📄 tanstack/query/latest/docs/framework/angular/guides/dependent-queries

Dependent (or serial) queries depend on previous ones to finish before they can execute. To achieve this, it's as easy as using the enabled option to tell a query when it is ready to run:

// Get the user
userQuery = injectQuery(() => ({
  queryKey: ['user', email],
  queryFn: getUserByEmail,
}))

// Then get the user's projects
projectsQuery = injectQuery(() => ({
  queryKey: ['projects', this.userQuery.data()?.id],
  queryFn: getProjectsByUser,
  // The query will not execute until the user id exists
  enabled: !!this.userQuery.data()?.id,
}))


// Get the user
userQuery = injectQuery(() => ({
  queryKey: ['user', email],
  queryFn: getUserByEmail,
}))

// Then get the user's projects
projectsQuery = injectQuery(() => ({
  queryKey: ['projects', this.userQuery.data()?.id],
  queryFn: getProjectsByUser,
  // The query will not execute until the user id exists
  enabled: !!this.userQuery.data()?.id,
}))

The projects query will start in:

tsx

status: 'pending'
isPending: true
fetchStatus: 'idle'


status: 'pending'
isPending: true
fetchStatus: 'idle'

As soon as the user is available, the projects query will be enabled and will then transition to:

tsx

status: 'pending'
isPending: true
fetchStatus: 'fetching'


status: 'pending'
isPending: true
fetchStatus: 'fetching'

Once we have the projects, it will go to:

tsx

status: 'success'
isPending: false
fetchStatus: 'idle'


status: 'success'
isPending: false
fetchStatus: 'idle'

injectQueries dependent Query
-----------------------------

Dynamic parallel query - injectQueries can depend on a previous query also, here's how to achieve this:

// injectQueries is under development for Angular Query


// injectQueries is under development for Angular Query

Note that injectQueries return an array of query results

A note about performance
------------------------

Dependent queries by definition constitutes a form of request waterfall , which hurts performance. If we pretend both queries take the same amount of time, doing them serially instead of in parallel always takes twice as much time, which is especially hurtful when it happens on a client that has high latency. If you can, it's always better to restructure the backend APIs so that both queries can be fetched in parallel, though that might not always be practically feasible.

In the example above, instead of first fetching getUserByEmail to be able to getProjectsByUser, introducing a new getProjectsByUserEmail query would flatten the waterfall.

Edit on GitHub

Parallel Queries

Background Fetching Indicators

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