schema {
  query: Query
  mutation: Mutation
}
type Blog {
  id: ID!
  eventName: String
  eventUrl: String
  eventStartAt: String
  eventEndAt: String
  posts: [Post]
}
input CreateBlogInput {
  eventName: String
  eventUrl: String
  eventStartAt: String
  eventEndAt: String
}
input CreatePostInput {
  blogId: ID!
  name: String!
  body: String!
  imageUrl: String
}
input DeletePostInput {
  id: ID!
}
type Mutation {
  createBlog(blog: CreateBlogInput): Blog
  createPost(post: CreatePostInput): Post
  deleteBlog(id: ID!): Blog
  deletePost(post: DeletePostInput): Post
  updateBlog(blog: UpdateBlogInput): Blog
  updatePost(post: UpdatePostInput): Post
}
type Post {
  id: ID!
  name: String!
  body: String!
  blog: Blog
}
type Query {
  user(id: ID!): User
  blog(id: ID!): Blog
}
input UpdateBlogInput {
  eventName: String
  eventUrl: String
  eventStartAt: String
  eventEndAt: String
}
input UpdatePostInput {
  id: ID!
  name: String
  body: String
  imageUrl: String
}
type User {
  id: ID!
  firstName: String!
  lastName: String!
}

const getSchemaTypeField = (schema, typeName, fieldName) => {
  const type = schema.getType(typeName);

  if (type === undefined) {
    throw new Error('"' + typeName + '" type does not exist in the schema.');
  }

  const fields = type.getFields();

  const field = fields[fieldName];

  if (field === undefined) {
    throw new Error('"' + typeName + '" type does not have "' + fieldName + '" field.');
  }

  return field;
};

const addResolveToSchemaMethod = (schema, typeName, fieldName, resolveFunction) => {
  const field = getSchemaTypeField(schema, typeName, fieldName);

  field.resolve = resolveFunction;
};

addResolveToSchemaMethod(schema, 'Query', 'user', () => {
  return {
    id: '2'
  }
});

addResolveToSchemaMethod(schema, 'User', 'id', () => {
  return '3';
});