React-query 시리즈 파트 2: QueryClient 구성.

In this part, we will briefly talk about the configurations settings object queryClientConfig we saw earlier. We will also look at what each key-value pair in the configuration does for our queries and mutations.

You remember this snippet from the last post ?

import { QueryClient, QueryClientProvider } from 'react-query';

const queryClientConfig = {
    defaultOptions: {
      queries: {
        retry: 2,
        staleTime: 1000 * 30,// 30seconds
        cacheTime: 1000 * 30, //30 seconds
        refetchOnMount: "always",
        refetchOnWindowFocus: "always",
        refetchOnReconnect: "always",
        refetchInterval: 1000 * 30, //30 seconds
        refetchIntervalInBackground: false,
        suspense: false,

      },
      mutations: {
        retry: 2,
      },
    },

 ...

The queryClientConfig object provides us with the ability to tweak and override the default behavior of react-query library or to put it better; it enables us create our custom defaults both for queries and mutations across our application. This global configuration can also be overridden for each query or mutation instance in our application if need be (We will see how in the next article). Nested in the queryClientConfig object, is the defaultOptions object, which in turn has two objects; queries and mutations nested in it. The key-value pairs in these two objects( queries and mutations ) are what we will be talking about.

The retry option takes either a boolean , number or function as it's value. When false , our unsuccessful queries are not retried by default.
Passing in a true value ensures that our queries are retried infinitely (i.e. continued retries until the query gets successful).
When retry is given a number value, failed queries will retry until the failed queries count meets that number.
retry do also take a function as it's value. This function receives a failure count(number) and error as it's first and second argument respectively. This function must return a boolean to determine whether a query should be retried or not.

...

//function as value for retry

const queryClientConfig = {
    defaultOptions: {
      queries: {
        retry: (failureCount, error) => {
           //...do something with passed argument
        }
       ...
      },
    },
 ...

function as a value of retry is aimed at giving us more granular control to determine ourselves if a query should be retried based on the number of failed attempts, type of error or both.

staleTime is time in milliseconds after which the returned data from a successful query is considered stale. staleTime accepts either a number or Infinity as it's value. Infinity as a value ensures that our data is never considered stale. When staleTime receives a number , the number is calculated as time in milliseconds after which the data is considered stale.

The cacheTime options receives either a number or Infinity as a value. It is the time in milliseconds that an unused/inactive cached data is allowed to remain in memory. When a cached data becomes unused or inactive, it will be cleaned-up from the memory after this duration. When different cache times are specified, the longest one will be used.
If cacheTime is set to Infinity, cached data are never cleaned from memory.
When cacheTime receives a number as it's value, this number is calculated as time in milliseconds after which, inactive/unused cached data is purged from memory.

When a component mounts and a query is run for the first time, the returned data from this successful query is cached. Sometimes, we may not want this same query to run again if the component remounts and the returned data from the previous call is still exists and fresh in the cache; this is the control refetchOnMount gives us.
refetchOnMount accepts a boolean or the string : "always" as it's value.
If set to false , the query will not refetch on component mount by default.
If value is set to true , the query is refetched if the data in cache is considered stale.
"always" as it's value will ensure that query is refetched regardless of whether cached data is stale or not.
(Refer to staleTime to know when data is considered stale).

This option is similar to refetchOnMount but for window focus.
We may wish to show our users fresh data whenever they switch their focus back to the browser tab where our application is being used; refetchOnWindowFocus helps with this.
It accepts similar values as refetchOnMount : boolean or the string , "always" .
When refetchOnWindowFocus is set to false , query will not be refetched on window focus. When set to true , query is refetched only if cached data is stale. "always" will cause queries to refetch regardless of whether cached data is stale or not.

While using our application, users may lose internet connection. During this period, long or short as it may be, remote data may have changed.
refetchOnReconnect gives use the control to determine whether we want our application to refetch queries once our users regain internet connection.
refetchOnReconnect accepts a boolean or the string , "always" . By now, you can guess where this is going 😉.
With false as a value, queries are not refetched on reconnection to the internet at all.
true lets queries refetch on reconnection only if the data is considered stale. (again, check staleTime to understand when a cached data is considered stale).
"always" will ensure queries are refetched whether cached data is stale or not.

We may want our application refetching queries at certain interval in time regardless of whether data is stale or not. This is very useful for rapidly changing remote data or for near real-time behavior for our application.
refetchInterval accepts either false or a number as it's value.
false means that our queries will not refetch at interval.
When a number is passed to refetchInterval as a value, this number is calculated as time in milliseconds. For example, 5000 as a value of refetchInterval means queries will be refetched every 5 seconds.

Would you like explicitly control the refetchInterval behavior for when users are not focused on our application ? refetchIntervalInBackground lets us do this. It accepts only boolean values.
true as a value implies that queries will be refetched at interval (as set on refetchInterval ) even when our application is not in focus. When false , queries will not refetch at interval when our application is not in focus.

suspense accepts only boolean values.
When set to true , active queries will suspend and will throw a runtime error if an error occurs.
With false , active queries will neither suspend nor throw a runtime error if an error occurs.

Pheew 😤 if you have gotten this far, I'm grateful. I'm a little 😩 myself. Hang in there, we are almost done.

The mutations object lets us configure react-query behavior for our mutations. Mutations are for create/update/delete actions to our server. For any action that seeks to mutate our remote data, mutations should be used. Lets discuss the only item in the mutations object: retry .

retry as an option for the mutations object is similar to that for queries .
retry accepts either a boolean , number or function as it's value.
false as the value for retry ensures that failed mutations will not retry by default.
When true , failed mutations will retry infinitively(i.e. until a mutation is successful).
If set to an number , e.g. 3, failed mutations will retry until the failed mutations count meets that number.
function as a value for retry enables us decide ourselves, when we want failed mutations to retry. This function must return a boolean .

...

//function as value for retry in mutations

const queryClientConfig = {
    defaultOptions: {
       ...
      mutations: {
        retry: (failureCount, error) => {
           //...do something with passed argument
        }
      },
    },
 ...

This post was a long one and I really appreciate that you made it this far.
In the next part, we will discuss data fetching with the useQuery hook.
Thank you all for your support. Please give me a 💖 if this post or part of it has helped you. Comments are welcomed too.
Follow me on