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.
• The Apollo Router doesn't support multipart/form-data uploads.

Uploading files with Apollo Kotlin

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

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apollo {
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  service("service") {
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    mapScalarToUpload("Upload")
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  }
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}

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:

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mutation SingleUpload($file: Upload!) {
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  singleUpload(file: $file) {
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    id
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    path
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    filename
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    mimetype
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  }
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}

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

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

And execute your mutation:

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