dgraph-io/dgraph · error

expected only one unique typename in `_representations` argu

Error message

expected only one unique typename in `_representations` argument, got: [%s, %s]

What it means

Federation requires all representations in one `_entities` call to belong to the same entity type (this implementation enforces a single unique typename). This error fires when the `__typename` of the item at index i differs from the typename established for the batch, reporting both names.

Source

Thrown at graphql/schema/wrappers.go:1762

		KeyVals:                make([]interface{}, 0, len(representations)),
		KeyValToRepresentation: make(map[string]map[string]interface{}),
	}
	entityReprs.KeyField = entityReprs.TypeDefn.Field(keyFldName)

	// iterate over all the representations and parse
	for i, rep := range representations {
		representation, ok = rep.(map[string]interface{})
		if !ok {
			return nil, fmt.Errorf("error parsing %dth item in the `_representations` argument", i)
		}

		typename, ok = representation[Typename].(string)
		if !ok {
			return nil, fmt.Errorf("unable to extract __typename from %dth item in the"+
				" `_representations` argument", i)
		}
		if typename != entityReprs.TypeDefn.Name() {
			return nil, fmt.Errorf("expected only one unique typename in `_representations`"+
				" argument, got: [%s, %s]", entityReprs.TypeDefn.Name(), typename)
		}

		keyVal, ok := representation[keyFldName]
		if !ok {
			return nil, fmt.Errorf("unable to extract value for key field `%s` from %dth item in"+
				" the `_representations` argument", keyFldName, i)
		}
		entityReprs.KeyVals = append(entityReprs.KeyVals, keyVal)
		entityReprs.KeyValToRepresentation[fmt.Sprint(keyVal)] = representation
	}

	return entityReprs, nil
}

func (q *query) AuthFor(jwtVars map[string]interface{}) Query {
	// copy the template, so that multiple queries can run rewriting for the rule.
	return &query{

View on GitHub (pinned to 759e242be6)

Solutions

1. Split the call so each `_entities` request contains representations of only one type
2. Filter the representations array by __typename before batching
3. Check upstream code that aggregates representations to avoid cross-type mixing

Example fix

// before
[{"__typename":"Product","upc":"1"},{"__typename":"Review","id":"2"}]
// after
[{"__typename":"Product","upc":"1"}] // separate call for Review

types := map[string]bool{}
for _, rep := range representations {
  types[rep["__typename"].(string)] = true
}
if len(types) > 1 { return errors.New("_representations must contain a single typename") }

When it happens

Trigger: Passing representations of two different entity types (e.g. Product and Review) in a single `_representations` array.

Common situations: Bundling entities from multiple resolvers into one _entities call, or a gateway merging representations from different types into one batch.

Related errors

• error parsing `representations` argument
• expecting at least one item in `representations` argument
• error parsing %dth item in the `_representations` argument
• unable to extract __typename from %dth item in the `_represe
• type %s not found in the schema

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/e8865785b5886ca3. Report an issue: GitHub.