GraphQL integration (and API/data fetching in general) becomes quite repetitive and complex as our app scales. New features need to be built that are sort of similar to features that already existed, but what bits they can reuse is not clear (eg: pagination). New members join the team and we’d like them to work on their UI components without worrying about the data fetching logic of the rest of the component tree. Relay takes an opinionated stance to solve some of these problems that are worth understanding and learning from. In this talk, I'm going to motivate the core features in Relay from the ground-up. I'll do hands-on demos to explain the common challenges GraphQL clients run into, how one would fix them without Relay and then fix them with Relay. I'll also touch upon how Relay works and its design briefly and how Relay’s design goal is not just being a high-performance GraphQL client, but also increasing developer productivity and happiness.
How I Went from Being Skeptical about Relay to Falling in Love with It
AI Generated Video Summary
This Talk discusses the use of Relay and fragments in data fetching for React applications. It explores the challenges of fetching data from components and the optimization of data fetching. The Talk also covers the use of fragments for component data fetching and the challenges and potential errors that can arise. It highlights the design decisions of Relay that make data access easier and the use of variables in fragments. The Talk concludes with a discussion on refetching fragment data and the combination of fragments and queries in Relay.
1. Introduction to Relay and Hasura
I'm going to talk about falling in love with Relay, my journey from skepticism to admiration. I'll introduce myself as the founder and CEO of Hasura, an open source technology startup. Hasura provides a GraphQL engine that connects to your database and services, offering a unified GraphQL API. Relay handles the responsibility of achieving the best data fetch while using GraphQL. I'll use a data dashboard example to demonstrate the power of Relay in a React application.
Hello, everyone. I'm super happy to be here. I hope you all are doing fine. I'm going to talk a little bit about falling in love with Relay. So this is my journey of kind of being skeptical about Relay as a GraphQL client and then gradually falling in love with it.
My name is Tanna Gopal, and before I get started, I'll give you a quick introduction. So I'm the founder and CEO at Hasura. Hasura is an open source technology startup. We build a GraphQL engine that can connect to primarily your database and other services so that you can kind of stitch across them and get a unified GraphQL API. It runs as a docker container in your own infrastructure. It's open source under the Apache license, and you can check it out on GitHub. A lot of this work and this talk has been kind of motivated by the fact that we've been adding Relay support in Hasura, and towards the end I'll show you how you can kind of get started playing around with Relay and Hasura.
All right, so let's dive into Relay. When you think about GraphQL and you think about integrating GraphQL into your applications, the biggest selling point of GraphQL is that, at least for me, was that it was for the first time an API that I found easy to explore and integrate, right? So it was like I can kind of look at the way the API is, I can autocomplete it, I can look at the, you know, I can understand how I need to integrate the API because I can look at the types, right? I can integrate that with my type system, whatever I'm using on the client side. And stuff like that. Where Relay fits in is that Relay handles the responsibility or Relay makes it easy for us to achieve the theoretical best data fetch, right? That we can possibly achieve while using GraphQL and staying sane. So I'm going to talk about the staying sane aspect, right? So how can, while using GraphQL in our app, right? What is the best possible data fetching that we can do while introducing the least amount of burden on ourselves as developers, right? So that's kind of where Relay fits in. And this is going to become more clear as we go along and this is why Relay is amazing and the ideas behind Relay are really amazing.
So to kind of motivate or kind of look at one example through this talk, what I'm going to do is take the example of a data dashboard, right? So this is a front-end application. It's a React app. It's a data admin dashboard, right? So you can see that there are tables on the left. I'm looking at a particular table. That table has columns, that table has a filtering option, right? There's stuff like that. This app is actually the Hasura console, which is a React app. But in any case, imagine that this is a fairly, like medium complex, React application, just because there's a lot of data fetch happening. So if you look at the red boxes that I've kind of highlighted here, let me just bring in my pointer. If you look at these red boxes that I've highlighted here, right, those are kind of the different pieces of data that we're fetching from our API. So here we're fetching a list of all of the tables, right? Here we're fetching information about that particular table. We're only displaying the table name here. Here we're fetching a list of all of the columns so that we can render this dropdown and the column type so that we can render the operations that you can filter on that column.
