We then create an instance of Store, which will hold the cached data. The next thing we do is set up a network interface using the fetch client to call our GraphQL API. Finally, we export our Relay environment to use it in other modules. Firstly, and in very simple terms, Relay is the data framework that lives inside the app, and GraphQL is a query language used within Relay to represent the data schema.

Fetching data is hard, dealing with ever-changing data is hard, and performance is hard. Relay aims to reduce these problems to simple ones, moving the tricky bits into the framework and freeing you to concentrate on building your application. URQL supports document caching for content-heavy pages and normalized caching for dynamic and data-heavy applications.

GraphQL is also run on a server separately from the app to provide a data source for Relay to interact with. To put it into simpler terms, we say that to pass the fragment data, we pass the object where the fragment is spread, and the component then uses this object to get the real fragment data. Relay, through its robust type systems, makes CompletableFuture in Java sure that the right object is passed with required fragment spread on it. At the same time, no component knows what data the other component needs except from the GraphQL type that has the required component data. Relay makes sure the right data is passed to the respective component, and all input for a query is sent to the server.

Global Object Identification

We have a community-maintained list of people and projects using Relay in production. File types are generated by Graphcool and have some special characteristics. It’s probable you’d otherwise re-create a lot of Relay’s caching, and UI best practices independently. While you work on a Relay project, the Relay compiler will guide you to ensure project-wide consistency and correctness against your GraphQL schema. Global Object Identification consists on providing globally unique ids across your entire schema for every type, built using the Node GraphQL interface.

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react graphql relay

That said, there are libraries that can help you generate GraphQL from your models for every popular language. Checkout the list awesome-graphql to see what libraries ASP NET MVC Developer Job Description Template are available. By the end of this chapter you’ll understand what Relay is, how to use it, and have a firm foundation for integrating Relay into your own apps.

This means that a component depends on some fields from the user type, irrespective of the parent component. In the example above, the component will render an avatar using the fields specified in the Avatar_user fragment named. Another highly important client-side convention is colocation.

Why You Should Prefer Next.js 12 Over Other React Setup

It has a lot of features, such as data consistency, optimistic updates, type safety, optimized runtime, etc. There’s more to building an application than creating a user interface. Data fetching is still a tricky problem, especially as applications become more complicated.

react graphql relay

We’ve provided a Relay-compatible GraphQL demo server in the sample code with this app. In this chapter we aren’t going to discuss the implementation details of the server. If you’re interested in building GraphQL servers, checkout the chapter “GraphQL Server.” We have no data changes in this view, however if you want to learn more about how they work, please read the Relay docs on mutations. When we originally planned the app we discussed the choice of data layer and compared Redux with an alternative Facebook Open Source project called Relay.

Files

MORE POSTS BY THIS AUTHOR Sachin Pandey Full-stack Development Sachin is a Software Engineer at Velotio. The data return is kept in some framework-specific representation of the data store. When using Relay, components define their data requirement by themselves. These components can then be composed along with other components that have their own separate data. Fragments not only allow us to reuse the definitions but more essentially, they let us add or remove fields needed to render our avatar as we evolve our application. If we look at the sample fragment definition above, the fragment name, Avatar_user, is not just a random name.

react graphql relay

We will use this file for rendering each podcast that we fetch from our API. When the command is run the definitions are inserted into a __generated__ folder nested within the folder that contains the component. If the and components were in the folder src/components/Todo/ you would find the generated type definitions within src/components/Todo/__generated__. A simple importstatement will pull the definition in, and the type can be applied to the component’s props variable. What this translates to is a higher-order component provided by Relay called a Fragment Container. It relies on a named “piece” of a GraphQL query that is defined in a child component, then referenced in the parent GraphQL query.

Having the complete flexibility of JavaScript to construct your HTML is liberating. It allows for even more declarative ways to describe dynamic elements, and gives you the super power of modularity. Clean HTML templates matter far less than the performance of your applications.

Apollo

We want to query a list of podcasts and display them on our app. We don’t want to query all the podcasts, otherwise the API would take too long and the database would receive a lot of requests, which may cause a problem. We want to get a list of podcasts and paginate through them—very simple. The useLazyLoadQuery is the simplest hook for querying something with Relay.

Pros of Apollo Client

The simplest way to fetch query data is to directly call loadQuery. Apollo is good for teams with multiple development environments looking for a fully-featured “all-rounder” GraphQL client solution. Once you’ve installed URQL, you will need to import the following method to create a basic GraphQL client, as shown below. As you might have already realized, pluralsight web-dev-starter setting up and configuring Relay was not as straightforward as Apollo Client, but on the bright side, you only have to do the initial setup once. To learn more about Relay features such as Fragments, you can refer to the official documentation. We can then specify our query data by using the client.query() method with the query string, as shown below.

The idea for the useSubscription hook originated in an issue on that repo. Thank you @morrys for driving this project and for playing such an important role in our open source community. Only the fields of an object that a component explicitly asks for will be accessible to that component, even if other fields are known and cached in the store .

Relay’s mutation API supports making optimistic updates to show immediate feedback to users, as well as error handling and automatically reverting changes when mutations fail. Fragments cannot be fetched by themselves; instead, they must ultimately be included in a parent query. The Relay compiler will then ensure that the data dependencies declared in such fragments are fetched as part of that parent query. Relay automatically keeps all of your components up to date when data that affects them changes, and efficiently updates them only when strictly necessary. Relay handles the heavy lifting to ensure the data declared by your components is fetched in the most efficient way.

Once you’ve installed Apollo Client, you will need to import the following modules to make a basic query, as shown below. Get the rest of this chapter plus hundreds of pages of React instruction, 5 sample projects, a screencast, and more. In order to use Relay, your GraphQL server must adhere to a specific set of guidelines. We’re not going to talk about Apollo in this chapter, but it’s a fantastic library and it’s absolutely worth looking into for your app. Because Relay holds a central store of your data, this means it’s not really compatible with other data architectures that keep a central store, like Redux. You can’t have two central stores of state and so this makes the current versions of Redux and Relay essentially incompatible.

If the blogPost object did not have the correct fragment, i.e., BlogPostHead_blogPost, spread on it, we would have received a type error. Even if there were another fragment with exact same data selection spread on it, Relay makes sure it’s the right fragment that we use with the useFragement. This allows you to change the update fragment definitions without affecting other components. Basically, it’s a framework to manage these operations, and other data mechanics like pagination, filtering and sorting.

The blogPostHead_blogPost has the fragment type definitions, which is then passed to the useFragment hook to ensure type safety when using the data from the fragment. The other import, blogPostHead_blogPost$key, is used in the interface Props , and this type definition makes sure that we pass the right object to useFragment. Otherwise, the type system will throw errors during build time. In the above child component, the blogPost object is received as a prop and is passed to useFragment as a second parameter.

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