dbschema/upgrader.go

package dbschema

import (
	// Standard
	"database/sql"
	"fmt"
)

func defaultCallback(topic, msg string) {// {{{
	fmt.Printf("[%s] %s\n", topic, msg)
}// }}}
func NewUpgrader(host string, port int, dbName, user, pass string) (upgrader Upgrader, err error) {// {{{
	upgrader.logCallback = defaultCallback
	upgrader.databases = map[string]Database{}
	return
}// }}}

func (upgrader *Upgrader) SetLogCallback(callback func(string, string)) {// {{{
	upgrader.logCallback = callback
}// }}}
func (upgrader *Upgrader) SetSqlCallback(callback func(string, int) ([]byte, bool)) {// {{{
	upgrader.sqlCallback = callback
}// }}}

func (dbase Database) verifySchemaTable() (err error) {// {{{
	var rows *sql.Rows
	if rows, err = dbase.db.Query(
		`SELECT EXISTS (
			SELECT FROM pg_catalog.pg_class c
			JOIN   pg_catalog.pg_namespace n ON n.oid = c.relnamespace
			WHERE  n.nspname = '_db'
			AND    c.relname = 'schema'
		)`,
	); err != nil {
		return
	}
	defer rows.Close()
	var exists bool
	rows.Next()
	if err = rows.Scan(&exists); err != nil {
		return
	}

	if !exists {
		dbase.upgrader.logCallback("create", fmt.Sprintf("%s, _db.schema", dbase.DbName))
		dbase.db.Exec(`CREATE SCHEMA "_db"`)

		if _, err = dbase.db.Exec(`
			CREATE TABLE "_db"."schema" (
				version  int4      NOT NULL,
				updated  timestamp NOT NULL DEFAULT NOW(),

				CONSTRAINT schema_pk PRIMARY KEY (version)
			)`,
		); err != nil {
			return
		}
	}
	return
}// }}}
func (dbase Database) verifySchemaEntry() (err error) {// {{{
	var rows *sql.Rows
	rows, err = dbase.db.Query(`SELECT version FROM _db.schema LIMIT 1`)
	if err != nil {
		return
	}
	defer rows.Close()

	if !rows.Next() {
		dbase.upgrader.logCallback("initiate version", dbase.DbName)
		_, err = dbase.db.Exec(`INSERT INTO _db.schema(version) VALUES(0)`)
		if err != nil {
			return
		}
	}

	return
}// }}}
func (dbase Database) version() (version int, err error) {// {{{
	var rows *sql.Rows
	rows, err = dbase.db.Query(
		`SELECT version FROM _db.schema ORDER BY version DESC LIMIT 1`,
	)
	if err != nil {
		return
	}
	defer rows.Close()

	if rows.Next() {
		err = rows.Scan(&version)
	} else {
		err = fmt.Errorf(`Database "%s" is missing an entry in _db.schema`, dbase.DbName)
	}
	return
}// }}}

func (upgrader Upgrader) AddDatabase(host string, port int, dbName, user, pass string) (err error) {// {{{
	var db Database
	if db, err = newDatabase(host, port, dbName, user, pass); err != nil {
		return
	}
	db.upgrader = &upgrader
	
	upgrader.databases[dbName] = db

	if err = db.verifySchemaTable(); err != nil {
		return
	}

	err = db.verifySchemaEntry()
	return
}// }}}
func (upgrader Upgrader) Run() (err error) {// {{{
	var version int

	for dbName, dbase := range upgrader.databases {
		version, err = dbase.version()
		if err != nil {
			return
		}
		upgrader.logCallback("version", fmt.Sprintf("%s: %d", dbName, version))

		for {
			version++
			sql, found := upgrader.sqlCallback(dbName, version)
			if !found {
				break
			}

			upgrader.logCallback("exec", fmt.Sprintf("%s: %d", dbName, version))
			if _, err = dbase.db.Exec(string(sql)); err != nil {
				return
			}
			_, err = dbase.db.Exec(`
				INSERT INTO _db.schema(version)
				VALUES($1)
			`, version)
			if err != nil {
				return
			}
		}
	}
	return
}// }}}

// vim: foldmethod=marker