2. Fetching Data for Table View
Here I'm fetching a list of columns to render a table view. In the modified table view, I'm looking at different columns and their types in the database. I'm also fetching a list of attributes and, for one attribute, a larger amount of data. To fetch this data and build the app, I would attach a query to each UI component.
Right. And here I'm fetching a list of all of the columns so that I can render a table view. Right. So those are kind of the different pieces of data that I need to fetch for this application.
Let's look at another view in the same application. So now I'm on a different view. I'm on the modified table view. Right. So here what I'm looking at is I'm looking at the different columns and the types of those columns in my database. Right. So I'm listing out all of the different columns. I'm listing out what the types of those columns are. Right. Whether it's a text column or a character column or is it nullable. And then in one case, one of the columns that I have clicked on as a user, I have an expanded view. So in this expanded view, I'm not looking at just two properties of this column. I'm looking at like five different properties of this column. Right.
So I'm fetching a list of attributes. But for one of those attributes, I'm fetching a larger amount of data. Right. Again, a fairly typical scenario that you can kind of imagine in an application. Right. All right. So let's see how we would have used a GraphQL API to fetch this data and build this app. Right. The first cut, the simplest thing to do is I would have just taken every single UI component and attached a query to it. So I make a query here to fetch the tables. I make a query here to fetch the table name for a particular ID. Right.
3. Fetching Data from Components
I'm fetching data from different components, which results in multiple queries. This approach is easy but terrible because it leads to a large number of network calls and redundant queries.
Maybe I'm getting this ID from the URL or from a particular component that was clicked on. Right. From this component that was clicked on. Then I make another component for this filter column, kind of UI that I have, where I fetch the columns name and the type. And here for this kind of table browser, I'm making a query to fetch the columns names. Right. So I'm making different queries. It's really easy because all of the data that I need to fetch is at the component level. Right. So the benefit is of having one query per component is that, you know, it's super easy. Right. It's modular, quote, unquote. This is actually, of course, in fact, it's a terrible idea because you're making a tremendous number of network calls and defeats the whole purpose. And, you know, things that people say about GraphQL. In fact, it's not just making many network calls. If you look at this UI carefully, you'll see that I'm making a lot of redundant calls. Right. I'm taking the name here, which I've kind of already fetched here and fetching the column names and types here, which I've already fetched here. So I'm making redundant queries as well. Right. Apart from the fact that I'm making multiple queries, which is terrible. Right.
4. Optimizing Data Fetching
The first optimization is to make one gigantic query that fetches all the necessary data for the page. While this is theoretically the best query, it becomes inconvenient for developers building different components as the data requirements for child components are scattered in ancestor components. Passing props to child components becomes cumbersome.
So. So the first optimization that I can do. Right. The simplest optimization that I can do is make one gigantic query. So I make one gigantic query for this page. Right. And this is theoretically the best query I can make. Right. So I make a query. I fetch all of the tables in their name for a particular table that I want to render. I fetch the table name and I fetch the kind of columns, you know, the names of the columns that I'm going to show here in the table browser and the types that I'm going to use for showing the different operators. Right. So if it's an integer, I can do equals. I can do equals if it's a Boolean, I'll show is true, is false like whatever. So. So this is kind of an optimal query that I can make. This is nice. Right. This is good, but I don't like this idea because even though it's optimal, as a developer that's building like that, as a developer who's kind of building these different components, it's inconvenient because the data requirements for a child component, right. Like for example, a filter column UI or a data browser UI, the requirements of that data are kind of somewhere in the ancestor. Right. It's somewhere in the ancestor component that has, that has this, that is kind of making this query. Right. And then I'm going to pass on all of the props to all of the child components gradually. Not a terribly kind of fun experience. Right.
