@lwce/apollo-client
v0.2.0
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Apollo client integration for Lightning Web Components
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@lwce/apollo-client
Apollo GraphQL client for Lightning Web Components
This library is largely inspired from the Apollo React hooks, although because it uses wire-adapters, there are some differences.
This library is currently in an experimental form and may change at any time
Use of wire adapters - Warning
Wire adapters are not yet fully documented in the open source version of LWC because their implementation might change over time. If it feels safe to use wire adapters from a consumer standpoint, the implementors might have to adapt their code when these changes will happen.
Establishing the connection to the GraphQL server
The connection is established through the use of an Apollo client instance. Typically, as GraphQL aims to provide a single endpoint, an application should have one Apollo client created. It is important as such a client is also used to maintain a cache for the data.
If the Apollo client can be passed with each wire adapter through the client
property, the @lwce/apollo-client
library also maintains a global Apollo client instance as a convenience. It can be accessed through its setClient/getClient
functions:
// Register the global Apollo client when the application starts
setClient(new ApolloClient({
uri: 'http://mygraphqlserver.com/graphql'
}));
Running a query
A query can be executed using the useQuery
wire adapter like bellow:
const MYQUERY = gql`
{
books(limit: 5) {
id
title
}
}
`
...
@wire(useQuery, {
query: MYQUERY
}) books;
Because of the current LWC compiler behavior, it is advised to isolate the GraphQL in a constant and then reference this constant. This generates more optimized code, as the LWC will repeat the query several times if not in a constant.
Note: to make the wire adapter react on a variable value change, the whole variables
object has to be replaced, as a change in a property is not detected (even when @track
). For example, changing the offset should be done with code like:
variables = {
offset: 0,
limit: 10
}
@wire(useQuery, {
query: MYQUERY,
variables: '$variables'
}) books;
// Right way to update an object
handleFirst() {
this.variables = {
...this.variables,
offset: 0
}
}
// // This does not trigger a wire adapter change!
// handleFirst() {
// this.variables.offset = 0;
// }
Query Results
The resulting data has the following members:
{
loading, // A boolean that indicates if the query is being loaded
data, // The data returned, can be null or undefined
error, // The data if any, can be null or undefined
initialized, // A boolean that indicates if the query has been executed at least once
client, // The apollo client being used
fetch, // Execute the query with optional variables
}
Note that the wire adapter keeps watching for data changes using the Apollo watchQuery
observable. If it detects changes, then it will update the component appropriately.
Query Options
The options are the one being used by the Apollo client watchQuery(), with a new option:
{
client, // The apollo client instance. If empty, it uses the globally registered one.
lazy, // Indicates that the query should not be executed right away, but later calling fetch()
}
The most notable existing options for the client are:
query
: the GraphQL query to emitvariables
: the list of variables for the query
Refetching the Query
Once initialized, the result provides a fetch(variables)
function that can be used to execute the query again. In case of a lazy
query, it must be called to get the data (the initialized
can be checked to see if it already happened).
Note that the React Hooks library named this function refetch
, but it is named fetch
here for consistency with other LWC projects.
Lazy mode
The GraphQL request is automatically emitted when the wire adapter configuration is available, which means when the component is connected to the DOM. This works well for data needed by the component to display right away, typically a query. But, sometimes, the request should be executed manually. It applies to data requested on demand (list for a pop-up, ...). The fetch
method returns a Promise
that will be resolved when the request is completed. At that time, the @wire
member is updated with the latest data. Note that the Promise is also resolved when the update failed: just access the error member of the @wire
member to check the status.
Here an example of a request executed on demand:
@wire(useQuery, {
query: USERS,
lazy: true
}) users;
readUsers() {
this.users.fetch().then( () => {
// Notification that the data has been updated
// Do something with the @wire data member...
})
}
To support that, the wire adapter offers a lazy
mode. When set to true
, the request is only executed with an explicit call to a fetch()
method, provided as part of the @wire variable.
Executing a mutation
Mutations use the useMutation
wire adapter:
const MY_MUTATION = gql`
mutation updateBook($id: String!, $book: BookInput!) {
updateBook(id: $id, book: $book) {
id
title
}
}
`
...
@wire(useMutation, {
query: MY_MUTATION
}) updateBook;
Similarly to lazy queries, the requests is not executed when the component is initialized but must be executed explicitly. For this, the wire adapter will initialize the result and make available a mutate
method to call:
const variables = {
id,
book: {
title: "new title",
author: "myself,
...
}
};
this.bookCreate.mutate({
variables
});
the mutate
method also returns a promise to enable notification once a mutation has succeeded:
const variables = {
id,
book: {
title: "new title",
author: "myself,
...
}
};
this.bookDelete.mutate({
variables
}).then(() => {
//some notification or alert or variable change
this.showDeleteSuccessAlert = true;
});
Mutation Results
The resulting data has the following members:
{
loading, // A boolean that indicates if the mutation is being executed
data, // The data returned, can be null or undefined
error, // The data if any, can be null or undefined
initialized, // A boolean that indicates if the query has been called once
client, // The apollo client being used
mutate, // The function to call for mutating the data
}
Mutation Options
The options are the one being used by the Apollo client mutate(), with the following options added:
{
client, // The apollo client instance. If empty, it uses the globally registered one.
}
The options are a merge between the global options defined at the @wire
level, and the ones passed to the mutate
method (the later overrides the former).
Error Helpers
Easily convert GraphQL error responses into a human readable string:
import { getErrorString } from '@lwce/apollo-client';
@wire(useQuery, { query: QUERY, lazy: false, variables: '$variables'})
update(response) {
if (response.initialized) {
if (response.error) {
console.error(getErrorString(response.error));
} else {
this.data = response.data;
}
}
}