react-query/docs/framework/angular/guides/placeholder-query-data.md

metadata

id: placeholder-query-data
title: Placeholder Query Data
ref: docs/framework/react/guides/placeholder-query-data.md

class TodosComponent {
  result = injectQuery(() => ({
    queryKey: ['todos'],
    queryFn: () => fetch('/todos'),
    placeholderData: placeholderTodos,
  }))
}

class TodosComponent {
  result = injectQuery(() => ({
    queryKey: ['todos', id()],
    queryFn: () => fetch(`/todos/${id}`),
    placeholderData: (previousData, previousQuery) => previousData,
  }))
}

export class BlogPostComponent {
  // Until Angular supports signal-based inputs, we have to set a signal
  @Input({ required: true, alias: 'postId' })
  set _postId(value: number) {
    this.postId.set(value)
  }
  postId = signal(0)
  queryClient = inject(QueryClient)

  result = injectQuery(() => ({
    queryKey: ['blogPost', this.postId()],
    queryFn: () => fetch(`/blogPosts/${this.postId()}`),
    placeholderData: () => {
      // Use the smaller/preview version of the blogPost from the 'blogPosts'
      // query as the placeholder data for this blogPost query
      return queryClient
        .getQueryData(['blogPosts'])
        ?.find((d) => d.id === this.postId())
    },
  }))
}