5. Introducing Fragments for Component Data Fetching
I can introduce fragments instead of having a gigantic query at the top level. Each child component can have its own fragment that specifies the data it needs. For example, the table header component can declare a fragment for the name, while the filter UI can have a fragment for the columns and types. This allows for more granular control over the data fetched for each component.
So the next thing I can do is introduce fragments. Right. So what I can do is instead of having a gigantic query at the top level, I'll have a query at the top level that refers to different fragments that I have. Right. So whenever I build a child component, so let's say I'm building the table header component. I declare a fragment that says, here's a fragment, I want the name. Right. If I'm building the filter UI, I'll say, well, here's a fragment. I want all of the columns, the names of the columns and the types. Right. So I can render this UI. If I'm building this table browser component, I basically just fetch the names of the columns. That's all I need to, to kind of create this table header. Right.
6. Using Fragments in Component Building
I declare fragments alongside the components I build. Every component can declare the exact data it needs. However, using fragments can be error-prone. Two pain points are importing fragments and child components accessing all data. For example, a child component for voting on comments needs to be included in the parent fragment.
So I declare these fragments kind of alongside the components that I build. Right. So let's say I have three files here, in each of these files I include a fragment. Right. Also, if I'm building the ancestral component, I'll kind of go to the ancestor query component somewhere. Right. Even though these components have a hierarchy. I have to include, you know, this fragment in the ancestor component here or something like that. Right. So that's kind of what, what, what the fragment experience would look like.
So the pros here are that it's nice because, you know, every component that I'm building, I can declare the data. I can declare exactly the data that I want. The cons though, is that the experience of actually using fragments is not particularly great. And it is frequently error prone. I'm going to talk about two particular pain points in just basic vanilla integration of fragments. Right. The first is importing fragments. And the second is that all child components will get access to all of the data. So let's just take a look at what this means.
Right. So the first, and this is an example that I've taken from the Apollo client fragments documentation page. If you look at the left here, I'm making, I have a child component. So imagine this is comments and comments have votes. Right. And so what I'm looking at is, I'm looking at the child component where I'm voting on a particular comment. So this has a fragment. Right. And then the parent has the entire query, or maybe a parent fragment, right? It has a larger fragment that includes this fragment. Right. So this, this part is necessary, right? I need to, I need to include my child fragment in the parent fragment.
7. Importing Fragments and Potential Errors
This is the part that is a little bit irritating. I need to include an import this fragment as a variable inside this fragment. This is not fun because I have to make sure to include the fragment inside my components and also import it in the parent component, which can lead to errors.
Right. But this is the part that is a little bit irritating. Right? I need to declare, I need to include an import this fragment as a variable inside this fragment. This is irritating, right? This is not fun. Because now I have to kind of make sure that not only do I include the fragment inside my components, but then I also, whenever I'm writing the parent component, I'm kind of importing the, I'm importing that fragment as well and including that fragment here as well, right? Which I may forget to do, or, you know, all kinds of things can happen. There could be errors.
8. Challenges with Fragment Usage and Passing Data
If I have fragments that I include at the top level query, all components will have access to more attributes than they need. Passing props to child components requires care to avoid errors. To make fragments easier, we need automatic import and validation, as well as optimizations for passing data.
Right. So those are kind of the, it's, it's not an ideal experience. Right.
There's another pain point. The other pain point is that if I have fragments that I include at the top level query, what will happen is that all of these components, the React components where let's say, I fetch these components and I assign a variable to them to fetch the table data, right? When I, when I, when I fetch this data and I assign it a variable, this component will actually end up having access, not just to the name attribute that it needs, but also to the columns attribute and also to columns dot name and columns dot type. Right.
