(config)
 	}
 
-	db, err := sql.Open("postgres", dsn)
-	if err != nil {
-		return fmt.Errorf("打开数据库连接失败：%w", err)
-	}
-	p.conn = db
-	p.pingTimeout = getConnectTimeout(config)
+	attemptDBs := resolvePostgresConnectDatabases(runConfig)
+	var failures []string
+	for _, dbName := range attemptDBs {
+		attemptConfig := runConfig
+		attemptConfig.Database = dbName
+		dsn := p.getDSN(attemptConfig)
 
-	// Force verification
-	if err := p.Ping(); err != nil {
-		return fmt.Errorf("连接建立后验证失败：%w", err)
+		dbConn, err := sql.Open("postgres", dsn)
+		if err != nil {
+			failures = append(failures, fmt.Sprintf("数据库=%s 打开连接失败: %v", dbName, err))
+			continue
+		}
+		p.conn = dbConn
+
+		// Force verification
+		if err := p.Ping(); err != nil {
+			failures = append(failures, fmt.Sprintf("数据库=%s 验证失败: %v", dbName, err))
+			_ = dbConn.Close()
+			p.conn = nil
+			continue
+		}
+
+		if strings.TrimSpace(config.Database) == "" && !strings.EqualFold(dbName, "postgres") {
+			logger.Infof("PostgreSQL 自动选择连接数据库：%s", dbName)
+		}
+
+		cleanupOnFailure = false
+		return nil
 	}
-	return nil
+
+	if len(failures) == 0 {
+		return fmt.Errorf("连接建立后验证失败：未找到可用的连接数据库")
+	}
+	return fmt.Errorf("连接建立后验证失败：%s", strings.Join(failures, "；"))
 }
 
 func (p *PostgresDB) Close() error {