How to chain 2 queries in RTK Query

In RTK Query, if you need to connect two queries, the common approach is to sequentially use the two query hooks within a component and determine the behavior of the second query based on the result of the first query. This ensures data dependencies and correct data flow.

Here I will provide a specific example to illustrate how to implement this process: Suppose we have a user list query useGetUsersQuery and a user details query useGetUserDetailsQuery based on user ID.

Step 1: Use the First Query

First, we use useGetUsersQuery to fetch the user list:

javascript
const { data: users, isError: isUserError } = useGetUsersQuery();

Step 2: Call the Second Query Based on the First Query's Result

Then, we can select the first user from the list (for simplicity in this example) and use its id to call the second query:

javascript
const firstUserId = users?.[0]?.id;

const { data: userDetails, isError: isDetailsError } = useGetUserDetailsQuery(firstUserId, {
    skip: !firstUserId   // Skip the query when firstUserId is undefined, which typically occurs when the first query hasn't returned results yet.
});

The key here is the skip option, which allows us to skip the query when firstUserId is undefined, which typically occurs when the first query hasn't returned results yet.

Implementing Dependency Updates

If the user list or the selected user ID changes, RTK Query will automatically re-initiate the useGetUserDetailsQuery because its dependency firstUserId has changed. This ensures that the user details data is always up-to-date.

Error Handling

In practical applications, we also need to handle potential error cases:

javascript
if (isUserError) {
    return <div>Failed to fetch users.</div>;
}

if (isDetailsError) {
    return <div>Failed to fetch user details.</div>;
}

if (!userDetails) {
    return <div>Loading...</div>;
}

return (
    <div>
        <h1>{userDetails.name}</h1>
        <p>Email: {userDetails.email}</p>
        // Other user details
    </div>
);

This example demonstrates how to connect two queries in RTK Query to handle more complex data dependencies and flows. This approach maintains code readability and maintainability while providing powerful data synchronization capabilities.