And if I look at the columns filter component that needs only name and type, this is fine. I'm going to have access to columns dot name and columns dot type, but the column browser thing, which only needs access to column name, will also end up getting access to column type. Right. And I have to be careful with the way I pass these props to my child components, from the parent query that I have. Right. And it requires a little bit of care. And if I don't take care, what can often happen, especially as we're building applications quickly, you know, let's say I'm building this browser component and I realize I need access to column type. Maybe it forget to update the fragment. Right. Maybe I need to go to tables dot table dot columns dot type anyway, because I have access to that. Right. Because of some other fragment that I was using. I'd be lazy. Right. Or I might be lazy and I might forget to kind of include that attribute in this fragment here. Right. Just because somebody else was requesting for it. And this is going to be the starting point of errors as soon as we have a large number of fragments. So if you want to make fragments easier, what we really want to do is make sure that fragments get automatically imported and validated as we use them in our components. And we also want the kind of optimizations to happen when we're passing down data. Right. So that we're getting some kind of isolation and modularity in the components that we're writing. Right. So that when I feel like I'm writing a component for a fragment, I feel like I have only I only have access to the data that I declared in my fragment.
9. Relay's Design Decisions for Data Access
Relay has two design decisions that make it easy to access data. First, it has a compiler that runs as a build-step, ensuring that all fragments are imported and validated at build time. Second, when using a fragment in a component, only the data that is accessible can be used. This provides a convenient way to work with fragments in Relay.
Right. And apart from that, I don't have access to any more data. Unless it's explicitly passed down to me from the parent component. Right. And so if you look at Relay, it has two design decisions that make this quite easy. The first is that Relay is not just a GraphQL client that is a library that you can kind of include, create GraphQL queries and make GraphQL queries with, but Relay also has a compiler that makes it possible to make it possible for the compiler basically kind of runs like as a build-step. Right. It's running in parallel as you're doing a development workflow. And as you're kind of building fragments and importing fragments inquiries all of the query, all of the fragments getting imported, all of the fragments getting validated is all kind of happening at build time so that I don't get these runtime errors with fragment imports. Right. Or for example, when I think about data masking, when I use the fragment in my component, I can only use the data that I have access to, which is the way that I use the fragment container inside Relay. Right.
10. Using Fragments and Introducing Variables
When using fragments with Relay, I don't need to explicitly import them in my parent fragment or query. I only have access to the attributes declared in my fragment. This ensures that I get the data I need and prevents errors. However, as I start using fragments, I'll soon need variables in my fragments. For example, in a dashboard, I may want users to choose certain options.
To kind of tangibly look at the work that gets removed from me. I do not have to explicitly import fragments in my parent fragment or in my parent query. And when I try to access the data that that my particular component will get. Right. I will only have access to those attributes that I've declared in my fragment. Right. So here I get access only to table.name. Here I only get access to columns.name and columns.type. And here I'll only get access to columns.name again. Right. Which is nice because if I try to access some other property I'll get a build time and a compile time error. Right. Which is neat. Right. So which is which is when you use kind of fragments with relay this will kind of start working for you automatically. Right. I didn't want to get into more syntax to show you what the setup is like but just wanted to stress on the concepts that you that you'll be able to use. All right.
The next problem that you run into as you start using fragments. Right. So fragments are nice. I'm using fragments everywhere. It's great. My components are modular. Right. But the next problem that I run into is going to be that I will soon need variables in my fragments. Right. So what I'm going to need is let's talk about a simple example. Let's say that in this kind of dashboard that I have. I want I want the users to choose.
11. Using Variables in Fragments
You want the users to be able to see only the first three columns. If you want to use a variable in a fragment, you need to declare it at the top level, which can be inconvenient because these variables belong deep down in the component hierarchy and come through user input.
You know I want the users to be able to see only the first three columns. Maybe I have like 1,000 column table. Right. And I only want to see the first three columns. Right. So maybe I want to do a limit which is I want to do some kind of a limit or in relay terminology you would say you'd call it like you'd want just the first three. Right. You want only the first three columns. Right. And and if that's what you want, you'll notice that you need to have a variable that this particular fragment has. Right. So maybe this particular component has something like a UI that says, you know how many columns do you want to see? I want to see three. I want to see ten. So I choose a number of columns that I want to see and then that becomes a user given kind of variable. Right. To do the fragment.
