Gorm:gorm.io/gorm源码

Gorm之gorm.io/gorm源码

注：本文是基于Windos系统上 gorm.io/gorm@v1.23.4进行讲解

1.gorm.Open函数

// Open initialize db session based on dialector
//返回：gorm.DB结构体
func Open(dialector Dialector, opts ...Option) (db *DB, err error) {
	config := &Config{}

	sort.Slice(opts, func(i, j int) bool {
		_, isConfig := opts[i].(*Config)
		_, isConfig2 := opts[j].(*Config)
		return isConfig && !isConfig2
	})

	for _, opt := range opts {
		if opt != nil {
			if applyErr := opt.Apply(config); applyErr != nil {
				return nil, applyErr
			}
			defer func(opt Option) {
				if errr := opt.AfterInitialize(db); errr != nil {
					err = errr
				}
			}(opt)
		}
	}

	if d, ok := dialector.(interface{ Apply(*Config) error }); ok {
		if err = d.Apply(config); err != nil {
			return
		}
	}

	if config.NamingStrategy == nil {
		config.NamingStrategy = schema.NamingStrategy{}
	}

	if config.Logger == nil {
		config.Logger = logger.Default
	}

	if config.NowFunc == nil {
		config.NowFunc = func() time.Time { return time.Now().Local() }
	}

	if dialector != nil {
		config.Dialector = dialector
	}

	if config.Plugins == nil {
		config.Plugins = map[string]Plugin{}
	}

	if config.cacheStore == nil {
		config.cacheStore = &sync.Map{}
	}

	db = &DB{Config: config, clone: 1}

	db.callbacks = initializeCallbacks(db)

	if config.ClauseBuilders == nil {
		config.ClauseBuilders = map[string]clause.ClauseBuilder{}
	}

	if config.Dialector != nil {
		err = config.Dialector.Initialize(db)
	}

	preparedStmt := &PreparedStmtDB{
		ConnPool:    db.ConnPool,
		Stmts:       map[string]Stmt{},
		Mux:         &sync.RWMutex{},
		PreparedSQL: make([]string, 0, 100),
	}
	db.cacheStore.Store(preparedStmtDBKey, preparedStmt)

	if config.PrepareStmt {
		db.ConnPool = preparedStmt
	}

	db.Statement = &Statement{
		DB:       db,
		ConnPool: db.ConnPool,
		Context:  context.Background(),
		Clauses:  map[string]clause.Clause{},
	}

	if err == nil && !config.DisableAutomaticPing {
		if pinger, ok := db.ConnPool.(interface{ Ping() error }); ok {
			err = pinger.Ping()
		}
	}

	if err != nil {
		config.Logger.Error(context.Background(), "failed to initialize database, got error %v", err)
	}

	return
}

2.gorm.Dialector接口

// Dialector GORM database dialector
type Dialector interface {
	Name() string
	Initialize(*DB) error
	Migrator(db *DB) Migrator
	DataTypeOf(*schema.Field) string
	DefaultValueOf(*schema.Field) clause.Expression
	BindVarTo(writer clause.Writer, stmt *Statement, v interface{})
	QuoteTo(clause.Writer, string)
	Explain(sql string, vars ...interface{}) string
}

3.gorm.Config结构体

// Config GORM config
type Config struct {
	// GORM perform single create, update, delete operations in transactions by default to ensure database data integrity
	// You can disable it by setting `SkipDefaultTransaction` to true
	SkipDefaultTransaction bool
	// NamingStrategy tables, columns naming strategy
	NamingStrategy schema.Namer
	// FullSaveAssociations full save associations
	FullSaveAssociations bool
	// Logger
	Logger logger.Interface
	// NowFunc the function to be used when creating a new timestamp
	NowFunc func() time.Time
	// DryRun generate sql without execute
	DryRun bool
	// PrepareStmt executes the given query in cached statement
	PrepareStmt bool
	// DisableAutomaticPing
	DisableAutomaticPing bool
	// DisableForeignKeyConstraintWhenMigrating
	DisableForeignKeyConstraintWhenMigrating bool
	// DisableNestedTransaction disable nested transaction
	DisableNestedTransaction bool
	// AllowGlobalUpdate allow global update
	AllowGlobalUpdate bool
	// QueryFields executes the SQL query with all fields of the table
	QueryFields bool
	// CreateBatchSize default create batch size
	CreateBatchSize int

