migrate.go

// Copyright 2019-present Facebook Inc. All rights reserved.
// This source code is licensed under the Apache 2.0 license found
// in the LICENSE file in the root directory of this source tree.

package schema

import (
	"context"
	"crypto/md5"
	"errors"
	"fmt"
	"math"

	"ariga.io/atlas/sql/migrate"
	"ariga.io/atlas/sql/schema"
	"entgo.io/ent/dialect"
	"entgo.io/ent/dialect/sql"
	"entgo.io/ent/schema/field"
)

const (
	// TypeTable defines the table name holding the type information.
	TypeTable = "ent_types"
	// MaxTypes defines the max number of types can be created when
	// defining universal ids. The left 16-bits are reserved.
	MaxTypes = math.MaxUint16
)

// MigrateOption allows for managing schema configuration using functional options.
type MigrateOption func(*Migrate)

// WithGlobalUniqueID sets the universal ids options to the migration.
// Defaults to false.
func WithGlobalUniqueID(b bool) MigrateOption {
	return func(m *Migrate) {
		m.universalID = b
	}
}

// WithDropColumn sets the columns dropping option to the migration.
// Defaults to false.
func WithDropColumn(b bool) MigrateOption {
	return func(m *Migrate) {
		m.dropColumns = b
	}
}

// WithDropIndex sets the indexes dropping option to the migration.
// Defaults to false.
func WithDropIndex(b bool) MigrateOption {
	return func(m *Migrate) {
		m.dropIndexes = b
	}
}

// WithFixture sets the foreign-key renaming option to the migration when upgrading
// ent from v0.1.0 (issue-#285). Defaults to false.
func WithFixture(b bool) MigrateOption {
	return func(m *Migrate) {
		m.withFixture = b
	}
}

// WithForeignKeys enables creating foreign-key in ddl. Defaults to true.
func WithForeignKeys(b bool) MigrateOption {
	return func(m *Migrate) {
		m.withForeignKeys = b
	}
}

// WithHooks adds a list of hooks to the schema migration.
func WithHooks(hooks ...Hook) MigrateOption {
	return func(m *Migrate) {
		m.hooks = append(m.hooks, hooks...)
	}
}

type (
	// Creator is the interface that wraps the Create method.
	Creator interface {
		// Create creates the given tables in the database. See Migrate.Create for more details.
		Create(context.Context, ...*Table) error
	}

	// The CreateFunc type is an adapter to allow the use of ordinary function as Creator.
	// If f is a function with the appropriate signature, CreateFunc(f) is a Creator that calls f.
	CreateFunc func(context.Context, ...*Table) error

	// Hook defines the "create middleware". A function that gets a Creator and returns a Creator.
	// For example:
	//
	//	hook := func(next schema.Creator) schema.Creator {
	//		return schema.CreateFunc(func(ctx context.Context, tables ...*schema.Table) error {
	//			fmt.Println("Tables:", tables)
	//			return next.Create(ctx, tables...)
	//		})
	//	}
	//
	Hook func(Creator) Creator
)

// Create calls f(ctx, tables...).
func (f CreateFunc) Create(ctx context.Context, tables ...*Table) error {
	return f(ctx, tables...)
}

// Migrate runs the migrations logic for the SQL dialects.
type Migrate struct {
	sqlDialect
	universalID     bool          // global unique ids.
	dropColumns     bool          // drop deleted columns.
	dropIndexes     bool          // drop deleted indexes.
	withFixture     bool          // with fks rename fixture.
	withForeignKeys bool          // with foreign keys
	atlas           *atlasOptions // migrate with atlas.
	typeRanges      []string      // types order by their range.
	hooks           []Hook        // hooks to apply before creation
	typeStore       typeStore
}

