Implement rename column operation

pkg/migrations/op_common.go

@@ -11,13 +11,14 @@ import (
 type OpName string
 
 const (
-	OpNameCreateTable OpName = "create_table"
-	OpNameRenameTable OpName = "rename_table"
-	OpNameDropTable   OpName = "drop_table"
-	OpNameAddColumn   OpName = "add_column"
-	OpNameDropColumn  OpName = "drop_column"
-	OpNameCreateIndex OpName = "create_index"
-	OpNameDropIndex   OpName = "drop_index"
+	OpNameCreateTable  OpName = "create_table"
+	OpNameRenameTable  OpName = "rename_table"
+	OpNameDropTable    OpName = "drop_table"
+	OpNameAddColumn    OpName = "add_column"
+	OpNameDropColumn   OpName = "drop_column"
+	OpNameCreateIndex  OpName = "create_index"
+	OpNameDropIndex    OpName = "drop_index"
+	OpNameRenameColumn OpName = "rename_column"
 )
 
 func TemporaryName(name string) string {
@@ -88,6 +89,9 @@ func (v *Operations) UnmarshalJSON(data []byte) error {
 		case OpNameDropColumn:
 			item = &OpDropColumn{}
 
+		case OpNameRenameColumn:
+			item = &OpRenameColumn{}
+
 		case OpNameCreateIndex:
 			item = &OpCreateIndex{}
 
@@ -141,6 +145,9 @@ func (v Operations) MarshalJSON() ([]byte, error) {
 		case *OpDropColumn:
 			opName = OpNameDropColumn
 
+		case *OpRenameColumn:
+			opName = OpNameRenameColumn
+
 		case *OpCreateIndex:
 			opName = OpNameCreateIndex
 

pkg/migrations/op_rename_column.go

@@ -0,0 +1,56 @@
+package migrations
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/lib/pq"
+
+	"pg-roll/pkg/schema"
+)
+
+type OpRenameColumn struct {
+	Table string `json:"table"`
+	From  string `json:"from"`
+	To    string `json:"to"`
+}
+
+var _ Operation = (*OpRenameColumn)(nil)
+
+func (o *OpRenameColumn) Start(ctx context.Context, conn *sql.DB, schemaName string, stateSchema string, s *schema.Schema) error {
+	table := s.GetTable(o.Table)
+	table.RenameColumn(o.From, o.To)
+	return nil
+}
+
+func (o *OpRenameColumn) Complete(ctx context.Context, conn *sql.DB) error {
+	// rename the column in the underlying table
+	_, err := conn.ExecContext(ctx, fmt.Sprintf("ALTER TABLE IF EXISTS %s RENAME COLUMN %s TO %s",
+		pq.QuoteIdentifier(o.Table),
+		pq.QuoteIdentifier(o.From),
+		pq.QuoteIdentifier(o.To)))
+	return err
+}
+
+func (o *OpRenameColumn) Rollback(ctx context.Context, conn *sql.DB) error {
+	// no-op
+	return nil
+}
+
+func (o *OpRenameColumn) Validate(ctx context.Context, s *schema.Schema) error {
+	table := s.GetTable(o.Table)
+	if table == nil {
+		return TableDoesNotExistError{Name: o.Table}
+	}
+
+	if table.GetColumn(o.From) == nil {
+		return ColumnDoesNotExistError{Table: o.Table, Name: o.From}
+	}
+
+	if table.GetColumn(o.To) != nil {
+		return ColumnAlreadyExistsError{Table: o.Table, Name: o.From}
+	}
+
+	return nil
+}

pkg/schema/schema.go

@@ -106,3 +106,8 @@ func (t *Table) AddColumn(name string, c Column) {
 func (t *Table) RemoveColumn(column string) {
 	delete(t.Columns, column)
 }
+
+func (t *Table) RenameColumn(from, to string) {
+	t.Columns[to] = t.Columns[from]
+	delete(t.Columns, from)
+}