	// ClauseBuilders clause builder
	ClauseBuilders map[string]clause.ClauseBuilder
	// ConnPool db conn pool
	ConnPool ConnPool
	// Dialector database dialector
	Dialector
	// Plugins registered plugins
	Plugins map[string]Plugin

	callbacks  *callbacks
	cacheStore *sync.Map
}

4.gorm.DB结构体

4.1gorm.DB结构体

// DB GORM DB definition
type DB struct {
	*Config      //gorm.Config结构体
	Error        error
	RowsAffected int64
	Statement    *Statement
	clone        int
}

4.2AutoMigrate方法

// AutoMigrate run auto migration for given models
func (db *DB) AutoMigrate(dst ...interface{}) error {
	return db.Migrator().AutoMigrate(dst...)
}

4.3Migrator方法

// Migrator returns migrator
func (db *DB) Migrator() Migrator {
	tx := db.getInstance()

	// apply scopes to migrator
	for len(tx.Statement.scopes) > 0 {
		scopes := tx.Statement.scopes
		tx.Statement.scopes = nil
		for _, scope := range scopes {
			tx = scope(tx)
		}
	}

	return tx.Dialector.Migrator(tx.Session(&Session{}))
}

4.4Create方法

// Create insert the value into database
func (db *DB) Create(value interface{}) (tx *DB) {
	if db.CreateBatchSize > 0 {
		return db.CreateInBatches(value, db.CreateBatchSize)
	}

	tx = db.getInstance()
	tx.Statement.Dest = value
	return tx.callbacks.Create().Execute(tx)
}

4.5CreateInBatches方法

// CreateInBatches insert the value in batches into database
func (db *DB) CreateInBatches(value interface{}, batchSize int) (tx *DB) {
	reflectValue := reflect.Indirect(reflect.ValueOf(value))

	switch reflectValue.Kind() {
	case reflect.Slice, reflect.Array:
		var rowsAffected int64
		tx = db.getInstance()

		callFc := func(tx *DB) error {
			// the reflection length judgment of the optimized value
			reflectLen := reflectValue.Len()
			for i := 0; i < reflectLen; i  = batchSize {
				ends := i   batchSize
				if ends > reflectLen {
					ends = reflectLen
				}

				subtx := tx.getInstance()
				subtx.Statement.Dest = reflectValue.Slice(i, ends).Interface()
				subtx.callbacks.Create().Execute(subtx)
				if subtx.Error != nil {
					return subtx.Error
				}
				rowsAffected  = subtx.RowsAffected
			}
			return nil
		}

		if tx.SkipDefaultTransaction {
			tx.AddError(callFc(tx.Session(&Session{})))
		} else {
			tx.AddError(tx.Transaction(callFc))
		}

		tx.RowsAffected = rowsAffected
	default:
		tx = db.getInstance()
		tx.Statement.Dest = value
		tx = tx.callbacks.Create().Execute(tx)
	}
	return
}

4.6Save方法

// Save update value in database, if the value doesn't have primary key, will insert it
func (db *DB) Save(value interface{}) (tx *DB) {
	tx = db.getInstance()
	tx.Statement.Dest = value

	reflectValue := reflect.Indirect(reflect.ValueOf(value))
	switch reflectValue.Kind() {
	case reflect.Slice, reflect.Array:
		if _, ok := tx.Statement.Clauses["ON CONFLICT"]; !ok {
			tx = tx.Clauses(clause.OnConflict{UpdateAll: true})
		}
		tx = tx.callbacks.Create().Execute(tx.Set("gorm:update_track_time", true))
	case reflect.Struct:
		if err := tx.Statement.Parse(value); err == nil && tx.Statement.Schema != nil {
			for _, pf := range tx.Statement.Schema.PrimaryFields {
				if _, isZero := pf.ValueOf(tx.Statement.Context, reflectValue); isZero {
					return tx.callbacks.Create().Execute(tx)
				}
			}
		}

		fallthrough
	default:
		selectedUpdate := len(tx.Statement.Selects) != 0
		// when updating, use all fields including those zero-value fields
		if !selectedUpdate {
			tx.Statement.Selects = append(tx.Statement.Selects, "*")
		}

		tx = tx.callbacks.Update().Execute(tx)

