Add 'alter column' operation to combine some existing operations (#91)

Introduce a new `alter_column` operation to combine existing operations
that work on columns.

The following operation types should be combined into one:

- [x] Change column type
- [x] Rename column
- [ ] Add `CHECK` constraint
- [ ] Add foreign key constraint
- [ ] Make column `NOT NULL`
- [ ] Add unique constraint

This PR implements the first two operations in the list, leaving the
rest for a later PR.

The new `alter_column` migrations look like:

```json
{
  "name": "18_change_column_type",
  "operations": [
    {
      "alter_column": {
        "table": "reviews",
        "column": "rating",
        "type": "integer",
        "up": "CAST(rating AS integer)",
        "down": "CAST(rating AS text)"
      }
    }
  ]
}

```
and

```json
{
  "name": "13_rename_column",
  "operations": [
    {
      "alter_column": {
        "table": "employees",
        "column": "role",
        "name": "job_title"
      }
    }
  ]
}
```

examples/13_rename_column.json

@@ -2,10 +2,10 @@
   "name": "13_rename_column",
   "operations": [
     {
-      "rename_column": {
+      "alter_column": {
         "table": "employees",
-        "from": "role",
-        "to": "jobTitle"
+        "column": "role",
+        "name": "job_title"
       }
     }
   ]

examples/18_change_column_type.json

@@ -2,7 +2,7 @@
   "name": "18_change_column_type",
   "operations": [
     {
-      "change_type": {
+      "alter_column": {
         "table": "reviews",
         "column": "rating",
         "type": "integer",

pkg/migrations/errors.go

@@ -99,3 +99,21 @@ func (e ColumnReferenceError) Error() string {
 		e.Table,
 		e.Err.Error())
 }
+
+type NoUpSQLAllowedError struct{}
+
+func (e NoUpSQLAllowedError) Error() string {
+	return "up SQL is not allowed for this operation"
+}
+
+type NoDownSQLAllowedError struct{}
+
+func (e NoDownSQLAllowedError) Error() string {
+	return "down SQL is not allowed for this operation"
+}
+
+type MultipleAlterColumnChangesError struct{}
+
+func (e MultipleAlterColumnChangesError) Error() string {
+	return "alter column operations require exactly one change"
+}

pkg/migrations/op_alter_column.go

@@ -0,0 +1,93 @@
+package migrations
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/xataio/pg-roll/pkg/schema"
+)
+
+type OpAlterColumn struct {
+	Table  string `json:"table"`
+	Column string `json:"column"`
+	Name   string `json:"name"`
+	Type   string `json:"type"`
+	Up     string `json:"up"`
+	Down   string `json:"down"`
+}
+
+var _ Operation = (*OpAlterColumn)(nil)
+
+func (o *OpAlterColumn) Start(ctx context.Context, conn *sql.DB, stateSchema string, s *schema.Schema) error {
+	op := o.innerOperation()
+
+	return op.Start(ctx, conn, stateSchema, s)
+}
+
+func (o *OpAlterColumn) Complete(ctx context.Context, conn *sql.DB) error {
+	op := o.innerOperation()
+
+	return op.Complete(ctx, conn)
+}
+
+func (o *OpAlterColumn) Rollback(ctx context.Context, conn *sql.DB) error {
+	op := o.innerOperation()
+
+	return op.Rollback(ctx, conn)
+}
+
+func (o *OpAlterColumn) Validate(ctx context.Context, s *schema.Schema) error {
+	op := o.innerOperation()
+
+	if !o.oneChange() {
+		return MultipleAlterColumnChangesError{}
+	}
+
+	if _, ok := op.(*OpRenameColumn); ok {
+		if o.Up != "" {
+			return NoUpSQLAllowedError{}
+		}
+		if o.Down != "" {
+			return NoDownSQLAllowedError{}
+		}
+	}
+
+	return op.Validate(ctx, s)
+}
+
+func (o *OpAlterColumn) innerOperation() Operation {
+	switch {
+	case o.Name != "":
+		return &OpRenameColumn{
+			Table: o.Table,
+			From:  o.Column,
+			To:    o.Name,
+		}
+
+	case o.Type != "":
+		return &OpChangeType{
+			Table:  o.Table,
+			Column: o.Column,
+			Type:   o.Type,
+			Up:     o.Up,
+			Down:   o.Down,
+		}
+	}
+	return nil
+}
+
+// oneChange ensures that the 'alter column' operation attempts to make
+// only one kind of change. For example, it should not attempt to rename a
+// column and change its type at the same time.
+func (o *OpAlterColumn) oneChange() bool {
+	fieldsSet := 0
+
+	if o.Name != "" {
+		fieldsSet++
+	}
+	if o.Type != "" {
+		fieldsSet++
+	}
+
+	return fieldsSet == 1
+}