// NewMigrate create a migration structure for the given SQL driver.
func NewMigrate(d dialect.Driver, opts ...MigrateOption) (*Migrate, error) {
	m := &Migrate{withForeignKeys: true, atlas: &atlasOptions{}}
	for _, opt := range opts {
		opt(m)
	}
	switch d.Dialect() {
	case dialect.MySQL:
		m.sqlDialect = &MySQL{Driver: d}
	case dialect.SQLite:
		m.sqlDialect = &SQLite{Driver: d, WithForeignKeys: m.withForeignKeys}
	case dialect.Postgres:
		m.sqlDialect = &Postgres{Driver: d}
	default:
		return nil, fmt.Errorf("sql/schema: unsupported dialect %q", d.Dialect())
	}
	m.typeStore = &dbTypeStore{m.sqlDialect}
	if err := m.setupAtlas(); err != nil {
		return nil, err
	}
	return m, nil
}

// Create creates all schema resources in the database. It works in an "append-only"
// mode, which means, it only creates tables, appends columns to tables or modifies column types.
//
// Column can be modified by turning into a NULL from NOT NULL, or having a type conversion not
// resulting data altering. From example, changing varchar(255) to varchar(120) is invalid, but
// changing varchar(120) to varchar(255) is valid. For more info, see the convert function below.
//
// Note that SQLite dialect does not support (this moment) the "append-only" mode describe above,
// since it's used only for testing.
func (m *Migrate) Create(ctx context.Context, tables ...*Table) error {
	for _, t := range tables {
		m.setupTable(t)
	}
	var creator Creator = CreateFunc(m.create)
	if m.atlas.enabled {
		creator = CreateFunc(m.atCreate)
	}
	for i := len(m.hooks) - 1; i >= 0; i-- {
		creator = m.hooks[i](creator)
	}
	return creator.Create(ctx, tables...)
}

// Diff compares the state read from the connected database with the state defined by Ent.
// Changes will be written to migration files by the configured Planner.
func (m *Migrate) Diff(ctx context.Context, tables ...*Table) error {
	return m.NamedDiff(ctx, "changes", tables...)
}

// NamedDiff compares the state read from the connected database with the state defined by Ent.
// Changes will be written to migration files by the configured Planner.
func (m *Migrate) NamedDiff(ctx context.Context, name string, tables ...*Table) error {
	if m.atlas.dir == nil {
		return errors.New("no migration directory given")
	}
	opts := []migrate.PlannerOption{
		migrate.WithFormatter(m.atlas.fmt),
	}
	if m.atlas.genSum {
		// Validate the migration directory before proceeding.
		if err := migrate.Validate(m.atlas.dir); err != nil {
			return fmt.Errorf("validating migration directory: %w", err)
		}
	} else {
		opts = append(opts, migrate.DisableChecksum())
	}
	if err := m.init(ctx, m); err != nil {
		return err
	}
	if m.universalID {
		if err := m.types(ctx, m); err != nil {
			return err
		}
		m.atlas.diff = append(m.atlas.diff, func(next Differ) Differ {
			return DiffFunc(func(current, desired *schema.Schema) ([]schema.Change, error) {
				// Make sure the TypeTable exists.
				exists, err := m.tableExist(ctx, m, TypeTable)
				if err != nil {
					return nil, err
				}
				if !exists {
					var (
						at = schema.NewTable(TypeTable)
						et = NewTable(TypeTable).
							AddPrimary(&Column{Name: "id", Type: field.TypeUint, Increment: true}).
							AddColumn(&Column{Name: "type", Type: field.TypeString, Unique: true})
					)
					m.atTable(et, at)
					if err := m.aColumns(m, et, at); err != nil {
						return nil, err
					}
					desired.Tables = append(desired.Tables, at)
				}
				return next.Diff(current, desired)
			})
		})
	}
	plan, err := m.atDiff(ctx, m, name, tables...)
	if err != nil {
		return err
	}
	if m.universalID {
		// Add the required entries to the TypeTable.
		for _, t := range m.typeStore.(*dirTypeStore).newTypes {
			plan.Changes = append(plan.Changes, &migrate.Change{
				Cmd:     m.atTypeRangeSQL(t),
				Comment: fmt.Sprintf(`add pk range for "%s" table`, t),
			})
		}
		// We have written a file. Reset the types-counter.
		m.typeStore.(*dirTypeStore).newTypes = nil
	}
	// Skip if the plan has no changes.
	if len(plan.Changes) == 0 {
		return nil
	}
	return migrate.NewPlanner(nil, m.atlas.dir, opts...).WritePlan(plan)
}