		if tx.Error == nil && tx.RowsAffected == 0 && !tx.DryRun && !selectedUpdate {
			result := reflect.New(tx.Statement.Schema.ModelType).Interface()
			if err := tx.Session(&Session{}).Take(result).Error; errors.Is(err, ErrRecordNotFound) {
				return tx.Create(value)
			}
		}
	}

	return
}

4.7First方法

// First find first record that match given conditions, order by primary key
func (db *DB) First(dest interface{}, conds ...interface{}) (tx *DB) {
	tx = db.Limit(1).Order(clause.OrderByColumn{
		Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey},
	})
	if len(conds) > 0 {
		if exprs := tx.Statement.BuildCondition(conds[0], conds[1:]...); len(exprs) > 0 {
			tx.Statement.AddClause(clause.Where{Exprs: exprs})
		}
	}
	tx.Statement.RaiseErrorOnNotFound = true
	tx.Statement.Dest = dest
	return tx.callbacks.Query().Execute(tx)
}

4.8Take方法

// Take return a record that match given conditions, the order will depend on the database implementation
func (db *DB) Take(dest interface{}, conds ...interface{}) (tx *DB) {
	tx = db.Limit(1)
	if len(conds) > 0 {
		if exprs := tx.Statement.BuildCondition(conds[0], conds[1:]...); len(exprs) > 0 {
			tx.Statement.AddClause(clause.Where{Exprs: exprs})
		}
	}
	tx.Statement.RaiseErrorOnNotFound = true
	tx.Statement.Dest = dest
	return tx.callbacks.Query().Execute(tx)
}

4.9Last方法

// Last find last record that match given conditions, order by primary key
func (db *DB) Last(dest interface{}, conds ...interface{}) (tx *DB) {
	tx = db.Limit(1).Order(clause.OrderByColumn{
		Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey},
		Desc:   true,
	})
	if len(conds) > 0 {
		if exprs := tx.Statement.BuildCondition(conds[0], conds[1:]...); len(exprs) > 0 {
			tx.Statement.AddClause(clause.Where{Exprs: exprs})
		}
	}
	tx.Statement.RaiseErrorOnNotFound = true
	tx.Statement.Dest = dest
	return tx.callbacks.Query().Execute(tx)
}

4.10Find方法

// Find find records that match given conditions
func (db *DB) Find(dest interface{}, conds ...interface{}) (tx *DB) {
	tx = db.getInstance()
	if len(conds) > 0 {
		if exprs := tx.Statement.BuildCondition(conds[0], conds[1:]...); len(exprs) > 0 {
			tx.Statement.AddClause(clause.Where{Exprs: exprs})
		}
	}
	tx.Statement.Dest = dest
	return tx.callbacks.Query().Execute(tx)
}

4.11FindInBatches方法

// FindInBatches find records in batches
func (db *DB) FindInBatches(dest interface{}, batchSize int, fc func(tx *DB, batch int) error) *DB {
	var (
		tx = db.Order(clause.OrderByColumn{
			Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey},
		}).Session(&Session{})
		queryDB      = tx
		rowsAffected int64
		batch        int
	)

	for {
		result := queryDB.Limit(batchSize).Find(dest)
		rowsAffected  = result.RowsAffected
		batch  

		if result.Error == nil && result.RowsAffected != 0 {
			tx.AddError(fc(result, batch))
		} else if result.Error != nil {
			tx.AddError(result.Error)
		}

		if tx.Error != nil || int(result.RowsAffected) < batchSize {
			break
		}

		// Optimize for-break
		resultsValue := reflect.Indirect(reflect.ValueOf(dest))
		if result.Statement.Schema.PrioritizedPrimaryField == nil {
			tx.AddError(ErrPrimaryKeyRequired)
			break
		}

		primaryValue, _ := result.Statement.Schema.PrioritizedPrimaryField.ValueOf(tx.Statement.Context, resultsValue.Index(resultsValue.Len()-1))
		queryDB = tx.Clauses(clause.Gt{Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey}, Value: primaryValue})
	}

