Type mismatch between variable and argument for optional String / ID

[andyfeller]

In trying to query the GitHub repositoryOwner for retrieving repositories for organizations and/or users, I ran into a problem involving the workaround from https://github.com/shurcooL/githubv4/issues/12 as the interface does not appear to like ID for EndCursor.

When calling this query, the following error is returned from GitHub GraphQL API:

Error: Message: Type mismatch on variable $endCursor and argument after (ID / String), Locations: [{Line:1 Column:101}]

type reposQuery struct {
    RepositoryOwner struct {
        Repositories struct {
            Nodes []struct {
                Name string
            }
            PageInfo struct {
                HasNextPage bool
                EndCursor   string
            }
        } `graphql:"repositories(first: 100, after: $endCursor, ownerAffiliations: [OWNER])"`
    } `graphql:"repositoryOwner(login: $owner)"`
}

func getRepos(owner string, endCursor *string) (*reposQuery, error) {
    query := new(reposQuery)
    variables := map[string]interface{}{
        "owner":     graphql.String(owner),
        "endCursor": endCursor,
    }

    err := client.Query("getRepos", query, variables)

    return query, err
}

In stepping through the code, the error emerges in decoding the response from the server where the query is generated as:

"query getRepos($endCursor:ID$owner:String!){repositoryOwner(login: $owner){repositories(first: 100, after: $endCursor, ownerAffiliations: [OWNER]){nodes{name},pageInfo{hasNextPage,endCursor}}}}"

Any assistance would be greatly appreciated 🙇

[andyfeller]

For reference, this query works with the interface mentioned:

query($owner: String!, $endCursor: String) {
    repositoryOwner(login: $owner) {
        repositories(first: 100, ownerAffiliations: [OWNER], after: $endCursor) {
            pageInfo {
                hasNextPage
                endCursor
            }
            nodes {
                name
                nameWithOwner
            }
        }
    }
}

[dmitshur]

If you look at GitHub's RepositoryOwner interface, the after argument of the repositories field has type String, so that's what needs to be provided. Your code can look something like:

variables := map[string]interface{}{
    "owner":     githubv4.String(owner),
    "endCursor": githubv4.String(endCursor),
}

See here for an example of similar code.

[andyfeller]

Thanks for the follow up, @dmitshur ! That is what I initially did, however because the endpoint wants endCursor to be optional, I had to change it to a pointer. Does that make sense?

[dmitshur]

Yes, if it's an optional GraphQL type, using a Go pointer makes sense. That is also what's done in the code example I linked above. The NewString helper exists for convenience of doing this.

[andyfeller]

So, this is where we're coming full circle as when I'm providing the pointer, GitHub is responding back with the following error:

Error: Message: Type mismatch on variable $endCursor and argument after (ID / String), Locations: [{Line:1 Column:101}]

with the underlying generated query being:

"query getRepos($endCursor:ID$owner:String!){repositoryOwner(login: $owner){repositories(first: 100, after: $endCursor, ownerAffiliations: [OWNER]){nodes{name},pageInfo{hasNextPage,endCursor}}}}"

The only thing I can guess is that the repositoryOwner interface does not like $endCursor:ID with however the variable is being sent over.

[dmitshur]

From what you've shared, I'm fairly confident the problem is with the variables map you're providing to the Query call, specifically this code:

query := new(reposQuery)
variables := map[string]interface{}{
    "owner":     graphql.String(owner),
    "endCursor": endCursor,
}

err := client.Query("getRepos", query, variables)

I think changing it to the following should work:

query := new(reposQuery)
variables := map[string]interface{}{
    "owner":     graphql.String(owner),
    "endCursor": graphql.NewString(graphql.String(endCursor)),
}

err := client.Query("getRepos", query, variables)

If that doesn't help, can you post a complete program that reproduces the issue for you?

Finally, take a look at https://github.com/shurcooL/githubv4#pagination if you haven't already, since that is a functional example for pagination.

[andyfeller]

I'll give it a go! (pun not intended) Seriously: thank you for your amazing patience and help ❤️

[andyfeller]

"endCursor": graphql.NewString(graphql.String(endCursor)),

Unfortunately, this doesn't really solve it especially as it gives compiler errors:

cannot convert endCursor (variable of type *string) to graphql.String compiler InvalidConversion

I've made my repo public and the code is here: https://github.com/andyfeller/gh-dependency-report/blob/initial/cmd/root.go#L294

I'm simply trying to run this as:

go run main.go andyfeller 

[dmitshur]

Ah, that snippet assumed that endCursor was of type string, but in your code its type is *string. In that case, you can just convert it to a *graphql.String directly:

func getRepos(owner string, endCursor *string) (*reposQuery, error) {
    query := new(reposQuery)
    variables := map[string]interface{}{
        "owner":     graphql.String(owner),
        "endCursor": (*graphql.String)(endCursor),
    }

    err := client.Query("getRepos", query, variables)

    return query, err
}

With that change, the program compiles and getRepos makes a successful query with repository names populated. (There are other parts of that program that need modification to run without errors, for example repos = make([]string, 100) creates a slice with 100 empty repository names; it should probably be repos = make([]string, 0, 100) to create an empty slice with 100 capacity.)

[andyfeller]

Thank you again for your patience, @dmitshur 🙇

Would you welcome a PR including a section providing an example of this to avoid confusion from other users?

[andyfeller]

With that change, the program compiles and getRepos makes a successful query with repository names populated. (There are other parts of that program that need modification to run without errors, for example repos = make([]string, 100) creates a slice with 100 empty repository names; it should probably be repos = make([]string, 0, 100) to create an empty slice with 100 capacity.)

😅 thanks for the additional advice; it's been a while since my undergraduate days of only doing C development and this is the 3rd time I've tried teaching myself GoLang.

[dmitshur]

Would you welcome a PR including a section providing an example of this to avoid confusion from other users?

I believe this should be covered by https://github.com/shurcooL/githubv4#pagination; can you please let me know if you think something is missing from there?

I'll close this since I understand the question is resolved.