Golang Service.Read方法代碼示例

// EnsureReverseEdges checks if gs contains reverse edges.  If it doesn't, it
// will scan gs for all forward edges, adding a reverse for each back into the
// GraphStore.  This is necessary for a GraphStoreService to work properly.
func EnsureReverseEdges(ctx context.Context, gs graphstore.Service) error {
	var edge *spb.Entry
	if err := gs.Scan(ctx, &spb.ScanRequest{}, func(e *spb.Entry) error {
		if graphstore.IsEdge(e) {
			edge = e
			return io.EOF
		}
		return nil
	}); err != nil {
		return err
	}

	if edge == nil {
		log.Println("No edges found in GraphStore")
		return nil
	} else if schema.EdgeDirection(edge.EdgeKind) == schema.Reverse {
		return nil
	}

	var foundReverse bool
	if err := gs.Read(ctx, &spb.ReadRequest{
		Source:   edge.Target,
		EdgeKind: schema.MirrorEdge(edge.EdgeKind),
	}, func(entry *spb.Entry) error {
		foundReverse = true
		return nil
	}); err != nil {
		return fmt.Errorf("error checking for reverse edge: %v", err)
	}
	if foundReverse {
		return nil
	}
	return addReverseEdges(ctx, gs)
}

func readEntries(ctx context.Context, gs graphstore.Service, entryFunc graphstore.EntryFunc, edgeKind string, tickets []string) error {
	for _, ticket := range tickets {
		src, err := kytheuri.ToVName(ticket)
		if err != nil {
			return fmt.Errorf("error parsing ticket %q: %v", ticket, err)
		}
		if err := gs.Read(ctx, &spb.ReadRequest{
			Source:   src,
			EdgeKind: edgeKind,
		}, entryFunc); err != nil {
			return fmt.Errorf("GraphStore Read error for ticket %q: %v", ticket, err)
		}
	}
	return nil
}

// getEdges returns edgeTargets with the given node as their source.  Only edge
// entries that return true when applied to pred are returned.
func getEdges(ctx context.Context, gs graphstore.Service, node *spb.VName, pred func(*spb.Entry) bool) ([]*edgeTarget, error) {
	var targets []*edgeTarget

	if err := gs.Read(ctx, &spb.ReadRequest{
		Source:   node,
		EdgeKind: "*",
	}, func(entry *spb.Entry) error {
		if graphstore.IsEdge(entry) && pred(entry) {
			targets = append(targets, &edgeTarget{entry.EdgeKind, entry.Target})
		}
		return nil
	}); err != nil {
		return nil, fmt.Errorf("read error: %v", err)
	}
	return targets, nil
}

func getSourceText(ctx context.Context, gs graphstore.Service, fileVName *spb.VName) (text []byte, encoding string, err error) {
	if err := gs.Read(ctx, &spb.ReadRequest{Source: fileVName}, func(entry *spb.Entry) error {
		switch entry.FactName {
		case schema.TextFact:
			text = entry.FactValue
		case schema.TextEncodingFact:
			encoding = string(entry.FactValue)
		default:
			// skip other file facts
		}
		return nil
	}); err != nil {
		return nil, "", fmt.Errorf("read error: %v", err)
	}
	if text == nil {
		err = fmt.Errorf("file not found: %+v", fileVName)
	}
	return
}