	tx.RowsAffected = rowsAffected
	return tx
}

4.12assignInterfacesToValue方法

func (db *DB) assignInterfacesToValue(values ...interface{}) {
	for _, value := range values {
		switch v := value.(type) {
		case []clause.Expression:
			for _, expr := range v {
				if eq, ok := expr.(clause.Eq); ok {
					switch column := eq.Column.(type) {
					case string:
						if field := db.Statement.Schema.LookUpField(column); field != nil {
							db.AddError(field.Set(db.Statement.Context, db.Statement.ReflectValue, eq.Value))
						}
					case clause.Column:
						if field := db.Statement.Schema.LookUpField(column.Name); field != nil {
							db.AddError(field.Set(db.Statement.Context, db.Statement.ReflectValue, eq.Value))
						}
					}
				} else if andCond, ok := expr.(clause.AndConditions); ok {
					db.assignInterfacesToValue(andCond.Exprs)
				}
			}
		case clause.Expression, map[string]string, map[interface{}]interface{}, map[string]interface{}:
			if exprs := db.Statement.BuildCondition(value); len(exprs) > 0 {
				db.assignInterfacesToValue(exprs)
			}
		default:
			if s, err := schema.Parse(value, db.cacheStore, db.NamingStrategy); err == nil {
				reflectValue := reflect.Indirect(reflect.ValueOf(value))
				switch reflectValue.Kind() {
				case reflect.Struct:
					for _, f := range s.Fields {
						if f.Readable {
							if v, isZero := f.ValueOf(db.Statement.Context, reflectValue); !isZero {
								if field := db.Statement.Schema.LookUpField(f.Name); field != nil {
									db.AddError(field.Set(db.Statement.Context, db.Statement.ReflectValue, v))
								}
							}
						}
					}
				}
			} else if len(values) > 0 {
				if exprs := db.Statement.BuildCondition(values[0], values[1:]...); len(exprs) > 0 {
					db.assignInterfacesToValue(exprs)
				}
				return
			}
		}
	}
}

4.13FirstOrInit方法

// FirstOrInit gets the first matched record or initialize a new instance with given conditions (only works with struct or map conditions)
func (db *DB) FirstOrInit(dest interface{}, conds ...interface{}) (tx *DB) {
	queryTx := db.Limit(1).Order(clause.OrderByColumn{
		Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey},
	})

	if tx = queryTx.Find(dest, conds...); queryTx.RowsAffected == 0 {
		if c, ok := tx.Statement.Clauses["WHERE"]; ok {
			if where, ok := c.Expression.(clause.Where); ok {
				tx.assignInterfacesToValue(where.Exprs)
			}
		}

		// initialize with attrs, conds
		if len(tx.Statement.attrs) > 0 {
			tx.assignInterfacesToValue(tx.Statement.attrs...)
		}
	}

	// initialize with attrs, conds
	if len(tx.Statement.assigns) > 0 {
		tx.assignInterfacesToValue(tx.Statement.assigns...)
	}
	return
}

4.14FirstOrCreate方法

// FirstOrCreate gets the first matched record or create a new one with given conditions (only works with struct, map conditions)
func (db *DB) FirstOrCreate(dest interface{}, conds ...interface{}) (tx *DB) {
	queryTx := db.Limit(1).Order(clause.OrderByColumn{
		Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey},
	})
	if tx = queryTx.Find(dest, conds...); tx.Error == nil {
		if tx.RowsAffected == 0 {
			if c, ok := tx.Statement.Clauses["WHERE"]; ok {
				if where, ok := c.Expression.(clause.Where); ok {
					tx.assignInterfacesToValue(where.Exprs)
				}
			}

			// initialize with attrs, conds
			if len(tx.Statement.attrs) > 0 {
				tx.assignInterfacesToValue(tx.Statement.attrs...)
			}

			// initialize with attrs, conds
			if len(tx.Statement.assigns) > 0 {
				tx.assignInterfacesToValue(tx.Statement.assigns...)
			}

			return tx.Create(dest)
		} else if len(db.Statement.assigns) > 0 {
			exprs := tx.Statement.BuildCondition(db.Statement.assigns[0], db.Statement.assigns[1:]...)
			assigns := map[string]interface{}{}
			for _, expr := range exprs {
				if eq, ok := expr.(clause.Eq); ok {
					switch column := eq.Column.(type) {
					case string:
						assigns[column] = eq.Value
					case clause.Column:
						assigns[column.Name] = eq.Value
					default:
					}
				}
			}

			return tx.Model(dest).Updates(assigns)
		}
	}
	return tx
}

4.15Update方法

// Update update attributes with callbacks, refer: https://gorm.io/docs/update.html#Update-Changed-Fields
func (db *DB) Update(column string, value interface{}) (tx *DB) {
	tx = db.getInstance()
	tx.Statement.Dest = map[string]interface{}{column: value}
	return tx.callbacks.Update().Execute(tx)
}

