Recently mixing TypeScript and GraphQL is becoming a defacto standard of modern web development. However, there is not so much information of how to combine them without hassle.
In conclusion, I've found Fragment
first approach should painlessly work with TypeScript. Why? it accelerates type definition's reusability. Let's see how it works.
[edited]
I realized that Colocating Fragment is the best for GraphQL + TypeScript while trying to implement some real-world frontend projects (as freelance jobs). That pattern is a little verbose, but declarative and easily scalable. So instead of reading this article, you should read carefully: https://www.apollographql.com/docs/react/data/fragments/#colocating-fragments
[/edited]
Step 1 - No type
In the example from react-apollo, you can see the following code.
import { useQuery, gql } from "@apollo/client"
const EXCHANGE_RATES = gql`
query GetExchangeRates {
rates(currency: "USD") {
currency
rate
}
}
`
function ExchangeRates() {
const { loading, error, data } = useQuery(EXCHANGE_RATES)
if (loading) return <p>Loading...</p>
if (error) return <p>Error :(</p>
return data.rates.map(({ currency, rate }) => (
<div key={currency}>
<p>
{currency}: {rate}
</p>
</div>
))
}
It looks nice, but imagine the type of data
. Yes, it is any
. It breaks type-safety and you will go mad!
Note: technically not
any
butRecord
, although they are almost same in this context
Step 2 - Type manually
To avoid data
become any
, we can type the query result using TypeScript's generics feature.
import { useQuery, gql } from "@apollo/client"
interface GetExchangeRates {
rates: {
currency: string
rate: number
}[]
}
const EXCHANGE_RATES = gql`
query GetExchangeRates {
rates(currency: "USD") {
currency
rate
}
}
`
function ExchangeRates() {
const { loading, error, data } = useQuery<GetExchangeRates>(EXCHANGE_RATES)
if (loading) return <p>Loading...</p>
if (error) return <p>Error :(</p>
// Type signature of `data` is:
// {
// rates: {
// currency: string
// rate: number
// }[]
// }
return data.rates.map(({ currency, rate }) => (
<div key={currency}>
<p>
{currency}: {rate}
</p>
</div>
))
}
As you can see, this is so painful! Every time you update your query, you should manually update its interface too.
Step 3 - Type codegen
Fortunately, we can generate TypeScript's type definitions from GraphQL queries using apollo-tooling
.
https://github.com/apollographql/apollo-tooling#apollo-clientcodegen-output
Note: there are some tools other than apollo, but I prefer apollo because it is the most minimal one.
Let's execute some commands to create type definitions.
npx apollo client:codegen \
--localSchemaFile schema.gql \
--target typescript \
--includes 'src/**/*.{ts,tsx}'
Note: If you run the above command it will fail, because you won't have
schema.gql
in local.
Ensure you have schema.gql
. Your GraphQL server should have the feature to emit your GraphQL schema to a file.
After the command, you will see a output file including code like this:
// __generated__/GetExchangeRates.ts
export interface GetExchangeRates_rate {
currency: string
rate: number
}
export interface GetExchangeRates {
rates: GetExchangeRates_rate[]
}
So we can replace the last code with the generated types:
import { useQuery, gql } from "@apollo/client"
import { GetExchangeRates } from "./__generated__/GetExchangeRates"
const EXCHANGE_RATES = gql`
query GetExchangeRates {
rates(currency: "USD") {
currency
rate
}
}
`
function ExchangeRates() {
const { loading, error, data } = useQuery<GetExchangeRates>(EXCHANGE_RATES)
if (loading) return <p>Loading...</p>
if (error) return <p>Error :(</p>
return data.rates.map(({ currency, rate }) => (
<div key={currency}>
<p>
{currency}: {rate}
</p>
</div>
))
}
This is much easier!
The downside is that we should run the command to generate type definitions every time we edit GraphQL code, but it is far easier than manual typing.
I think it is enough for smaller projects. But if the project grows, there will be a problem - type reusability.
Step 4 - Reuse type definitions
Thanks to apollo
, we can generate type definitions. However, how to reuse these type definitions?
Imagine we want to separate our component like this:
// ExchangeRates.tsx
import { useQuery, gql } from "@apollo/client"
import { GetExchangeRates } from "./__generated__/GetExchangeRates"
import { ExchangeRateItem } from "./ExchangeRateItem"
const EXCHANGE_RATES = gql`
query GetExchangeRates {
rates(currency: "USD") {
currency
rate
}
}
`
function ExchangeRates() {
const { loading, error, data } = useQuery<GetExchangeRates>(EXCHANGE_RATES)
if (loading) return <p>Loading...</p>
if (error) return <p>Error :(</p>
return data.rates.map((rate) => (
<ExchangeRateItem rate={rate} key={rate.currency} />
))
}
// ExchangeRateItem.tsx
import { GetExchangeRates_rate } from "./__generated__/GetExchangeRates"
interface ExchangeRateItemProps {
rate: GetExchangeRates_rate
}
export function ExchangeRateItem({ rate }: ExchangeRateItemProps) {
const { currency, rate } = rate
return (
<div>
<p>
{currency}: {rate}
</p>
</div>
)
}
As you can see, we can import common GraphQL type definitions from generated code. However, it should become messy because:
- The child component relies on parent's component query.