The thing is, this is obviously possible to do. This is valid syntax. But if I want to use a variable in a fragment, I need to declare it at the top level. Right. That means that if I need to use a variable in a fragment somewhere deep in my kind of child in my component hierarchy, I need to declare that variable at the top level query. Right. Because I need to declare query variables, which is, as you can imagine, a little bit irritating. Right. Because these variables kind of belong somewhere deep down in the component hierarchy. These variables come through user input. These variables kind of don't belong in an ancestor component. Right. Imagine if you were back to our original query based design. Right.
12. Declaring Variables for Fragments Locally
If you had one query per component, I'd be making a stupidly large number of fetches, but I would be able to declare exactly the variables that I need. I would like to declare variables for my fragments locally, at the fragment level, and use them there. Relay provides a design concept of having arguments and argument definition, which allows you to locally define and declare a variable in a fragment without modifying the top level query. This is really neat.
If you had one query per component, I'd be making a stupidly large number of fetches, but I would be able to declare exactly the variables that I need, you know, when I need them. Right. Which is, which is cool. So if, if the way this works in relay is, the way this works in relay is what I would like to do is kind of be able to declare variables for my fragments locally. Right. I would like to declare them at the fragment level and I would kind of like to use them at a fragment level as well. And this is where a relay design concept of having arguments and argument definition. These are client side directives and two client said directives that you can add to any fragment to kind of locally define and declare a variable, then and there, right. At the fragment level without having to go the top level query and modify that. And that is really neat. And we look at an example soon. Right. And we look at an example of what the syntax looks like soon. But for now, in the next, in kind of the next UI example that we look at.
13. Handling Variables Locally and Updating Fragments
We need a way to handle variables locally and update fragments when the user provides input. For example, when paginating through a list, the variables used to fetch the list change, and we want to refetch the list without running the entire query again. This desire for queries almost for each component leads to the need for modularity of fragments and the independent lifecycle ability of queries.
But for now, bear in mind that we need some way of being able to handle variables locally. Right. So as soon as you realize that you want to handle variables locally, you realize that actually what you wanted to do was whenever the user is kind of providing input somewhere deep down in the component hierarchy, right, what you want to do is you want to update that fragment. Right. So if you look at that kind of example where I wanted to view just three columns, maybe the user will kind of provide us more input, and I want to view just 10 columns. And as the user is kind of providing input to us, we want to update just that fragment and we don't want to rerun, we definitely do not want to run the entire query again. Right. That's kind of what we want to do. Right. So we want to use the modularity of fragments. But we want kind of the independent lifecycle ability almost of a query. Right. And let's take a look at a slightly more tangible example. Right. So, in applications that you're building, you would frequently see this when this comes for pagination. Right. When you want to kind of paginate through, you have a child component that is rendering a list. Right. And then as you paginate through it, the variables that you're using to fetch that list, those variables are changing. Right. And those variables are changing on demand. Now when those variables are changing, you want to refetch the list. You don't want to run the entire query again. Right. So, that is the kind of thing that I was talking about, which is kind of like an expand use case. Right. Or read more kind of use case. And just like I said, this is like wanting the desire for having queries almost for each component. Right. So, so let's look at a let's look at a tangible example and what the queries look like.
14. Fetching Expanded Attributes
I have a list where I want to view more information about an attribute when the user clicks on expand. By default, I only want two attributes for each list element, but if expanded, I want five attributes. I'm running a query to fetch all the columns, where I fetch minimal information like name and description. If an element is expanded, I want to show additional attributes. This is achieved by defining a variable at the fragment level and using argument definitions. On the first load, the default value is false, and when the user clicks on expand, the fragment is rerun.
