post.component.ts

import { Apollo } from 'apollo-angular';
import gql from 'graphql-tag';

interface Post {
  id: string;
  text: string;
}

interface PostQuery {
  post: Post;
}

@Component({...})
export class PostComponent {
  @Input() postId: string;
  post: Observable<Post>;
  
  constructor(private apollo: Apollo) {}
  
  ngOnInit() {
    this.post = this.apollo.watchQuery<PostQuery>({
      query: gql`
        query getPost ($id: String!) {
          post(id: $id) {
            id
            text
          }
        }
     `,
     variables: {
       id: this.postId
     }
   })
     .valueChanges
     .pipe(
       map(result => result.data.post)
     );
  }
}