strapi/packages/plugins/graphql/server/services/builders/resolvers/association.js

'use strict';

module.exports = ({ strapi }) => {
  const { isMorphRelation, isMedia } = strapi.plugin('graphql').service('utils').attributes;
  const { transformArgs } = strapi.plugin('graphql').service('builders').utils;

  return {
    buildAssociationResolver: ({ contentTypeUID, attributeName }) => {
      const contentType = strapi.getModel(contentTypeUID);
      const attribute = contentType.attributes[attributeName];

      if (!attribute) {
        throw new Error(
          `Failed to build an association resolver for ${contentTypeUID}::${attributeName}`
        );
      }

      const isMediaAttribute = isMedia(attribute);
      const isMorphAttribute = isMorphRelation(attribute);

      const targetUID = isMediaAttribute ? 'plugins::upload.file' : attribute.target;
      const isToMany = isMediaAttribute ? attribute.multiple : attribute.relation.endsWith('Many');

      const targetContentType = strapi.getModel(targetUID);

      return async (parent, args = {}) => {
        const transformedArgs = transformArgs(args, {
          contentType: targetContentType,
          usePagination: true,
        });

        const data = await strapi.entityService.load(
          contentTypeUID,
          parent,
          attributeName,
          transformedArgs
        );

        // If this a polymorphic association, it returns the raw data
        if (isMorphAttribute) {
          return data;
        }

        // If this is a to-many relation, it returns an object that
        // matches what the entity-response-collection's resolvers expect
        else if (isToMany) {
          return { nodes: data, info: { args: transformedArgs, resourceUID: targetUID } };
        }

        // Else, it returns an object that matches
        // what the entity-response's resolvers expect
        return { value: data };
      };
    },
  };
};