Query Keys

At its core, TanStack Query manages query caching for you based on query keys. Query keys have to be an Array at the top level, and can be as simple as an Array with a single string, or as complex as an array of many strings and nested objects. As long as the query key is serializable, and unique to the query's data, you can use it!

The simplest form of a key is an array with constants values. This format is useful for:

• Generic List/Index resources
• Non-hierarchical resources

// A list of todos
useQuery({ queryKey: ['todos'], ... })

// Something else, whatever!
useQuery({ queryKey: ['something', 'special'], ... })

When a query needs more information to uniquely describe its data, you can use an array with a string and any number of serializable objects to describe it. This is useful for:

• Hierarchical or nested resources
  • It's common to pass an ID, index, or other primitive to uniquely identify the item
• Queries with additional parameters
  • It's common to pass an object of additional options

// An individual todo
useQuery({ queryKey: ['todo', 5], ... })

// An individual todo in a "preview" format
useQuery({ queryKey: ['todo', 5, { preview: true }], ...})

// A list of todos that are "done"
useQuery({ queryKey: ['todos', { type: 'done' }], ... })

This means that no matter the order of keys in objects, all of the following queries are considered equal:

useQuery({ queryKey: ['todos', { status, page }], ... })
useQuery({ queryKey: ['todos', { page, status }], ...})
useQuery({ queryKey: ['todos', { page, status, other: undefined }], ... })

The following query keys, however, are not equal. Array item order matters!

useQuery({ queryKey: ['todos', status, page], ... })
useQuery({ queryKey: ['todos', page, status], ...})
useQuery({ queryKey: ['todos', undefined, page, status], ...})

Since query keys uniquely describe the data they are fetching, they should include any variables you use in your query function that change. For example:

function Todos({ todoId }) {
  const result = useQuery({
    queryKey: ['todos', todoId],
    queryFn: () => fetchTodoById(todoId),
  })
}

Note that query keys act as dependencies for your query functions. Adding dependent variables to your query key will ensure that queries are cached independently, and that any time a variable changes, queries will be refetched automatically (depending on your staleTime settings). See the exhaustive-deps section for more information and examples.

For tips on organizing Query Keys in larger applications, have a look at Effective React Query Keys and check the Query Key Factory Package from the Community Resources.