Vulcan/packages/vulcan-posts/lib/custom_fields.js

import Users from "meteor/vulcan:users";

Users.addField([
  /**
    Count of the user's posts
  */
  {
    fieldName: "postCount",
    fieldSchema: {
      type: Number,
      optional: true,
      defaultValue: 0,
      viewableBy: ['guests'],
    }
  },
  /**
    The user's associated posts (GraphQL only)
  */
  {
    fieldName: "posts",
    fieldSchema: {
      type: Array,
      optional: true,
      viewableBy: ['guests'],
      resolveAs: 'posts: [Post]'
    }
  }
]);