func (m *Migrate) create(ctx context.Context, tables ...*Table) error {
	tx, err := m.Tx(ctx)
	if err != nil {
		return err
	}
	if err := m.init(ctx, tx); err != nil {
		return rollback(tx, err)
	}
	if m.universalID {
		if err := m.types(ctx, tx); err != nil {
			return rollback(tx, err)
		}
	}
	if err := m.txCreate(ctx, tx, tables...); err != nil {
		return rollback(tx, err)
	}
	return tx.Commit()
}

func (m *Migrate) txCreate(ctx context.Context, tx dialect.Tx, tables ...*Table) error {
	for _, t := range tables {
		switch exist, err := m.tableExist(ctx, tx, t.Name); {
		case err != nil:
			return err
		case exist:
			curr, err := m.table(ctx, tx, t.Name)
			if err != nil {
				return err
			}
			if err := m.verify(ctx, tx, curr); err != nil {
				return err
			}
			if err := m.fixture(ctx, tx, curr, t); err != nil {
				return err
			}
			change, err := m.changeSet(curr, t)
			if err != nil {
				return fmt.Errorf("creating changeset for %q: %w", t.Name, err)
			}
			if err := m.apply(ctx, tx, t.Name, change); err != nil {
				return err
			}
		default: // !exist
			query, args := m.tBuilder(t).Query()
			if err := tx.Exec(ctx, query, args, nil); err != nil {
				return fmt.Errorf("create table %q: %w", t.Name, err)
			}
			// If global unique identifier is enabled and it's not
			// a relation table, allocate a range for the table pk.
			if m.universalID && len(t.PrimaryKey) == 1 {
				if err := m.allocPKRange(ctx, tx, t); err != nil {
					return err
				}
			}
			// indexes.
			for _, idx := range t.Indexes {
				query, args := m.addIndex(idx, t.Name).Query()
				if err := tx.Exec(ctx, query, args, nil); err != nil {
					return fmt.Errorf("create index %q: %w", idx.Name, err)
				}
			}
		}
	}
	if !m.withForeignKeys {
		return nil
	}
	// Create foreign keys after tables were created/altered,
	// because circular foreign-key constraints are possible.
	for _, t := range tables {
		if len(t.ForeignKeys) == 0 {
			continue
		}
		fks := make([]*ForeignKey, 0, len(t.ForeignKeys))
		for _, fk := range t.ForeignKeys {
			exist, err := m.fkExist(ctx, tx, fk.Symbol)
			if err != nil {
				return err
			}
			if !exist {
				fks = append(fks, fk)
			}
		}
		if len(fks) == 0 {
			continue
		}
		b := sql.Dialect(m.Dialect()).AlterTable(t.Name)
		for _, fk := range fks {
			b.AddForeignKey(fk.DSL())
		}
		query, args := b.Query()
		if err := tx.Exec(ctx, query, args, nil); err != nil {
			return fmt.Errorf("create foreign keys for %q: %w", t.Name, err)
		}
	}
	return nil
}

// apply applies changes on the given table.
func (m *Migrate) apply(ctx context.Context, tx dialect.Tx, table string, change *changes) error {
	// Constraints should be dropped before dropping columns, because if a column
	// is a part of multi-column constraints (like, unique index), ALTER TABLE
	// might fail if the intermediate state violates the constraints.
	if m.dropIndexes {
		if pr, ok := m.sqlDialect.(preparer); ok {
			if err := pr.prepare(ctx, tx, change, table); err != nil {
				return err
			}
		}
		for _, idx := range change.index.drop {
			if err := m.dropIndex(ctx, tx, idx, table); err != nil {
				return fmt.Errorf("drop index of table %q: %w", table, err)
			}
		}
	}
	var drop []*Column
	if m.dropColumns {
		drop = change.column.drop
	}
	queries := m.alterColumns(table, change.column.add, change.column.modify, drop)
	// If there's actual action to execute on ALTER TABLE.
	for i := range queries {
		query, args := queries[i].Query()
		if err := tx.Exec(ctx, query, args, nil); err != nil {
			return fmt.Errorf("alter table %q: %w", table, err)
		}
	}
	for _, idx := range change.index.add {
		query, args := m.addIndex(idx, table).Query()
		if err := tx.Exec(ctx, query, args, nil); err != nil {
			return fmt.Errorf("create index %q: %w", table, err)
		}
	}
	return nil
}

