dbschema/upgrader.go

package dbschema

import (
	// External
	"github.com/lib/pq"

	// Standard
	"database/sql"
	"fmt"
)

func defaultCallback(topic, msg string) {// {{{
	fmt.Printf("[%s] %s\n", topic, msg)
}// }}}

// NewUpgrader creates an upgrader with an empty list of databases.
func NewUpgrader() (upgrader Upgrader) {// {{{
	upgrader.logCallback = defaultCallback
	upgrader.databases = map[string]Database{}
	return
}// }}}

// SetLogCallback allows to set a callback for custom logging.
func (upgrader *Upgrader) SetLogCallback(callback func(string, string)) {// {{{
	upgrader.logCallback = callback
}// }}}
// SetSqlCallback is required for providing the SQL schema updates.
func (upgrader *Upgrader) SetSqlCallback(callback func(string, int) ([]byte, bool)) {// {{{
	upgrader.sqlCallback = callback
}// }}}
// Version returns the current dbschema version for the given database name.
func (upgrader *Upgrader) Version(dbName string) (version int, err error) {// {{{
	dbase, found := upgrader.databases[dbName]
	if !found {
		err = fmt.Errorf("Database %s not previously added to the upgrader", dbName)
		return
	}

	version, err = dbase.version()
	return
}// }}}

func (dbase Database) createSchemaTable() (err error) {// {{{
	dbase.upgrader.logCallback("create", fmt.Sprintf("%s, _db.schema", dbase.DbName))
	_, err = dbase.db.Exec(`CREATE SCHEMA "_db"`)

	// Error code 42P06 "duplicate_schema" is an OK error,
	// table can still be missing and created.
	pqErr, _ := err.(*pq.Error)
	if pqErr != nil && pqErr.Code != "42P06" {
		return
	}

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

			CONSTRAINT schema_pk PRIMARY KEY (version)
		)`,
	)
	return
}// }}}
func (dbase Database) appendSchemaVersion(version int) (err error) {// {{{
	_, err = dbase.db.Exec(`INSERT INTO _db.schema(version) VALUES($1)`, version)
	return
}// }}}

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 {
		return
	}
	err = dbase.createSchemaTable()
	return
}// }}}
func (dbase Database) verifySchemaEntry() (err error) {// {{{
	var version int
	var row *sql.Row
	row = dbase.db.QueryRow(`SELECT version FROM _db.schema LIMIT 1`)

	err = row.Scan(&version)
	if err == sql.ErrNoRows {
		dbase.upgrader.logCallback("initiate version", dbase.DbName)
		err = dbase.appendSchemaVersion(0)
	}

	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
}// }}}

// AddDatabase sets a database up for the Run() function with verifying/creating the _db.schema table.
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
}// }}}
// Run executes the actual schema updates until there are no more available.
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
			}
			if err = dbase.appendSchemaVersion(version); err != nil {
				return
			}
		}
	}
	return
}// }}}

// vim: foldmethod=marker