Uploading files

Hot Chocolate implements the GraphQL multipart request specification which allows it to handle file upload streams.

Usage

In order to use file upload streams in our input types or as an argument register the Upload scalar like the following.

services
    .AddGraphQLServer()
    .AddType<UploadType>();

In our resolver or input type we can then use the IFile interface to use the upload scalar.

public class Mutation
{
    public async Task<bool> UploadFileAsync(IFile file)
    {
        using Stream stream = file.OpenReadStream();
        // we can now work with standard stream functionality of .NET
        // to handle the file.
    }

    public async Task<bool> UploadFiles(List<IFile> files)
    {
        // Omitted code for brevity
    }

    public async Task<bool> UploadFileInInput(ExampleInput input)
    {
        // Omitted code for brevity
    }
}

public class ExampleInput
{
    [GraphQLType(typeof(NonNullType<UploadType>))]
    public IFile File { get; set; }
}

Note: The Upload scalar can only be used as an input type and does not work on output types.

Configuration

If we need to upload large files or set custom upload size limits, we can configure those by registering custom FormOptions.

services.Configure<FormOptions>(options =>
{
    // Set the limit to 256 MB
    options.MultipartBodyLengthLimit = 268435456;
});

Based on our WebServer we might need to configure these limits elsewhere as well. Kestrel and IIS are covered in the ASP.NET Core Documentation.

Last updated on 2021-09-24 by Tobias Tengler