// changes to apply on existing table.
type changes struct {
	// column changes.
	column struct {
		add    []*Column
		drop   []*Column
		modify []*Column
	}
	// index changes.
	index struct {
		add  Indexes
		drop Indexes
	}
}

// dropColumn returns the dropped column by name (if any).
func (c *changes) dropColumn(name string) (*Column, bool) {
	for _, col := range c.column.drop {
		if col.Name == name {
			return col, true
		}
	}
	return nil, false
}

// changeSet returns a changes object to be applied on existing table.
// It fails if one of the changes is invalid.
func (m *Migrate) changeSet(curr, new *Table) (*changes, error) {
	change := &changes{}
	// pks.
	if len(curr.PrimaryKey) != len(new.PrimaryKey) {
		return nil, fmt.Errorf("cannot change primary key for table: %q", curr.Name)
	}
	for i := range curr.PrimaryKey {
		if curr.PrimaryKey[i].Name != new.PrimaryKey[i].Name {
			return nil, fmt.Errorf("cannot change primary key for table: %q", curr.Name)
		}
	}
	// Add or modify columns.
	for _, c1 := range new.Columns {
		// Ignore primary keys.
		if c1.PrimaryKey() {
			continue
		}
		switch c2, ok := curr.column(c1.Name); {
		case !ok:
			change.column.add = append(change.column.add, c1)
		case !c2.Type.Valid():
			return nil, fmt.Errorf("invalid type %q for column %q", c2.typ, c2.Name)
		// Modify a non-unique column to unique.
		case c1.Unique && !c2.Unique:
			// Make sure the table does not have unique index for this column
			// before adding it to the changeset, because there are 2 ways to
			// configure uniqueness on ent.Field (using the Unique modifier or
			// adding rule on the Indexes option).
			if idx, ok := curr.index(c1.Name); !ok || !idx.Unique {
				change.index.add.append(&Index{
					Name:    c1.Name,
					Unique:  true,
					Columns: []*Column{c1},
					columns: []string{c1.Name},
				})
			}
		// Modify a unique column to non-unique.
		case !c1.Unique && c2.Unique:
			// If the uniqueness was defined on the Indexes option,
			// or was moved from the Unique modifier to the Indexes.
			if idx, ok := new.index(c1.Name); ok && idx.Unique {
				continue
			}
			idx, ok := curr.index(c2.Name)
			if !ok {
				return nil, fmt.Errorf("missing index to drop for unique column %q", c2.Name)
			}
			change.index.drop.append(idx)
		// Extending column types.
		case m.needsConversion(c2, c1):
			if !c2.ConvertibleTo(c1) {
				return nil, fmt.Errorf("changing column type for %q is invalid (%s != %s)", c1.Name, m.cType(c1), m.cType(c2))
			}
			fallthrough
		// Change nullability of a column.
		case c1.Nullable != c2.Nullable:
			change.column.modify = append(change.column.modify, c1)
		// Change default value.
		case c1.Default != nil && c2.Default == nil:
			change.column.modify = append(change.column.modify, c1)
		}
	}
	// Drop columns.
	for _, c1 := range curr.Columns {
		// If a column was dropped, multi-columns indexes that are associated with this column will
		// no longer behave the same. Therefore, these indexes should be dropped too. There's no need
		// to do it explicitly (here), because entc will remove them from the schema specification,
		// and they will be dropped in the block below.
		if _, ok := new.column(c1.Name); !ok {
			change.column.drop = append(change.column.drop, c1)
		}
	}
	// Add or modify indexes.
	for _, idx1 := range new.Indexes {
		switch idx2, ok := curr.index(idx1.Name); {
		case !ok:
			change.index.add.append(idx1)
		// Changing index cardinality require drop and create.
		case idx1.Unique != idx2.Unique:
			change.index.drop.append(idx2)
			change.index.add.append(idx1)
		default:
			im, ok := m.sqlDialect.(interface{ indexModified(old, new *Index) bool })
			// If the dialect supports comparing indexes.
			if ok && im.indexModified(idx2, idx1) {
				change.index.drop.append(idx2)
				change.index.add.append(idx1)
			}
		}
	}
	// Drop indexes.
	for _, idx := range curr.Indexes {
		if _, isFK := new.fk(idx.Name); !isFK && !new.hasIndex(idx.Name, idx.realname) {
			change.index.drop.append(idx)
		}
	}
	return change, nil
}

