Async-graphql: Dataloader mulitple values with the same key can return None

[dhendrie91]

Values with the same key can't be returned more than once from the dataloader. I think this is because the value from the HashMap is removed here https://github.com/async-graphql/async-graphql/blob/master/src/dataloader/mod.rs#L166 ?. This is my first time using a dataloader pattern with GraphQL so unsure if this is expected behaviour or not.

Expected Behavior

When loading data using a dataloader if two values have the same hash key the dataloader will return the same data for values with the same key.

So for example a query like this where multiple users can have the same account (or organisation) should return the same account for all users where their account ID is the same.

query {
  users{
    id 
    accountId
    account {
      id
    }
  }
}

should return

{
  "data": {
    "users": [
      {
        "account": {
          "id": "4ed99ea5-bff8-47ec-91f8-e74b73d5f9d1"
        },
        "accountId": "4ed99ea5-bff8-47ec-91f8-e74b73d5f9d1",
        "id": "19164642-c3ee-48fe-b459-dfcb5544833c"
      },
      {
        "account": {
          "id": "f7496608-99d6-462f-996b-8b21507e60f1"
        },
        "accountId": "f7496608-99d6-462f-996b-8b21507e60f1",
        "id": "05282b7b-1bf2-4774-8b18-edad120f00f4"
      },
      {
        "account": {
          "id": "f7496608-99d6-462f-996b-8b21507e60f1"
        },
          "accountId": "4ed99ea5-bff8-47ec-91f8-e74b73d5f9d1",
          "id": "c6f2f96e-ab06-4381-b12a-15783d26ad25"
      },
      {
        "account":  {
          "id": "f7496608-99d6-462f-996b-8b21507e60f1"
        },
          "accountId": "f7496608-99d6-462f-996b-8b21507e60f1",
          "id": "99fb4448-34ab-44c6-bd2f-96dc026a6f1d"
      },
    ]
  }
}

Actual Behavior

Records with the same key return the correct value once but then return None and the graphql value evaluates to Null.

{
  "data": {
    "users": [

      {
        "account": {
          "id": "4ed99ea5-bff8-47ec-91f8-e74b73d5f9d1"
        },
        "accountId": "4ed99ea5-bff8-47ec-91f8-e74b73d5f9d1",
        "id": "19164642-c3ee-48fe-b459-dfcb5544833c"
      },
      {
        "account": {
          "id": "f7496608-99d6-462f-996b-8b21507e60f1"
        },
        "accountId": "f7496608-99d6-462f-996b-8b21507e60f1",
        "id": "05282b7b-1bf2-4774-8b18-edad120f00f4"
      },
      {
        "account": null,
        "accountId": "4ed99ea5-bff8-47ec-91f8-e74b73d5f9d1",
        "id": "c6f2f96e-ab06-4381-b12a-15783d26ad25"
      },
      {
        "account": null,
        "accountId": "f7496608-99d6-462f-996b-8b21507e60f1",
        "id": "99fb4448-34ab-44c6-bd2f-96dc026a6f1d"
      },
    ]
  }
}

Steps to Reproduce the Problem

My data loader

#[async_trait::async_trait]
impl Loader<Uuid> for AccountLoader {
    type Value = Account;
    type Error = FieldError;

    async fn load(&self, keys: &[Uuid]) -> Result<HashMap<Uuid, Self::Value>, Self::Error> {
        let fetch = sqlx::query_as!(Account, "select id from accounts where id = any($1) ", keys)
            .fetch_all(&*self.shared_pool)
            .await?;

        let accounts = fetch
            .into_iter()
            .map(|account: Account| (account.id, account.clone()))
            .collect();

        Ok(accounts)
    }
}

on Version 2.4.6

[sunli829]

I'm so sorry this is a bug, I fixed it in v2.5.7.

[dhendrie91]

@sunli829 thanks so much, I've tested this on the master branch and confirms it fixes my issue :partying_face: . Thanks for the quick response. While i'm here I just want to say I'm loving async-graphql, its a great library and the docs are brilliant. Keep it up :smile:

[sunli829]

@sunli829 thanks so much, I've tested this on the master branch and confirms it fixes my issue 🥳 . Thanks for the quick response. While i'm here I just want to say I'm loving async-graphql, its a great library and the docs are brilliant. Keep it up 😄

Haha, I am very happy to be able to help you.