"Cannot return null for non-nullable field" error

Parse Server 📡 GraphQL API
1

I have an Item custom class, and I use a custom graphql mutation to update an item via a resolver in Cloud code so that I can do some other middleware things at the same time.

# custom schema.graphql
extend type Mutation {
  editItem(input: UpdateItemInput!): UpdateItemPayload @resolve
}

// graphql playground
mutation {
  editItem(
    input: {
      id: "gKTdECrXci"
      fields: {
	    title: "New title"
      }
    }
  ) {
    item {
      title
    }
  }
}

Invoking the mutation results in this error:
"message": "Cannot return null for non-nullable field UpdateItemPayload.item."

Adding UpdateItemPayload (from Parse’s generated schema) to my custom schema does not change things:

# custom schema.graphql
type UpdateItemPayload {
  # This is the updated object.
  item: Item!
  clientMutationId: String
}

However, if instead I short-circuit things and don’t use UpdateItemPayload at all, my mutation work fine, and the item is updated correctly:

# custom schema.graphql
extend type Mutation {
  editItem(input: UpdateItemInput!): Item! @resolve
}

// graphql playground
mutation {
  editItem(
    input: {
      id: "gKTdECrXci"
      fields: {
	    title: "New title"
      }
    }
  ) {
    title
  }
}

How can I get past this and be able to use UpdateItemPayload? I would like my custom mutation format to match what Parse is using.

2

Could you share the cloud code that you are using to resolve this mutation?

3

Sure…I’ve distilled it down a bit for use here, but it still throws the error.

Parse.Cloud.define('editItem', async (req) => {
  const { params: { input: { id, fields } } } = req;
  const itemQuery = new Parse.Query('Item');
  const item = await itemQuery.get(id);
  return item.save({ ...fields });
});
4

You probably need something like this:

Parse.Cloud.define('editItem', async (req) => {
  const { params: { input: { id, fields } } } = req;
  const itemQuery = new Parse.Query('Item');
  const item = await itemQuery.get(id);
  return { item: item.save({ ...fields }) };
});
5

Copy that! Thank you. I didn’t realize that UpdateItemPayload wouldn’t “build” the data structure to be returned for me on its own.

The actual solution is slightly different because I have to await item.save() so it should be:

return { item: await item.save({ ...fields }) };

Or something with a bit less code smell than dumping an await in the middle of the object. It’s all working now. Thanks again!

6

You do not need to await item save since GraphQL will await it for you normally.

7

Lol, you’re right, of course. Brain fade.