// fixture is a special migration code for renaming foreign-key columns (issue-#285).
func (m *Migrate) fixture(ctx context.Context, tx dialect.Tx, curr, new *Table) error {
	d, ok := m.sqlDialect.(fkRenamer)
	if !m.withFixture || !m.withForeignKeys || !ok {
		return nil
	}
	rename := make(map[string]*Index)
	for _, fk := range new.ForeignKeys {
		ok, err := m.fkExist(ctx, tx, fk.Symbol)
		if err != nil {
			return fmt.Errorf("checking foreign-key existence %q: %w", fk.Symbol, err)
		}
		if !ok {
			continue
		}
		column, err := m.fkColumn(ctx, tx, fk)
		if err != nil {
			return err
		}
		newcol := fk.Columns[0]
		if column == newcol.Name {
			continue
		}
		query, args := d.renameColumn(curr, &Column{Name: column}, newcol).Query()
		if err := tx.Exec(ctx, query, args, nil); err != nil {
			return fmt.Errorf("rename column %q: %w", column, err)
		}
		prev, ok := curr.column(column)
		if !ok {
			continue
		}
		// Find all indexes that ~maybe need to be renamed.
		for _, idx := range prev.indexes {
			switch _, ok := new.index(idx.Name); {
			// Ignore indexes that exist in the schema, PKs.
			case ok || idx.primary:
			// Index that was created implicitly for a unique
			// column needs to be renamed to the column name.
			case d.isImplicitIndex(idx, prev):
				idx2 := &Index{Name: newcol.Name, Unique: true, Columns: []*Column{newcol}}
				query, args := d.renameIndex(curr, idx, idx2).Query()
				if err := tx.Exec(ctx, query, args, nil); err != nil {
					return fmt.Errorf("rename index %q: %w", prev.Name, err)
				}
				idx.Name = idx2.Name
			default:
				rename[idx.Name] = idx
			}
		}
		// Update the name of the loaded column, so `changeSet` won't create it.
		prev.Name = newcol.Name
	}
	// Go over the indexes that need to be renamed
	// and find their ~identical in the new schema.
	for _, idx := range rename {
	Find:
		// Find its ~identical in the new schema, and rename it
		// if it doesn't exist.
		for _, idx2 := range new.Indexes {
			if _, ok := curr.index(idx2.Name); ok {
				continue
			}
			if idx.sameAs(idx2) {
				query, args := d.renameIndex(curr, idx, idx2).Query()
				if err := tx.Exec(ctx, query, args, nil); err != nil {
					return fmt.Errorf("rename index %q: %w", idx.Name, err)
				}
				idx.Name = idx2.Name
				break Find
			}
		}
	}
	return nil
}

// verify that the auto-increment counter is correct for table with universal-id support.
func (m *Migrate) verify(ctx context.Context, tx dialect.Tx, t *Table) error {
	vr, ok := m.sqlDialect.(verifyRanger)
	if !ok || !m.universalID {
		return nil
	}
	id := indexOf(m.typeRanges, t.Name)
	if id == -1 {
		return nil
	}
	return vr.verifyRange(ctx, tx, t, int64(id<<32))
}

