Method dumpTable

dgraph/cmd/migrate/dump.go:90–131

dumpTable converts the cells in a SQL table into RDF entries, and sends entries to the m.dataWriter

(table string)

// dumpTable converts the cells in a SQL table into RDF entries,
// and sends entries to the m.dataWriter
func (m *dumpMeta) dumpTable(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()

	// populate the predNames
	for _, column := range tableInfo.columnNames {
		tableInfo.predNames = append(tableInfo.predNames,
			predicateName(tableInfo, column))
	}

	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 column values in RDF format
		row.blankNodeLabel = tableGuide.blankNode.generate(tableInfo, colValues)
		m.outputRow(row, tableInfo)

		// step 3: record mappings to the blankNodeLabel so that future tables can look up the
		// blankNodeLabel
		tableGuide.valuesRecorder.record(tableInfo, colValues, row.blankNodeLabel)
	}

	return nil
}

// 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.