Create and drop view (#6097)

* create view

* add comment

* fix test

* 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
+	Replace     bool   // If true, exec `CREATE`. If false, exec `CREATE OR REPLACE`
-	CheckOption string
+	CheckOption string // optional. e.g. `WITH [ CASCADED | LOCAL ] CHECK OPTION`
-	Query       *DB
+	Query       *DB    // required subquery.
 }
 
 // ColumnType column type interface

migrator/migrator.go

@@ -557,14 +557,44 @@ 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 {
-	return gorm.ErrNotImplemented
+	if option.Query == nil {
+		return gorm.ErrSubQueryRequired
+	}
+
+	sql := new(strings.Builder)
+	sql.WriteString("CREATE ")
+	if option.Replace {
+		sql.WriteString("OR REPLACE ")
+	}
+	sql.WriteString("VIEW ")
+	m.QuoteTo(sql, name)
+	sql.WriteString(" AS ")
+
+	m.DB.Statement.AddVar(sql, option.Query)
+
+	if option.CheckOption != "" {
+		sql.WriteString(" ")
+		sql.WriteString(option.CheckOption)
+	}
+	return m.DB.Exec(m.Explain(sql.String(), m.DB.Statement.Vars...)).Error
 }
 
 // DropView drop view
 func (m Migrator) DropView(name string) error {
-	return gorm.ErrNotImplemented
+	return m.DB.Exec("DROP VIEW IF EXISTS ?", clause.Table{Name: name}).Error
 }
 
 func buildConstraint(constraint *schema.Constraint) (sql string, results []interface{}) {

tests/migrate_test.go

@@ -1509,3 +1509,36 @@ func TestMigrateIgnoreRelations(t *testing.T) {
 		t.Errorf("RelationModel2 should not be migrated")
 	}
 }
+
+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")
+
+	if err := DB.Migrator().CreateView("users_pets", gorm.ViewOption{Query: query}); err != nil {
+		t.Fatalf("Failed to crate view, got %v", err)
+	}
+
+	var count int64
+	if err := DB.Table("users_pets").Count(&count).Error; err != nil {
+		t.Fatalf("should found created view")
+	}
+
+	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)
+	}
+}