Query diff error when operation has variables

[lvauvillier]

It seems query diff is not working in some cases when original query use variables.

I have an article container component which retrieve its data and its source from two distinct root queries.

The first time the component is mounted, everything works (the full query is sent to the server). But the second time with a different article and the same source the diff is not working.

Component connection :

export default connect({
  mapQueriesToProps: ({ ownProps }) => ({
    data: {
      query: gql`
        query articleWithSource($articleMid: MID!, $sourceMid: MID!) {
          article: article(mid: $articleMid) {
            rubric
            pubDate
            title
            subtitle
            byline
            abstract
            image {
              url
              width
              height
            }
          }
          source(mid: $sourceMid) {
            name
            image {
              url
              width
              height
            }
          }
        }
      `,
      variables: {
        articleMid: ownProps.params.articleMid,
        sourceMid: ownProps.sourceMid,
      },
    },
  }),
})(withTheme(ArticleContainer));

Generated diff query for the second article :

query articleWithSource($articleMid: MID!, $sourceMid: MID!) {
  article: article(mid: $articleMid) {
    rubric
    pubDate
    title
    subtitle
    byline
    abstract
    image {
      url
      width
      height
    }
  }
}

I get from the server :

{
  "errors": [
    {
      "message": "Variable \"$sourceMid\" is never used in operation \"articleWithSource\".",
      "locations": [
        {
          "line": 1,
          "column": 44
        }
      ]
    }
  ]
}

[stubailo]

Sounds like we might need to avoid sending variables that are not actually included in the query!

[stubailo]

Hmm, this requires additional logic to manipulate the AST to remove variable definitions, scan for what variables are being used, etc.

Would it maybe be better to just get rid of this query diffing feature? Then the only difference is you just put it in as two separate queries if you want them to be cached independently. What do you think? Do you feel like you get a lot of value out of this feature?

[lvauvillier]

I split it in two queries, this is a safe workaround, you're right.
But as it return an unexpected result, i think this is a good idea to disable query diffing for theses queries.