Implementation:Datahub project Datahub TagVisitor

Knowledge Sources	Datahub_project_Datahub
Domains	Protobuf_Integration, Tag_Management
Last Updated	2026-02-10 00:00 GMT

Overview

Description

TagVisitor is a visitor that creates DataHub tag entities from protobuf extension options. It implements ProtobufModelVisitor<MetadataChangeProposalWrapper<? extends RecordTemplate>> and processes both message-level and field-level options to produce tagProperties aspect MCPs.

The visitor extracts tag properties from protobuf options using ProtobufExtensionUtil.extractTagPropertiesFromOptions and wraps each extracted TagProperties into a MetadataChangeProposalWrapper targeting the "tag" entity type with a TagUrn derived from the tag name.

This visitor creates the tag entities themselves (via tagProperties aspect), as distinct from the tag associations on datasets and fields handled by other visitors.

Usage

Typically used alongside DatasetVisitor to ensure that any tags referenced from protobuf extensions are created as first-class tag entities in DataHub.

Code Reference

Source Location

metadata-integration/java/datahub-protobuf/src/main/java/datahub/protobuf/visitors/tags/TagVisitor.java

Signature

public class TagVisitor
    implements ProtobufModelVisitor<MetadataChangeProposalWrapper<? extends RecordTemplate>> {

    @Override
    public Stream<MetadataChangeProposalWrapper<? extends RecordTemplate>> visitGraph(
        VisitContext context)

    @Override
    public Stream<MetadataChangeProposalWrapper<? extends RecordTemplate>> visitField(
        ProtobufField field, VisitContext context)
}

Import

import datahub.protobuf.visitors.tags.TagVisitor;

I/O Contract

Inputs

Method	Parameter	Type	Description
visitGraph	context	VisitContext	Visit context providing root message, graph, and registry
visitField	field	ProtobufField	The field whose options to extract tags from
visitField	context	VisitContext	Visit context providing graph and registry

Outputs

Method	Return Type	Description
visitGraph	Stream<MetadataChangeProposalWrapper<? extends RecordTemplate>>	MCPs creating tag entities from message-level options
visitField	Stream<MetadataChangeProposalWrapper<? extends RecordTemplate>>	MCPs creating tag entities from field-level options

Each MCP has:

• Entity type: "tag"
• Entity URN: TagUrn derived from tagProperties.getName()
• Change type: UPSERT
• Aspect name: "tagProperties"

Usage Examples

TagVisitor tagVisitor = new TagVisitor();

// Visit message-level tags
Stream<MetadataChangeProposalWrapper<? extends RecordTemplate>> tagMcps =
    tagVisitor.visitGraph(visitContext);

// Visit field-level tags
Stream<MetadataChangeProposalWrapper<? extends RecordTemplate>> fieldTagMcps =
    tagVisitor.visitField(protobufField, visitContext);

Related Pages

• Datahub_project_Datahub_ProtobufExtensionUtil -- Provides extractTagPropertiesFromOptions
• Datahub_project_Datahub_ProtobufDescriptorUtils -- Provides getMessageOptions and getFieldOptions
• Datahub_project_Datahub_ProtobufDatasetVisitor -- Orchestrating visitor that produces tag associations on datasets
• Datahub_project_Datahub_ProtobufExtensionFieldVisitor -- Produces tag associations on schema fields