alter.go
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alter.go
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	package db

	import (
	"fmt"
	"strings"
	)

	type AlterTableSqlBuilder struct {
	Dialect DialectType
	Name string
	Changes []string
	}

	func (b AlterTableSqlBuilder) AddColumn(col Column) *AlterTableSqlBuilder {
	if colVal, err := col.String(); err == nil {
	b.Changes = append(b.Changes, fmt.Sprintf("ADD COLUMN %s", colVal))
	}
	return b
	}

	func (b AlterTableSqlBuilder) ChangeColumn(name string, col Column) *AlterTableSqlBuilder {
	if colVal, err := col.String(); err == nil {
	b.Changes = append(b.Changes, fmt.Sprintf("CHANGE COLUMN %s %s", name, colVal))
	}
	return b
	}

	func (b AlterTableSqlBuilder) AddUniqueConstraint(name string, columns ...string) AlterTableSqlBuilder {
	b.Changes = append(b.Changes, fmt.Sprintf("ADD CONSTRAINT %s UNIQUE (%s)", name, strings.Join(columns, ", ")))
	return b
	}

	func (b *AlterTableSqlBuilder) ToSQL() (string, error) {
	var str strings.Builder

	str.WriteString("ALTER TABLE ")
	str.WriteString(b.Name)
	str.WriteString(" ")

	if len(b.Changes) == 0 {
	return "", fmt.Errorf("no changes provide for table: %s", b.Name)
	}
	changeCount := len(b.Changes)
	for i, thing := range b.Changes {
	str.WriteString(thing)
	if i < changeCount-1 {
	str.WriteString(", ")
	}
	}

	return str.String(), nil
	}