| --- |
| id: caching |
| title: Caching Examples |
| --- |
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| > Please thoroughly read the [Important Defaults](../important-defaults.md) before reading this guide |
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| ## Basic Example |
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| This caching example illustrates the story and lifecycle of: |
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| - Query Instances with and without cache data |
| - Background Refetching |
| - Inactive Queries |
| - Garbage Collection |
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| Let's assume we are using the default `gcTime` of **5 minutes** and the default `staleTime` of `0`. |
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| - A new instance of `injectQuery(() => ({ queryKey: ['todos'], queryFn: fetchTodos }))` initializes. |
| - Since no other queries have been made with the `['todos']` query key, this query will show a hard loading state and make a network request to fetch the data. |
| - When the network request has completed, the returned data will be cached under the `['todos']` key. |
| - The date will be marked as stale after the configured `staleTime` (defaults to `0`, or immediately). |
| - A second instance of `injectQuery(() => ({ queryKey: ['todos'], queryFn: fetchTodos })` initializes elsewhere. |
| - Since the cache already has data for the `['todos']` key from the first query, that data is immediately returned from the cache. |
| - The new instance triggers a new network request using its query function. |
| - Note that regardless of whether both `fetchTodos` query functions are identical or not, both queries' [`status`](../../reference/functions/injectquery.md) are updated (including `isFetching`, `isPending`, and other related values) because they have the same query key. |
| - When the request completes successfully, the cache's data under the `['todos']` key is updated with the new data, and both instances are updated with the new data. |
| - Both instances of the `injectQuery(() => ({ queryKey: ['todos'], queryFn: fetchTodos })` query are destroyed and no longer in use. |
| - Since there are no more active instances of this query, a garbage collection timeout is set using `gcTime` to delete and garbage collect the query (defaults to **5 minutes**). |
| - Before the cache timeout has completed, another instance of `injectQuery(() => ({ queryKey: ['todos'], queyFn: fetchTodos })` mounts. The query immediately returns the available cached data while the `fetchTodos` function is being run in the background. When it completes successfully, it will populate the cache with fresh data. |
| - The final instance of `injectQuery(() => ({ queryKey: ['todos'], queryFn: fetchTodos })` gets destroyed. |
| - No more instances of `injectQuery(() => ({ queryKey: ['todos'], queryFn: fetchTodos })` appear within **5 minutes**. |
| - The cached data under the `['todos']` key is deleted and garbage collected. |
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| For more advanced use-cases, see [injectQuery](../../reference/functions/injectquery.md). |
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