// types loads the type list from the type store.
func (m *Migrate) types(ctx context.Context, tx dialect.ExecQuerier) (err error) {
	m.typeRanges, err = m.typeStore.load(ctx, tx)
	return
}

func (m *Migrate) allocPKRange(ctx context.Context, conn dialect.ExecQuerier, t *Table) error {
	r, err := m.pkRange(ctx, conn, t)
	if err != nil {
		return err
	}
	return m.setRange(ctx, conn, t, r)
}

func (m *Migrate) pkRange(ctx context.Context, conn dialect.ExecQuerier, t *Table) (int64, error) {
	id := indexOf(m.typeRanges, t.Name)
	// If the table re-created, re-use its range from
	// the past. Otherwise, allocate a new id-range.
	if id == -1 {
		if len(m.typeRanges) > MaxTypes {
			return 0, fmt.Errorf("max number of types exceeded: %d", MaxTypes)
		}
		if err := m.typeStore.add(ctx, conn, t.Name); err != nil {
			return 0, fmt.Errorf("store type range: %w", err)
		}
		id = len(m.typeRanges)
		m.typeRanges = append(m.typeRanges, t.Name)
	}
	return int64(id << 32), nil
}

// fkColumn returns the column name of a foreign-key.
func (m *Migrate) fkColumn(ctx context.Context, tx dialect.Tx, fk *ForeignKey) (string, error) {
	t1 := sql.Table("INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS t1").Unquote().As("t1")
	t2 := sql.Table("INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS t2").Unquote().As("t2")
	query, args := sql.Dialect(m.Dialect()).
		Select("column_name").
		From(t1).
		Join(t2).
		On(t1.C("constraint_name"), t2.C("constraint_name")).
		Where(sql.And(
			sql.EQ(t2.C("constraint_type"), sql.Raw("'FOREIGN KEY'")),
			m.sqlDialect.(fkRenamer).matchSchema(t2.C("table_schema")),
			m.sqlDialect.(fkRenamer).matchSchema(t1.C("table_schema")),
			sql.EQ(t2.C("constraint_name"), fk.Symbol),
		)).
		Query()
	rows := &sql.Rows{}
	if err := tx.Query(ctx, query, args, rows); err != nil {
		return "", fmt.Errorf("reading foreign-key %q column: %w", fk.Symbol, err)
	}
	defer rows.Close()
	column, err := sql.ScanString(rows)
	if err != nil {
		return "", fmt.Errorf("scanning foreign-key %q column: %w", fk.Symbol, err)
	}
	return column, nil
}

// setup ensures the table is configured properly, like table columns
// are linked to their indexes, and PKs columns are defined.
func (m *Migrate) setupTable(t *Table) {
	if t.columns == nil {
		t.columns = make(map[string]*Column, len(t.Columns))
	}
	for _, c := range t.Columns {
		t.columns[c.Name] = c
	}
	for _, idx := range t.Indexes {
		idx.Name = m.symbol(idx.Name)
		for _, c := range idx.Columns {
			c.indexes.append(idx)
		}
	}
	for _, pk := range t.PrimaryKey {
		c := t.columns[pk.Name]
		c.Key = PrimaryKey
		pk.Key = PrimaryKey
	}
	for _, fk := range t.ForeignKeys {
		fk.Symbol = m.symbol(fk.Symbol)
		for i := range fk.Columns {
			fk.Columns[i].foreign = fk
		}
	}
}

// symbol makes sure the symbol length is not longer than the maxlength in the dialect.
func (m *Migrate) symbol(name string) string {
	size := 64
	if m.Dialect() == dialect.Postgres {
		size = 63
	}
	if len(name) <= size {
		return name
	}
	return fmt.Sprintf("%s_%x", name[:size-33], md5.Sum([]byte(name)))
}

// rollback calls to tx.Rollback and wraps the given error with the rollback error if occurred.
func rollback(tx dialect.Tx, err error) error {
	err = fmt.Errorf("sql/schema: %w", err)
	if rerr := tx.Rollback(); rerr != nil {
		err = fmt.Errorf("%w: %v", err, rerr)
	}
	return err
}

