Fetching paginated posts

In the post service, we'll define and implement a getPostsByUserId() method that will be called by the profile component to retrieve paginated posts belonging to a certain user. As an assignment, we'll also implement a getFeed() method to retrieve the network's most recent posts, regardless of who posted them. Proceed as follows:

1. Open the core/services/post/post.service.ts file and add the following imports to it:

   import { Apollo } from 'apollo-angular';
   import {
     GetPostsByUserIdDocument,
     GetPostsByUserIdQuery,
     GetPostsByUserIdQueryVariables
   } from '@ngsocial/graphql/documents';

These imports were generated by the GraphQL code generator.

2. Inject the Apollo service, as follows:

   constructor(
     /* ... */
     private apollo: Apollo) { }

3. Define a getPostsByUserId() method, as follows:

   getPostsByUserId(
     userId: string,
     offset?: number...