func (r *Runner) invokeMigration(isTest bool, m Migration, c *spiffy.DbConnection, optionalTx ...*sql.Tx) (err error) {
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("%v", err)
		}
	}()

	if m.IsTransactionIsolated() {
		err = m.Apply(c, spiffy.OptionalTx(optionalTx...))
		return
	}

	var tx *sql.Tx
	tx, err = c.Begin()
	if err != nil {
		return err
	}
	defer func() {
		if err == nil {
			err = exception.Wrap(tx.Commit())
		} else {
			err = exception.WrapMany(err, exception.New(tx.Rollback()))
		}
	}()
	err = m.Apply(c, tx)
	return
}

// Invoke executes the statement block
func (s Statement) Invoke(c *spiffy.DbConnection, tx *sql.Tx) (err error) {
	for _, step := range s {
		err = c.ExecInTx(step, tx)
		if err != nil {
			return
		}
	}
	return
}

// Test runs the data file reader and then rolls-back the txn.
func (dfr *DataFileReader) Test(c *spiffy.DbConnection, optionalTx ...*sql.Tx) (err error) {
	tx, err := c.Begin()
	if err != nil {
		return
	}
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("%v", err)
		}
		if err == nil {
			dfr.logger.Applyf(dfr, "done!")
		} else {
			dfr.logger.Errorf(dfr, err)
		}
		tx.Rollback()
	}()
	err = dfr.invoke(c, tx)
	return
}

// Invoke consumes the data file and writes it to the db.
func (dfr *DataFileReader) invoke(c *spiffy.DbConnection, tx *sql.Tx) (err error) {
	var f *os.File
	if f, err = os.Open(dfr.path); err != nil {
		return
	}
	defer f.Close()

	var stmt *sql.Stmt
	var state int

	var cursor int64
	var readBuffer = make([]byte, 32)
	var readErr error
	var lineBuffer = bytes.NewBuffer([]byte{})
	var line string
	var pieces []interface{}

	for readErr == nil {
		lineBuffer.Reset()

		switch state {
		case 0:
			cursor, readErr = dfr.readLine(f, cursor, readBuffer, lineBuffer)
			if readErr != nil {
				continue
			}
			line = lineBuffer.String()

			if spiffy.HasPrefixCaseInsensitive(line, "--") {
				continue
			}

			if spiffy.HasPrefixCaseInsensitive(line, "set") {
				continue
			}

			if spiffy.HasPrefixCaseInsensitive(line, "copy") {
				if !spiffy.HasSuffixCaseInsensitive(line, "from stdin;") {
					err = fmt.Errorf("Only `stdin` from clauses supported at this time, cannot continue.")
					return
				}

				stmt, err = dfr.executeCopyLine(line, c, tx)
				if err != nil {
					return
				}
				state = 1
				continue
			}

			err = c.ExecInTx(line, tx)
			if err != nil {
				return
			}
		case 1:
			pieces, cursor, readErr = dfr.readTabLine(f, cursor, readBuffer, lineBuffer)
			if readErr != nil {
				continue
			}

			if len(pieces) == 0 {
				err = fmt.Errorf("Empty data line, we error on this for now.")
				return
			}

			if len(pieces) == 1 && spiffy.HasPrefixCaseInsensitive(pieces[0].(string), `\.`) {
				err = stmt.Close()
				if err != nil {
					return
				}
				state = 0
				continue
			}

			_, err = stmt.Exec(pieces...)
			if err != nil {
				return
			}
		}
	}
	return nil
}

func spiffyAccess(db *spiffy.DbConnection, queryLimit int) ([]testObject, error) {
	var results []testObject
	err := db.GetAll(&results)
	return results, err
}

// roleExists returns if a role exists or not.
func roleExists(c *spiffy.DbConnection, tx *sql.Tx, roleName string) (bool, error) {
	return c.QueryInTx(`SELECT 1 FROM pg_roles WHERE rolname ilike $1`, tx, roleName).Any()
}

// IndexExists returns if a index exists on a table on the given connection.
func indexExists(c *spiffy.DbConnection, tx *sql.Tx, tableName, indexName string) (bool, error) {
	return c.QueryInTx(`SELECT 1 FROM pg_catalog.pg_index ix join pg_catalog.pg_class t on t.oid = ix.indrelid join pg_catalog.pg_class i on i.oid = ix.indexrelid WHERE t.relname = $1 and i.relname = $2 and t.relkind = 'r'`, tx, strings.ToLower(tableName), strings.ToLower(indexName)).Any()
}

// ConstraintExists returns if a constraint exists on a table on the given connection.
func constraintExists(c *spiffy.DbConnection, tx *sql.Tx, constraintName string) (bool, error) {
	return c.QueryInTx(`SELECT 1 FROM pg_constraint WHERE conname = $1`, tx, strings.ToLower(constraintName)).Any()
}

// ColumnExists returns if a column exists on a table on the given connection.
func columnExists(c *spiffy.DbConnection, tx *sql.Tx, tableName, columnName string) (bool, error) {
	return c.QueryInTx(`SELECT 1 FROM information_schema.columns i WHERE i.table_name = $1 and i.column_name = $2`, tx, strings.ToLower(tableName), strings.ToLower(columnName)).Any()
}

// TableExists returns if a table exists on the given connection.
func tableExists(c *spiffy.DbConnection, tx *sql.Tx, tableName string) (bool, error) {
	return c.QueryInTx(`SELECT 1 FROM pg_catalog.pg_tables WHERE tablename = $1`, tx, strings.ToLower(tableName)).Any()
}