mermaid-js/mermaid · error

The group id [${id}] is already in use by another ${this.reg

Error message

The group id [${id}] is already in use by another ${this.registeredIds.get(id)}

What it means

Thrown by addGroup when the group id already exists in registeredIds. Groups share the id namespace with services and junctions, so a collision with any prior entity trips this; the suffix ('node' or 'group') indicates the prior owner type.

Source

Thrown at packages/mermaid/src/diagrams/architecture/architectureDb.ts:162

      in: parent,
    });
  }

  public getJunctions(): ArchitectureJunction[] {
    return [...this.nodes.values()].filter(isArchitectureJunction);
  }

  public getNodes(): ArchitectureNode[] {
    return [...this.nodes.values()];
  }

  public getNode(id: string): ArchitectureNode | null {
    return this.nodes.get(id) ?? null;
  }

  public addGroup({ id, icon, in: parent, title }: ArchitectureGroup): void {
    if (this.registeredIds.has(id)) {
      throw new Error(
        `The group id [${id}] is already in use by another ${this.registeredIds.get(id)}`
      );
    }
    if (parent !== undefined) {
      if (id === parent) {
        throw new Error(`The group [${id}] cannot be placed within itself`);
      }
      if (!this.registeredIds.has(parent)) {
        throw new Error(
          `The group [${id}]'s parent does not exist. Please make sure the parent is created before this group`
        );
      }
      if (this.registeredIds.get(parent) === 'node') {
        throw new Error(`The group [${id}]'s parent is not a group`);
      }
    }

    this.registeredIds.set(id, 'group');

View on GitHub (pinned to d93e9c88c0)

Solutions

1. Give each group a unique id; namespace if labels repeat.
2. Check db.getGroups()/registeredIds before adding.
3. If a clash is intentional, rename one entity and keep the title for display.

Example fix

// before
db.addGroup({ id: 'net' });
db.addGroup({ id: 'net' }); // throws

// after
db.addGroup({ id: 'net1', title: 'net' });
db.addGroup({ id: 'net2', title: 'net' });

if (db.getGroups().some((g) => g.id === id) || db.getNode(id) !== null) {
  throw new Error(`id '${id}' already in use`);
}
db.addGroup({ id });

function isGroupIdFree(db: ArchitectureDB, id: string): boolean {
  return db.getNode(id) === null && !db.getGroups().some((g) => g.id === id);
}

When it happens

Trigger: addGroup with an id already used by another group, a service, or a junction; defining two groups with the same id.

Common situations: Duplicate group labels in user text, generated specs with non-unique group ids, or a group id reused as a service id.

Related errors

• The service id [${id}] is already in use by another ${this.r
• The service [${id}]'s parent is not a group
• The junction id [${id}] is already in use by another ${this.
• The junction [${id}]'s parent is not a group
• The service [${id}] cannot be placed within itself

AI-assisted analysis of mermaid-js/mermaid@d93e9c88c0 (2026-08-12). Data as JSON: /api/errors/d1fa370d31ac4b08. Report an issue: GitHub.