- Hard to re-use
ExchangeRateItem
because of tied couple of a specific query. - Dependency flow is not linear;
ExchangeRateItem
->__generated__
->ExchangeRates
->ExchangeRateItem
Note: Technically
__generated__
does not depends onExchangeRates
, but conceptually it depends, as type definitions are generated from it.
I haven't fully figured out how to handle this, but have two solutions for it using Fragment
.
Step 4.1 - Create common Query and Fragment
The first one is based on Domain Separation. The idea is to create common GraphQL related files and write logic there instead of components:
// graphql/Rate.ts
import { useQuery, gql } from "@apollo/client"
import {
GetExchangeRates,
GetExchangeRates_rate,
} from "./__generated__/GetExchangeRates"
// Re-export fragment type because of reusability
export type { RateFragment } from "./ExchangeRateItem"
const RATE_FRAGMENT = gql`
fragment RateFragment on Rate {
currency
rate
# ...And other props in the future
}
`
const EXCHANGE_RATES = gql`
query GetExchangeRates {
rates(currency: "USD") {
...RateFragment
}
}
${RATE_FRAGMENT}
`
export const useRates = () => useQuery<GetExchangeRates>(EXCHANGE_RATES)
// Other fragments, hooks, queries will follow
// ExchangeRates.tsx
import { useRates } from "./graphql/Rate"
import { ExchangeRateItem } from "./ExchangeRateItem"
function ExchangeRates() {
const { loading, error, data } = useRates()
if (loading) return <p>Loading...</p>
if (error) return <p>Error :(</p>
return data.rates.map((rate) => (
<ExchangeRateItem rate={rate} key={rate.currency} />
))
}
// ExchangeRateItem.tsx
import { RateFragment } from "./graphql/Rate"
interface ExchangeRateItemProps {
rate: RateFragment
}
export function ExchangeRateItem({ rate }: ExchangeRateItemProps) {
const { currency, rate } = rate
return (
<div>
<p>
{currency}: {rate}
</p>
</div>
)
}
Since we move GraphQL code to ./graphql/Rate
, the dependency became linear again;
-
ExchangeRates
->graphql/Rate
->__generated__
-
ExchangeRates
->ExchangeRateItem
->graphql/Rate
->__generated__
Using Fragment, code for GraphQL became a little longer and verbose. However, it has a benefit of Separation of Concerns.
-
graphql/Rate
knows how to fetch data. -
graphql/Rate
exposes its interface. -
ExchangeRates
andExchangeRateItem
don't know how to fetch data. They don't depend on implementation but interface of data source and type.
And the code on our components become smaller, which is also great for frontend devs.
Step 4.2 - Colocated Fragments
Another solution is to use a pattern called "Colocated Fragments" where child components declare which data is needed.
// ExchangeRates.tsx
import { useQuery, gql } from "@apollo/client"
import { ExchangeRateItem, RATE_ITEM_FRAGMENT } from "./ExchangeRateItem"
const EXCHANGE_RATES = gql`
query GetExchangeRates {
rates(currency: "USD") {
...RateItemFragment
}
}
${RATE_ITEM_FRAGMENT}
`
function ExchangeRates() {
const { loading, error, data } = useQuery<GetExchangeRates>(EXCHANGE_RATES)
if (loading) return <p>Loading...</p>
if (error) return <p>Error :(</p>
return data.rates.map((rate) => (
<ExchangeRateItem rate={rate} key={rate.currency} />
))
}
// ExchangeRateItem.tsx
import { gql } from "@apollo/client"
import { RateItemFragment } from "./__generated__/RateItemFragment"
export const RATE_ITEM_FRAGMENT = gql`
fragment RateItemFragment on Rate {
currency
rate
# ...And other props in the future
}
`
interface ExchangeRateItemProps {
rate: RateItemFragment
}
export function ExchangeRateItem({ rate }: ExchangeRateItemProps) {
const { currency, rate } = rate
return (
<div>
<p>
{currency}: {rate}
</p>
</div>
)
}
In that way, we achieve:
- We don't have to separate GraphQL code form components which needs it
- We don't have to update fields manually when required data changes
- Easy to read code
For more details, please visit: https://www.apollographql.com/docs/react/data/fragments/#colocating-fragments
Codegen tools other than Apollo
TypedDocumentNode
@urigo
recommended TypedDocumentNode
. I have never tried the library, but he is one of the smartest GraphQL developer so you should check it out!
https://the-guild.dev/blog/typed-document-node
@graphql-codegen/cli
This is made by the CTO of The Guild, and widely used. I haven't tried it in my project yet, but it covers almost all of major tools.
https://github.com/dotansimha/graphql-code-generator
Conclusion
- Use
apollo-tooling
or other tools to type GraphQL result - Separate GraphQL related code into a directory (if you think your project is large)
- Use
Fragment
to create common reusable type
If you have any thoughts, please post a comment!
Top comments (4)
Great article, thank you so much!
I would also add a last and final step to make it even cleaner - use generated TypedDocumentNode!
Here is now: the-guild.dev/blog/typed-document-...
Thank you for your comment, Urigo!
I saw the blog and TypedDocumentNode is impressive. Thanks!!
I guess you left off the server side stuff. I personally prefer to work with nest js and graphql as nest js automatically generates all the types for me.
Thanks for your comment. As you mentioned this article is totally about frontend. Nestjs looks great whereas I use type-graphql for my life now.