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 possible approaches and their advantages and disadvantages.
• • Neither the Apollo Router Core nor GraphOS Router support multipart/form-data uploads.

Uploading files with Apollo Kotlin

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

1
apollo {
2
  service("service") {
3
    mapScalarToUpload("Upload")
4
  }
5
}

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

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

1
mutation SingleUpload($file: Upload!) {
2
  singleUpload(file: $file) {
3
    id
4
    path
5
    filename
6
    mimetype
7
  }
8
}

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

1
// If you're on Android/JVM, you can turn a File into an upload
2
val upload = File.toUpload("application/json")
3

4
// On multiplatform, you can use `DefaultUpload`
5
val upload = DefaultUpload.Builder()
6
              .fileName("filename.txt")
7
              .content { sink ->
8
                okioSource.use { sink.writeAll(it) }
9
              }
10
              .build()

And execute your mutation:

1
val response = apolloClient.mutation(SingleUploadMutation(file = upload)).execute()