check param and add comment

errors.go

@@ -23,6 +23,8 @@ var (
 	ErrModelValueRequired = errors.New("model value required")
 	// ErrModelAccessibleFieldsRequired model accessible fields required
 	ErrModelAccessibleFieldsRequired = errors.New("model accessible fields required")
+	// ErrSubQueryRequired sub query required
+	ErrSubQueryRequired = errors.New("sub query required")
 	// ErrInvalidData unsupported data
 	ErrInvalidData = errors.New("unsupported data")
 	// ErrUnsupportedDriver unsupported driver

migrator.go

@@ -30,9 +30,9 @@ func (db *DB) AutoMigrate(dst ...interface{}) error {
 
 // ViewOption view option
 type ViewOption struct {
-	Replace     bool   // CREATE [ OR REPLACE ]
+	Replace     bool   // If true, exec `CREATE`. If false, exec `CREATE OR REPLACE`
-	CheckOption string // WITH [ CASCADED | LOCAL ] CHECK OPTION
+	CheckOption string // optional. e.g. `WITH [ CASCADED | LOCAL ] CHECK OPTION`
-	Query       *DB
+	Query       *DB    // required subquery.
 }
 
 // ColumnType column type interface

migrator/migrator.go

@@ -557,8 +557,23 @@ func (m Migrator) ColumnTypes(value interface{}) ([]gorm.ColumnType, error) {
 	return columnTypes, execErr
 }
 
-// CreateView create view
+// CreateView create view from Query in gorm.ViewOption.
+// Query in gorm.ViewOption is a [subquery]
+//
+//	// CREATE VIEW `user_view` AS SELECT * FROM `users` WHERE age > 20
+//	q := DB.Model(&User{}).Where("age > ?", 20)
+//	DB.Debug().Migrator().CreateView("user_view", gorm.ViewOption{Query: q})
+//
+//	// CREATE OR REPLACE VIEW `users_view` AS SELECT * FROM `users` WITH CHECK OPTION
+//	q := DB.Model(&User{})
+//	DB.Debug().Migrator().CreateView("user_view", gorm.ViewOption{Query: q, Replace: true, CheckOption: "WITH CHECK OPTION"})
+//
+// [subquery]: https://gorm.io/docs/advanced_query.html#SubQuery
 func (m Migrator) CreateView(name string, option gorm.ViewOption) error {
+	if option.Query == nil {
+		return gorm.ErrSubQueryRequired
+	}
+
 	sql := new(strings.Builder)
 	sql.WriteString("CREATE ")
 	if option.Replace {
@@ -574,7 +589,7 @@ func (m Migrator) CreateView(name string, option gorm.ViewOption) error {
 		sql.WriteString(" ")
 		sql.WriteString(option.CheckOption)
 	}
-	return m.DB.Exec(sql.String()).Error
+	return m.DB.Exec(m.Explain(sql.String(), m.DB.Statement.Vars...)).Error
 }
 
 // DropView drop view

tests/migrate_test.go

@@ -1513,6 +1513,10 @@ func TestMigrateIgnoreRelations(t *testing.T) {
 func TestMigrateView(t *testing.T) {
 	DB.Save(GetUser("joins-args-db", Config{Pets: 2}))
 
+	if err := DB.Migrator().CreateView("invalid_users_pets", gorm.ViewOption{Query: nil}); err != gorm.ErrSubQueryRequired {
+		t.Fatalf("no view should be created, got %v", err)
+	}
+
 	query := DB.Model(&User{}).
 		Select("users.id as users_id, users.name as users_name, pets.id as pets_id, pets.name as pets_name").
 		Joins("inner join pets on pets.user_id = users.id")
@@ -1529,4 +1533,12 @@ func TestMigrateView(t *testing.T) {
 	if err := DB.Migrator().DropView("users_pets"); err != nil {
 		t.Fatalf("Failed to drop view, got %v", err)
 	}
+
+	query = DB.Model(&User{}).Where("age > ?", 20)
+	if err := DB.Migrator().CreateView("users_view", gorm.ViewOption{Query: query}); err != nil {
+		t.Fatalf("Failed to crate view, got %v", err)
+	}
+	if err := DB.Migrator().DropView("users_view"); err != nil {
+		t.Fatalf("Failed to drop view, got %v", err)
+	}
 }