Method dumpTableConstraints

dgraph/cmd/migrate/dump.go:136–167

dumpTableConstraints reads data from a table, and then generate RDF entries from a row to another row in a foreign table by following columns with foreign key constraints. It then sends the generated RDF entries to the m.dataWriter

(table string)

// from a row to another row in a foreign table by following columns with foreign key constraints.
// It then sends the generated RDF entries to the m.dataWriter
func (m *dumpMeta) dumpTableConstraints(table string) error {
	tableGuide := m.tableGuides[table]
	tableInfo := m.tableInfos[table]

	escapedColNames := escapeColumnNames(tableInfo.columnNames)

	query := fmt.Sprintf(`select %s from %s`, strings.Join(escapedColNames, ","), table)
	rows, err := m.sqlPool.Query(query)
	if err != nil {
		return err
	}
	defer rows.Close()

	row := &sqlRow{
		tableInfo: tableInfo,
	}
	for rows.Next() {
		// step 1: read the row's column values
		colValues, err := getColumnValues(tableInfo.columnNames, tableInfo.columnDataTypes, rows)
		if err != nil {
			return err
		}
		row.values = colValues

		// step 2: output the constraints in RDF format
		row.blankNodeLabel = tableGuide.blankNode.generate(tableInfo, colValues)

		m.outputConstraints(row, tableInfo)
	}

	return nil
}

// outputRow takes a row with its metadata as well as the table metadata, and
// spits out one or more RDF entries to the dumpMeta's dataWriter.