Batching between mesh and a gql handler does not work for mutations

[angelsvirkov]

Describe the bug
We cannot batch mutations between the mesh and a GraphQL Handler.

To Reproduce

Here is an example repository with example code and steps to reproduce - https://github.com/angelsvirkov/graphql-mesh-batch-mutations.

• Codesandbox link: https://codesandbox.io/s/gql-mesh-batch-execute-mutations-467bv

1. Start the apollo gql server with yarn start
2. Open a new terminal and run yarn start-mesh
3. A new browser tab should open the GraphiQL Editor on port 4001
4. Use the following query

mutation Test {
  A: changeName(name: "A")
  B: changeName(name: "B")
  C: changeName(name: "C")
  D: changeName(name: "D")
}

5. Go to the terminal output of the apollo gql server and check the req.body. There are 4 requests instead of 1.

Expected behavior

The apollo gql server, which is a handler of the GQL Mesh, receives 1 request with all mutations inside of it.

Environment:

• OS: macOS (but I think it doesn't matter)
• @graphql-mesh/cli: latest
• @graphql-mesh/graphql: latest
• NodeJS: 12 LTS (but I think it doesn't matter)

Reason why it does not work

The default graphql-js execute function calls executeFieldsSerially which breaks down the concept behind the batch-executor of graphql-tools

https://github.com/graphql/graphql-js/blob/main/src/execution/execute.ts#L379

https://www.graphql-tools.com/docs/batch-execution#batch-the-executor

Additional thoughts:
I am not quite sure if graphql-mesh or graphql-tools is a better place for this issue. I could easily move it if needed it.

Regarding a potential solution. I could not come up with a very simple one. The only thing that comes to me is to somehow fake mutations execution as a query execution, but this is more a workaround than a solution and could have other side effects I am not aware of.

[milindsingh]

Hi @angelsvirkov
Did you find any fix ?

Also, how would we fake mutations execution as a query execution, any suggession?

Thanks