4.16Updates方法

// Updates update attributes with callbacks, refer: https://gorm.io/docs/update.html#Update-Changed-Fields
func (db *DB) Updates(values interface{}) (tx *DB) {
	tx = db.getInstance()
	tx.Statement.Dest = values
	return tx.callbacks.Update().Execute(tx)
}

4.17UpdateColumn方法

func (db *DB) UpdateColumn(column string, value interface{}) (tx *DB) {
	tx = db.getInstance()
	tx.Statement.Dest = map[string]interface{}{column: value}
	tx.Statement.SkipHooks = true
	return tx.callbacks.Update().Execute(tx)
}

4.18UpdateColumns方法

func (db *DB) UpdateColumns(values interface{}) (tx *DB) {
	tx = db.getInstance()
	tx.Statement.Dest = values
	tx.Statement.SkipHooks = true
	return tx.callbacks.Update().Execute(tx)
}

4.19Delete方法

// Delete delete value match given conditions, if the value has primary key, then will including the primary key as condition
func (db *DB) Delete(value interface{}, conds ...interface{}) (tx *DB) {
	tx = db.getInstance()
	if len(conds) > 0 {
		if exprs := tx.Statement.BuildCondition(conds[0], conds[1:]...); len(exprs) > 0 {
			tx.Statement.AddClause(clause.Where{Exprs: exprs})
		}
	}
	tx.Statement.Dest = value
	return tx.callbacks.Delete().Execute(tx)
}

4.20Count方法

func (db *DB) Count(count *int64) (tx *DB) {

4.21Row()方法

func (db *DB) Row() *sql.Row {
	tx := db.getInstance().Set("rows", false)
	tx = tx.callbacks.Row().Execute(tx)
	row, ok := tx.Statement.Dest.(*sql.Row)
	if !ok && tx.DryRun {
		db.Logger.Error(tx.Statement.Context, ErrDryRunModeUnsupported.Error())
	}
	return row
}

4.22Rows()方法

func (db *DB) Rows() (*sql.Rows, error) {
	tx := db.getInstance().Set("rows", true)
	tx = tx.callbacks.Row().Execute(tx)
	rows, ok := tx.Statement.Dest.(*sql.Rows)
	if !ok && tx.DryRun && tx.Error == nil {
		tx.Error = ErrDryRunModeUnsupported
	}
	return rows, tx.Error
}

4.23Scan方法

// Scan scan value to a struct
func (db *DB) Scan(dest interface{}) (tx *DB) {
	config := *db.Config
	currentLogger, newLogger := config.Logger, logger.Recorder.New()
	config.Logger = newLogger

	tx = db.getInstance()
	tx.Config = &config

	if rows, err := tx.Rows(); err == nil {
		if rows.Next() {
			tx.ScanRows(rows, dest)
		} else {
			tx.RowsAffected = 0
		}
		tx.AddError(rows.Close())
	}

	currentLogger.Trace(tx.Statement.Context, newLogger.BeginAt, func() (string, int64) {
		return newLogger.SQL, tx.RowsAffected
	}, tx.Error)
	tx.Logger = currentLogger
	return
}

4.24Pluck方法

// Pluck used to query single column from a model as a map
//     var ages []int64
//     db.Model(&users).Pluck("age", &ages)
func (db *DB) Pluck(column string, dest interface{}) (tx *DB) {
	tx = db.getInstance()
	if tx.Statement.Model != nil {
		if tx.Statement.Parse(tx.Statement.Model) == nil {
			if f := tx.Statement.Schema.LookUpField(column); f != nil {
				column = f.DBName
			}
		}
	}

	if len(tx.Statement.Selects) != 1 {
		fields := strings.FieldsFunc(column, utils.IsValidDBNameChar)
		tx.Statement.AddClauseIfNotExists(clause.Select{
			Distinct: tx.Statement.Distinct,
			Columns:  []clause.Column{{Name: column, Raw: len(fields) != 1}},
		})
	}
	tx.Statement.Dest = dest
	return tx.callbacks.Query().Execute(tx)
}

