link.ts

import { EntityBase, EntityIdentifiable, Constructable } from '../entity';
import type { Expandable } from '../expandable';
import type { Selectable } from './selectable';

/**
 * Represents a navigation property of an OData entity.
 *
 * OData is a relational data model, i.e. entities can be related to one another.
 * For example, BusinessPartner is in a 1:n relation with BusinessPartnerAddress and in a 1:1 relation with Customer.
 * Like normal properties, navigation properties can be used for selecting (expanding) and filtering.
 * For example, when constructing a query on the BusinessPartner entity, an instance of `Link<BusinessPartner, Customer>`
 * can be passed as argument to the select function, e.g. `BusinessPartner.TO_CUSTOMER`.
 *
 * NOTE: Due to historical development the Link and its extensions are used in the following way:
 * OData v2 entity: 1:N -> [[Link]], 1:0..1 -> [[OneToOneLink]]
 * OData v4 entity: 1:N -> [[OneToManyLink]], 1:0..1 -> [[OneToOneLink]]
 *
 * See also: [[Selectable]]
 *
 * @typeparam EntityT - Type of the entity to be linked from
 * @typeparam LinkedEntityT - Type of the entity to be linked to
 */
export class Link<
  EntityT extends EntityBase,
  LinkedEntityT extends EntityBase = any
> implements EntityIdentifiable<EntityT> {
  /**
   * @deprecated Since v1.21.0. Use [[clone]] instead.
   * Create a new link based on a given link.
   *
   * @typeparam EntityT - Type of the entity to be linked from
   * @typeparam LinkedEntityT - Type of the entity to be linked to
   * @param link - Link to be cloned
   * @returns Newly created link
   */
  static clone<EntityT1 extends EntityBase, LinkedEntityT1 extends EntityBase>(
    link: Link<EntityT1, LinkedEntityT1>
  ): Link<EntityT1, LinkedEntityT1> {
    const clonedLink = new Link<EntityT1, LinkedEntityT1>(
      link._fieldName,
      link._entityConstructor,
      link._linkedEntity
    );
    clonedLink._selects = link._selects;
    return clonedLink;
  }

  readonly _entity: EntityT;

  /**
   * @deprecated Since v1.21.0. Use [[_selects]] directly.
   * List of selectables on the linked entity.
   */
  get selects() {
    return this._selects;
  }

  /**
   * List of selectables on the linked entity.
   */
  _selects: Selectable<LinkedEntityT>[] = [];
  _expand: Expandable<LinkedEntityT>[] = [];

  /**
   * Creates an instance of Link.
   *
   * @param _fieldName - Name of the linking field to be used in the OData request.
   * @param _entityConstructor - Constructor type of the entity the field belongs to
   * @param _linkedEntity - Constructor type of the linked entity
   */
  constructor(
    readonly _fieldName: string,
    readonly _entityConstructor: Constructable<EntityT>,
    readonly _linkedEntity: Constructable<LinkedEntityT>
  ) {}

  /**
   * Creates a selection on a linked entity. Has the same behavior as [[GetAllRequestBuilderV2.select]] and [[GetByKeyRequestBuilderV4.select]] but for linked entities.
   *
   * See also, [[Selectable]]
   *
   * @param selects - Selection of fields or links on a linked entity
   * @returns The link itself, to facilitate method chaining
   */
  select(...selects: Selectable<LinkedEntityT>[]): this {
    const link = this.clone();
    link._selects = selects;
    return link;
  }

  expand(...expands: Expandable<LinkedEntityT>[]): this {
    const link = this.clone();
    link._expand = expands;
    return link;
  }

  /**
   * Create a new link based on a given link.
   *
   * @typeparam EntityT - Type of the entity to be linked from
   * @typeparam LinkedEntityT - Type of the entity to be linked to
   * @param link - Link to be cloned
   * @returns Newly created link
   */
  clone(): this {
    const clonedLink = new (this.constructor as any)(
      this._fieldName,
      this._entityConstructor,
      this._linkedEntity
    );
    clonedLink._selects = this._selects;
    clonedLink._expand = this._expand;
    return clonedLink;
  }
}