Hands-On Software Engineering with Golang

Iterating links/edges

To select the links that correspond to a particular partition and whose retrieved timestamp is older than the provided value, we will use the following query:

SELECT id, url, retrieved_at FROM links WHERE id >= $1 AND id < $2 AND retrieved_at < $3

The implementation of the Links method is shown in the following listing:

func (c *CockroachDBGraph) Links(fromID, toID uuid.UUID, accessedBefore time.Time) (graph.LinkIterator, error) {
    rows, err := c.db.Query(linksInPartitionQuery, fromID, toID, accessedBefore.UTC())
    if err != nil {
        return nil, xerrors.Errorf("links: %w", err)
    }

    return &linkIterator{rows: rows}, nil
}

As you can see, the method executes the query with the specified arguments and returns a linkIterator