// exist checks if the given COUNT query returns a value >= 1.
func exist(ctx context.Context, conn dialect.ExecQuerier, query string, args ...interface{}) (bool, error) {
	rows := &sql.Rows{}
	if err := conn.Query(ctx, query, args, rows); err != nil {
		return false, fmt.Errorf("reading schema information %w", err)
	}
	defer rows.Close()
	n, err := sql.ScanInt(rows)
	if err != nil {
		return false, err
	}
	return n > 0, nil
}

func indexOf(a []string, s string) int {
	for i := range a {
		if a[i] == s {
			return i
		}
	}
	return -1
}

type sqlDialect interface {
	atBuilder
	dialect.Driver
	init(context.Context, dialect.ExecQuerier) error
	table(context.Context, dialect.Tx, string) (*Table, error)
	tableExist(context.Context, dialect.ExecQuerier, string) (bool, error)
	fkExist(context.Context, dialect.Tx, string) (bool, error)
	setRange(context.Context, dialect.ExecQuerier, *Table, int64) error
	dropIndex(context.Context, dialect.Tx, *Index, string) error
	// table, column and index builder per dialect.
	cType(*Column) string
	tBuilder(*Table) *sql.TableBuilder
	addIndex(*Index, string) *sql.IndexBuilder
	alterColumns(table string, add, modify, drop []*Column) sql.Queries
	needsConversion(*Column, *Column) bool
}

type preparer interface {
	prepare(context.Context, dialect.Tx, *changes, string) error
}

// fkRenamer is used by the fixture migration (to solve #285),
// and it's implemented by the different dialects for renaming FKs.
type fkRenamer interface {
	matchSchema(...string) *sql.Predicate
	isImplicitIndex(*Index, *Column) bool
	renameIndex(*Table, *Index, *Index) sql.Querier
	renameColumn(*Table, *Column, *Column) sql.Querier
}

// verifyRanger wraps the method for verifying global-id range correctness.
type verifyRanger interface {
	verifyRange(context.Context, dialect.Tx, *Table, int64) error
}

// typeStore wraps methods for loading and storing pk range information for types.
type typeStore interface {
	load(context.Context, dialect.ExecQuerier) ([]string, error)
	add(context.Context, dialect.ExecQuerier, string) error
}

// dbTypeStore stores and read pk information in a database table.
// This is the "old" behaviour before the typeStore interface was added.
type dbTypeStore struct {
	drv sqlDialect
}

// load the types from the database. If the table does not exist, it will be created.
func (s *dbTypeStore) load(ctx context.Context, conn dialect.ExecQuerier) ([]string, error) {
	exists, err := s.drv.tableExist(ctx, conn, TypeTable)
	if err != nil {
		return nil, err
	}
	if !exists {
		t := NewTable(TypeTable).
			AddPrimary(&Column{Name: "id", Type: field.TypeUint, Increment: true}).
			AddColumn(&Column{Name: "type", Type: field.TypeString, Unique: true})
		query, args := s.drv.tBuilder(t).Query()
		if err := conn.Exec(ctx, query, args, nil); err != nil {
			return nil, fmt.Errorf("create types table: %w", err)
		}
		return nil, nil
	}
	rows := &sql.Rows{}
	query, args := sql.Dialect(s.drv.Dialect()).
		Select("type").From(sql.Table(TypeTable)).OrderBy(sql.Asc("id")).Query()
	if err := conn.Query(ctx, query, args, rows); err != nil {
		return nil, fmt.Errorf("query types table: %w", err)
	}
	defer rows.Close()
	var types []string
	return types, sql.ScanSlice(rows, &types)
}

// add a new type entry to the database table. since load is called first,
// there is no need to check for the tables' existence.
func (s *dbTypeStore) add(ctx context.Context, conn dialect.ExecQuerier, t string) error {
	query, args := sql.Dialect(s.drv.Dialect()).
		Insert(TypeTable).Columns("type").Values(t).Query()
	if err := conn.Exec(ctx, query, args, nil); err != nil {
		return fmt.Errorf("insert into ent_types: %w", err)
	}
	return nil
}

var _ typeStore = (*dbTypeStore)(nil)