4.25ScanRows方法

func (db *DB) ScanRows(rows *sql.Rows, dest interface{}) error {
	tx := db.getInstance()
	if err := tx.Statement.Parse(dest); !errors.Is(err, schema.ErrUnsupportedDataType) {
		tx.AddError(err)
	}
	tx.Statement.Dest = dest
	tx.Statement.ReflectValue = reflect.ValueOf(dest)
	for tx.Statement.ReflectValue.Kind() == reflect.Ptr {
		elem := tx.Statement.ReflectValue.Elem()
		if !elem.IsValid() {
			elem = reflect.New(tx.Statement.ReflectValue.Type().Elem())
			tx.Statement.ReflectValue.Set(elem)
		}
		tx.Statement.ReflectValue = elem
	}
	Scan(rows, tx, ScanInitialized)
	return tx.Error
}

4.26Connection方法

// Connection  use a db conn to execute Multiple commands,this conn will put conn pool after it is executed.
func (db *DB) Connection(fc func(tx *DB) error) (err error) {
	if db.Error != nil {
		return db.Error
	}

	tx := db.getInstance()
	sqlDB, err := tx.DB()
	if err != nil {
		return
	}

	conn, err := sqlDB.Conn(tx.Statement.Context)
	if err != nil {
		return
	}

	defer conn.Close()
	tx.Statement.ConnPool = conn
	return fc(tx)
}

4.27Transaction方法

// Transaction start a transaction as a block, return error will rollback, otherwise to commit.
func (db *DB) Transaction(fc func(tx *DB) error, opts ...*sql.TxOptions) (err error) {}

4.28Begin方法

// Begin begins a transaction
func (db *DB) Begin(opts ...*sql.TxOptions) *DB {}

4.29Commit方法

// Commit commit a transaction
func (db *DB) Commit() *DB {
	if committer, ok := db.Statement.ConnPool.(TxCommitter); ok && committer != nil && !reflect.ValueOf(committer).IsNil() {
		db.AddError(committer.Commit())
	} else {
		db.AddError(ErrInvalidTransaction)
	}
	return db
}

4.30Rollback方法

// Rollback rollback a transaction
func (db *DB) Rollback() *DB {}

4.31SavePoint方法

func (db *DB) SavePoint(name string) *DB {}

4.32RollbackTo方法

func (db *DB) RollbackTo(name string) *DB {}

4.33Exec方法

// Exec execute raw sql
func (db *DB) Exec(sql string, values ...interface{}) (tx *DB) {}

5.gorm.Option接口

// Option gorm option interface
type Option interface {
	Apply(*Config) error
	AfterInitialize(*DB) error
}

6.gorm.Migrator接口

// Migrator migrator interface
type Migrator interface {
	// AutoMigrate
	AutoMigrate(dst ...interface{}) error

	// Database
	CurrentDatabase() string
	FullDataTypeOf(*schema.Field) clause.Expr

	// Tables
	CreateTable(dst ...interface{}) error
	DropTable(dst ...interface{}) error
	HasTable(dst interface{}) bool
	RenameTable(oldName, newName interface{}) error
	GetTables() (tableList []string, err error)

	// Columns
	AddColumn(dst interface{}, field string) error
	DropColumn(dst interface{}, field string) error
	AlterColumn(dst interface{}, field string) error
	MigrateColumn(dst interface{}, field *schema.Field, columnType ColumnType) error
	HasColumn(dst interface{}, field string) bool
	RenameColumn(dst interface{}, oldName, field string) error
	ColumnTypes(dst interface{}) ([]ColumnType, error)

	// Views
	CreateView(name string, option ViewOption) error
	DropView(name string) error

	// Constraints
	CreateConstraint(dst interface{}, name string) error
	DropConstraint(dst interface{}, name string) error
	HasConstraint(dst interface{}, name string) bool

	// Indexes
	CreateIndex(dst interface{}, name string) error
	DropIndex(dst interface{}, name string) error
	HasIndex(dst interface{}, name string) bool
	RenameIndex(dst interface{}, oldName, newName string) error
}

7.ColumnType接口

// ColumnType column type interface
type ColumnType interface {
	Name() string
	DatabaseTypeName() string                 // varchar
	ColumnType() (columnType string, ok bool) // varchar(64)
	PrimaryKey() (isPrimaryKey bool, ok bool)
	AutoIncrement() (isAutoIncrement bool, ok bool)
	Length() (length int64, ok bool)
	DecimalSize() (precision int64, scale int64, ok bool)
	Nullable() (nullable bool, ok bool)
	Unique() (unique bool, ok bool)
	ScanType() reflect.Type
	Comment() (value string, ok bool)
	DefaultValue() (value string, ok bool)
}

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