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Uploading files

Apollo Kotlin supports file uploads via the GraphQL multipart request specification with a few caveats:

  • Uploading files with GraphQL is most often suitable for proof-of-concept applications. In production, using purpose-built tools for file uploads may be preferable. Refer to this blog post for the advantages and disadvantages of multiple approaches.
  • The Apollo Router doesn't support multipart-form uploads.

Uploading files with Apollo Kotlin

First, add the following custom mapping to the Apollo Gradle plugin configuration:

apollo {
service("service") {

In this example, the GraphQL defines a custom type named Upload. You can use a different name as needed for your .

Note: You don't need to register a type adapter for Upload, because the mapScalarToUpload method registers it automatically.

Now let's consider a that takes an Upload as a parameter:

mutation SingleUpload($file: Upload!) {
singleUpload(file: $file) {

Create an instance of Upload using one of the factory methods:

// If you're on Android/JVM, you can turn a File into an upload
val upload = File.toUpload("application/json")
// On multiplatform, you can use `DefaultUpload`
val upload = DefaultUpload.Builder()
.content { sink ->
okioSource.use { sink.writeAll(it) }

And execute your :

val response = apolloClient.mutation(SingleUploadMutation(file = upload)).execute()
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