pkg/migrations/op_alter_column_test.go

@@ -0,0 +1,122 @@
+package migrations_test
+
+import (
+	"testing"
+
+	"github.com/xataio/pg-roll/pkg/migrations"
+)
+
+func TestAlterColumnValidation(t *testing.T) {
+	t.Parallel()
+
+	createTablesMigration := migrations.Migration{
+		Name: "01_add_tables",
+		Operations: migrations.Operations{
+			&migrations.OpCreateTable{
+				Name: "users",
+				Columns: []migrations.Column{
+					{
+						Name:       "id",
+						Type:       "serial",
+						PrimaryKey: true,
+					},
+					{
+						Name: "name",
+						Type: "text",
+					},
+				},
+			},
+			&migrations.OpCreateTable{
+				Name: "posts",
+				Columns: []migrations.Column{
+					{
+						Name:       "id",
+						Type:       "serial",
+						PrimaryKey: true,
+					},
+					{
+						Name: "title",
+						Type: "text",
+					},
+					{
+						Name: "user_id",
+						Type: "integer",
+					},
+				},
+			},
+		},
+	}
+
+	ExecuteTests(t, TestCases{
+		{
+			name: "column rename: no up SQL allowed",
+			migrations: []migrations.Migration{
+				createTablesMigration,
+				{
+					Name: "01_alter_column",
+					Operations: migrations.Operations{
+						&migrations.OpAlterColumn{
+							Table:  "posts",
+							Column: "title",
+							Name:   "renamed_title",
+							Up:     "some up sql",
+						},
+					},
+				},
+			},
+			wantStartErr: migrations.NoUpSQLAllowedError{},
+		},
+		{
+			name: "column rename: no down SQL allowed",
+			migrations: []migrations.Migration{
+				createTablesMigration,
+				{
+					Name: "01_alter_column",
+					Operations: migrations.Operations{
+						&migrations.OpAlterColumn{
+							Table:  "posts",
+							Column: "title",
+							Name:   "renamed_title",
+							Down:   "some down sql",
+						},
+					},
+				},
+			},
+			wantStartErr: migrations.NoDownSQLAllowedError{},
+		},
+		{
+			name: "cant make no changes",
+			migrations: []migrations.Migration{
+				createTablesMigration,
+				{
+					Name: "01_alter_column",
+					Operations: migrations.Operations{
+						&migrations.OpAlterColumn{
+							Table:  "posts",
+							Column: "title",
+						},
+					},
+				},
+			},
+			wantStartErr: migrations.MultipleAlterColumnChangesError{},
+		},
+		{
+			name: "only one change at at time",
+			migrations: []migrations.Migration{
+				createTablesMigration,
+				{
+					Name: "01_alter_column",
+					Operations: migrations.Operations{
+						&migrations.OpAlterColumn{
+							Table:  "posts",
+							Column: "title",
+							Name:   "renamed_title",
+							Type:   "varchar(255)",
+						},
+					},
+				},
+			},
+			wantStartErr: migrations.MultipleAlterColumnChangesError{},
+		},
+	})
+}

