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Version: 5.0


Describe a schema which is a union of multiple schemas. This is useful if you need the polymorphic behavior provided by schema.Array or schema.Values but for non-collection fields.

  • definition: required An object mapping the definition of the nested entities found within the input array
  • schemaAttribute: required The attribute on each entity found that defines what schema, per the definition mapping, to use when normalizing. Can be a string or a function. If given a function, accepts the following arguments:
    • value: The input value of the entity.
    • parent: The parent object of the input array.
    • key: The key at which the input array appears on the parent object.

Instance Methods

  • define(definition): When used, the definition passed in will be merged with the original definition passed to the Union constructor. This method tends to be useful for creating circular references in schema.


Note: If your data returns an object that you did not provide a mapping for, the original object will be returned in the result and an entity will not be created.

const data = { owner: { id: 1, type: 'user', name: 'Anne' } };

class User extends Entity {
readonly id: number = 0;
readonly type = 'user' as const;
readonly name: string = '';
pk() { return `${}`; }
class Group extends Entity {
readonly id: number = 0;
readonly type = 'admin' as const;
pk() { return `${}`; }
const unionSchema = new schema.Union(
user: User,
group: Group

const normalizedData = normalize(data, { owner: unionSchema });


entities: {
User: { '1': { id: 1, type: 'user', name: 'Anne' } }
result: { owner: { id: 1, schema: 'User' } }