So here I'm now looking at an example, similar example of where I have a list. Right. And one item of the list, whenever the user clicks on expand. Right. I want to view more information about this attribute. So by default, I only want two pieces, two attributes for list element. And if I expand it, I want five attributes for that list element. Right. And this is for further for the dashboard that we're building. Right.
So if I think about this, what I want to do is what I want to be able to do is sorry, what I want to be able to do is I want to run a query to fetch all of the elements. In my in this case, the elements are columns. So I want to fetch all of the columns. Right. So for instance, I want to fetch I want to fetch minified like minimal information per column. So let's look at what the minimal information here is. I only want to fetch name and description. So these are the two attributes that I want to show. In case one of the elements is expanded. I want to be able to show expanded information, right. For that particular for that particular column, right. And so now let's look at the expanded way. I want to see name. I want to see like 10 other attributes, right. And this is a variable that's kind of locally, that's kind of defined at this fragment level, right. So I'm using argument definitions to define a variable at this fragment level to say, while rendering this list, right. If this variable happens to be true for this particular column, I want to also include this particular fragment, right. Now on the first load, on the first load, our default value is going to be false. So on the first load, we're going to fetch all of the elements with just name and description. When the user clicks on expand, that's when I want to, that's when I want to kind of rerun this fragment, right.
15. Rerunning and Refetching Fragment Data
I want to rerun and refetch the data for a fragment only if it is expanded. This can be achieved by making the fragment re-fetchable and using the refetch function with the variable set to true. The fragment will run as a query with the variable set to true, allowing for the retrieval of specific data. This process occurs when the fragment is expanded.
But fetch more data for this fragment. Right. That's, that's kind of what I want to do, right, I want to rerun and rerun, refetch the data for this particular fragment, only if we expand it is true to fetch more data, right. And, and we'd really, that is as simple as going to a particular fragment and saying, let's make this fragment re-fetchable. And whenever there's a click or a user event, we'll run a function called refetch, which is a function that you have on a fragment with the variable set to true. So this fragment is going to run as a query, right. It's going to run as a query with this variable set to true so that you can fetch exactly this data, right. And that is going to happen just for that one column, right. One instance where I click on expand, right.
16. Fragment Re-fetching and Relay API
Fragments in Relay cannot run in isolation and need to be part of a larger query. To enable fragment re-fetching, a Relay-compatible API implements a node interface with a globally unique ID. When a fragment is re-fetched, the client only runs the query for that specific element, using the unique ID and requested fields. This approach combines the convenience of using fragments with the ability to treat each fragment like a query.
And this is really interesting, right. This is, if you think about the way it works underneath, if you think about the ergonomics, it's like, oh, this fragment is like a query, so I can run this query again. That's a convenient thought process, right? But in reality, it's not easy to kind of make that work because a fragment can't run in isolation, right? A fragment needs to run as a part of a larger query. So how can a fragment run by itself? And the secret here is that a Relay API would typically implement a node interface and a root resolve of any node. So a Relay compatible API, well, it's not compulsory anymore, it's kind of optional, is that every element that you're fetching has an interface or implements an interface called a node and it has a globally unique ID, right? And your Relay GraphQL API has a root resolver to fetch any node just by its kind of GUID, its globally kind of unique ID. So what Relay can do is that when I mark or when I request the client to re-fetch a particular fragment, the client doesn't have to run the entire query again. The client just reruns the query for that particular column or that particular element that I wanted to rerun. And the client is able to do that because every element is an instance of node and every element has a unique ID. So the query that's kind of running in the background is actually query, element, unique ID and the exact fields that I want. So in our particular example, there's a background query that runs whenever we do a refetch. The query that's running, the underlying GraphQL query that's running is a query on column where ID equal to the current ID for this column that I'm rendering, which is a geo ID that I have. And it's fetching the fields name, description, type, nullable, unique, default, whatever. Like it's fetching whatever different attributes that I want. And this is really nice. I get the convenience of using fragments, right? But at the same time, I get the ability to kind of use, I get the ability to kind of treat each fragment like a query. And this is really convenient.