pkg/migrations/op_change_type_test.go

@@ -46,7 +46,7 @@ func TestChangeColumnType(t *testing.T) {
 			{
 				Name: "02_change_type",
 				Operations: migrations.Operations{
-					&migrations.OpChangeType{
+					&migrations.OpAlterColumn{
 						Table:  "reviews",
 						Column: "rating",
 						Type:   "integer",
@@ -184,7 +184,7 @@ func TestChangeColumnTypeValidation(t *testing.T) {
 				{
 					Name: "02_change_type",
 					Operations: migrations.Operations{
-						&migrations.OpChangeType{
+						&migrations.OpAlterColumn{
 							Table:  "reviews",
 							Column: "rating",
 							Type:   "integer",
@@ -202,7 +202,7 @@ func TestChangeColumnTypeValidation(t *testing.T) {
 				{
 					Name: "02_change_type",
 					Operations: migrations.Operations{
-						&migrations.OpChangeType{
+						&migrations.OpAlterColumn{
 							Table:  "reviews",
 							Column: "rating",
 							Type:   "integer",
@@ -220,7 +220,7 @@ func TestChangeColumnTypeValidation(t *testing.T) {
 				{
 					Name: "02_change_type",
 					Operations: migrations.Operations{
-						&migrations.OpChangeType{
+						&migrations.OpAlterColumn{
 							Table:  "doesntexist",
 							Column: "rating",
 							Type:   "integer",
@@ -239,7 +239,7 @@ func TestChangeColumnTypeValidation(t *testing.T) {
 				{
 					Name: "02_change_type",
 					Operations: migrations.Operations{
-						&migrations.OpChangeType{
+						&migrations.OpAlterColumn{
 							Table:  "reviews",
 							Column: "doesntexist",
 							Type:   "integer",

pkg/migrations/op_common.go

@@ -11,20 +11,23 @@ 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"
+	OpNameAlterColumn OpName = "alter_column"
+	OpNameCreateIndex OpName = "create_index"
+	OpNameDropIndex   OpName = "drop_index"
+	OpRawSQLName      OpName = "sql"
+
+	// Internal operation types used by `alter_column`
 	OpNameRenameColumn       OpName = "rename_column"
 	OpNameSetUnique          OpName = "set_unique"
 	OpNameSetNotNull         OpName = "set_not_null"
 	OpNameSetForeignKey      OpName = "set_foreign_key"
 	OpNameSetCheckConstraint OpName = "set_check_constraint"
 	OpNameChangeType         OpName = "change_type"
-	OpRawSQLName             OpName = "sql"
 )
 
 func TemporaryName(name string) string {
@@ -95,8 +98,8 @@ func (v *Operations) UnmarshalJSON(data []byte) error {
 		case OpNameDropColumn:
 			item = &OpDropColumn{}
 
-		case OpNameRenameColumn:
-			item = &OpRenameColumn{}
+		case OpNameAlterColumn:
+			item = &OpAlterColumn{}
 
 		case OpNameCreateIndex:
 			item = &OpCreateIndex{}
@@ -116,9 +119,6 @@ func (v *Operations) UnmarshalJSON(data []byte) error {
 		case OpNameSetCheckConstraint:
 			item = &OpSetCheckConstraint{}
 
-		case OpNameChangeType:
-			item = &OpChangeType{}
-
 		case OpRawSQLName:
 			item = &OpRawSQL{}
 
@@ -181,8 +181,8 @@ func OperationName(op Operation) OpName {
 	case *OpDropColumn:
 		return OpNameDropColumn
 
-	case *OpRenameColumn:
-		return OpNameRenameColumn
+	case *OpAlterColumn:
+		return OpNameAlterColumn
 
 	case *OpCreateIndex:
 		return OpNameCreateIndex
@@ -202,9 +202,6 @@ func OperationName(op Operation) OpName {
 	case *OpSetCheckConstraint:
 		return OpNameSetCheckConstraint
 
-	case *OpChangeType:
-		return OpNameChangeType
-
 	case *OpRawSQL:
 		return OpRawSQLName
 

pkg/migrations/op_rename_column_test.go

@@ -37,10 +37,10 @@ func TestRenameColumn(t *testing.T) {
 			{
 				Name: "02_rename_column",
 				Operations: migrations.Operations{
-					&migrations.OpRenameColumn{
-						Table: "users",
-						From:  "username",
-						To:    "name",
+					&migrations.OpAlterColumn{
+						Table:  "users",
+						Column: "username",
+						Name:   "name",
 					},
 				},
 			},