Method QuerySingleAttribute

internal/storage/postgres/data_reader.go:204–260

QuerySingleAttribute retrieves a single attribute from the storage based on the given filter.

(ctx context.Context, tenantID string, filter *base.AttributeFilter, snap string)

// QuerySingleAttribute retrieves a single attribute from the storage based on the given filter.
func (r *DataReader) QuerySingleAttribute(ctx context.Context, tenantID string, filter *base.AttributeFilter, snap string) (attribute *base.Attribute, err error) {
	// Start a new trace span and end it when the function exits.
	ctx, span := internal.Tracer.Start(ctx, "data-reader.query-single-attribute")
	defer span.End()

	slog.DebugContext(ctx, "querying single attribute for tenant_id", slog.String("tenant_id", tenantID))

	// Decode the snapshot value.
	var st token.SnapToken
	st, err = snapshot.EncodedToken{Value: snap}.Decode()
	if err != nil {
		return nil, utils.HandleError(ctx, span, err, base.ErrorCode_ERROR_CODE_INTERNAL)
	}

	// Build the relationships query based on the provided filter and snapshot value.
	var args []interface{}
	builder := r.database.Builder.Select("entity_type, entity_id, attribute, value").From(AttributesTable).Where(squirrel.Eq{"tenant_id": tenantID})
	builder = utils.AttributesFilterQueryForSelectBuilder(builder, filter)
	builder = utils.SnapshotQuery(builder, st.(snapshot.Token).Value.Uint, st.(snapshot.Token).Snapshot)

	// Generate the SQL query and arguments.
	var query string
	query, args, err = builder.ToSql()
	if err != nil {
		return nil, utils.HandleError(ctx, span, err, base.ErrorCode_ERROR_CODE_SQL_BUILDER)
	}

	slog.DebugContext(ctx, "generated sql query", slog.String("query", query), "with args", slog.Any("arguments", args))
	// Execute query
	row := r.database.ReadPool.QueryRow(ctx, query, args...)

	rt := storage.Attribute{}

	// Suppose you have a struct `rt` with a field `Value` of type `*anypb.Any`.
	var valueStr string

	// Scan the row from the database into the fields of `rt` and `valueStr`.
	err = row.Scan(&rt.EntityType, &rt.EntityID, &rt.Attribute, &valueStr)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, nil
		} else {
			return nil, utils.HandleError(ctx, span, err, base.ErrorCode_ERROR_CODE_SCAN)
		}
	}

	// Unmarshal the JSON data from `valueStr` into `rt.Value`.
	rt.Value = &anypb.Any{}
	err = protojson.Unmarshal([]byte(valueStr), rt.Value)
	if err != nil {
		return nil, utils.HandleError(ctx, span, err, base.ErrorCode_ERROR_CODE_INTERNAL)
	}

	slog.DebugContext(ctx, "successfully retrieved Single attribute from the database")
	// Return attribute
	return rt.ToAttribute(), nil
}