n8n-io/n8n · error · TypeORMError

Entity ${entityMetadata.name} using single-table inheritance

Error message

Entity ${entityMetadata.name} using single-table inheritance, it should also have a discriminator column. Did you forget to put discriminator column options?

What it means

Thrown by EntityMetadataValidator.validate inside the single-table-inheritance branch (inheritancePattern === 'STI' or tableType === 'entity-child') when no discriminatorColumn exists on the metadata. STI requires a discriminator column on the root entity so TypeORM can store the concrete subclass per row.

Source

Thrown at packages/@n8n/typeorm/src/metadata-builder/EntityMetadataValidator.ts:76

			const areConstraintNamesEqual = entityMetadata.primaryColumns.every(
				(columnMetadata, i, columnMetadatas) =>
					columnMetadata.primaryKeyConstraintName === columnMetadatas[0].primaryKeyConstraintName,
			);
			if (!areConstraintNamesEqual) {
				throw new TypeORMError(
					`Entity ${entityMetadata.name} has multiple primary columns with different constraint names. Constraint names should be the equal.`,
				);
			}
		}

		// validate if table is using inheritance it has a discriminator
		// also validate if discriminator values are not empty and not repeated
		if (
			entityMetadata.inheritancePattern === 'STI' ||
			entityMetadata.tableType === 'entity-child'
		) {
			if (!entityMetadata.discriminatorColumn)
				throw new TypeORMError(
					`Entity ${entityMetadata.name} using single-table inheritance, it should also have a discriminator column. Did you forget to put discriminator column options?`,
				);

			if (typeof entityMetadata.discriminatorValue === 'undefined')
				throw new TypeORMError(
					`Entity ${entityMetadata.name} has an undefined discriminator value. Discriminator value should be defined.`,
				);

			const sameDiscriminatorValueEntityMetadata = allEntityMetadatas.find((metadata) => {
				return (
					metadata !== entityMetadata &&
					(metadata.inheritancePattern === 'STI' || metadata.tableType === 'entity-child') &&
					metadata.tableName === entityMetadata.tableName &&
					metadata.discriminatorValue === entityMetadata.discriminatorValue &&
					metadata.inheritanceTree.some(
						(parent) => entityMetadata.inheritanceTree.indexOf(parent) !== -1,
					)
				);

View on GitHub (pinned to 5ac6606e81)

Solutions

Add @DiscriminatorColumn({ name: 'type', type: 'string' }) to the root abstract/base entity of the hierarchy.
Confirm inheritancePattern resolves to STI (TypeORM infers it from extend patterns); if you did not intend STI, remove the @ChildEntity decorator or the extends chain.
Re-run schema sync after the change so the discriminator column is materialized in the DB.

Example fix

// before
@Entity()
export abstract class Content {
  @PrimaryGeneratedColumn() id: number;
}
@Entity()
export class Article extends Content {}

// after
@Entity()
@DiscriminatorColumn({ name: 'kind', type: 'string' })
export abstract class Content {
  @PrimaryGeneratedColumn() id: number;
}
@ChildEntity()
export class Article extends Content {}

Defensive patterns

Strategy: validation

Validate before calling

function assertStiHasDiscriminator(dataSource: DataSource): string[] {
  const problems: string[] = [];
  for (const meta of dataSource.entityMetadatas) {
    const isSti = meta.inheritancePattern === 'STI' || meta.tableType === 'entity-child';
    if (isSti && !meta.discriminatorColumn) {
      problems.push(`${meta.targetName} uses STI but has no discriminator column`);
    }
  }
  return problems;
}

Try / catch

try {
  await dataSource.initialize();
} catch (err) {
  if (err.message.includes('single-table inheritance') && err.message.includes('discriminator column')) {
    // add @DiscriminatorColumn on the root entity
  }
  throw err;
}

Prevention

Treat STI hierarchies as a single unit: root must carry @DiscriminatorColumn before any @ChildEntity is added.
Add an integration test that boots the DataSource for every STI tree in the app.
Document the STI root prominently so contributors do not add children to a non-STI base.

When it happens

Trigger: Using @SingleEntityInheritance / extending an @Entity class (or marking @ChildEntity) without declaring @DiscriminatorColumn on the root entity, or declaring it on the child instead of the root.

Common situations: Adding a child entity to an STI hierarchy whose parent lacks a discriminator; refactoring an entity into STI and forgetting the discriminator decorator.

Related errors

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/2bac1cf20c3a246b. Report an issue: GitHub.