Fix duplicate fields in preloads

[nitin302]

This is a documentation change, where we are looping over Selections Twice, which is causing duplicates. I've removed one nested preload to removed these duplicates.

[vektah]

Thoughts @RichardLindhout ?

[RichardLindhout]

There are cases where this is needed I think with fragments, maybe we need to remove duplicates but there was a case when something was inside fragments we need this. I think this issue was posted here. Maybe this is resolved now with newer versions?

My issue back then:
#954

More on that issue here:
#746

Maybe we could do a function where we only append if not exist yet. I did not see this problem before. Do you have a query which result in duplicates?

I generate type-safe preloads here:
https://github.com/web-ridge/gqlgen-sqlboiler/blob/master/examples/social-network/helpers/preload.go

Latest helpers:
https://github.com/web-ridge/gqlgen-sqlboiler/blob/master/helper/preload.go

[RichardLindhout]

I think if you don't include it, selections won't resolve nested fragment fields. However removing duplicates would be a good idea.

[nitin302]

query Search($input: NewSearch!) {
  search(input: $input) {
    chats {
      id
      lastMessage
      messagestats {
        noOfMessages
      }
    }
  }
}

This returns an array of Chats in a Search Response.

I was seeing duplicates, when I fetched the fields, as shown in documentation. Every nested field was duplicated.

I am not using any fragments, Maybe there no duplicates when using fragments. However, for simple queries, it causes duplicates, maybe you can remove duplicates (or insert in to the array if it is not present array).

[RichardLindhout]

Don't have time to test a.t.m.
@vektah Has something changed in the SelectionSet lately or in the new parser?

Maybe this instead of appending

func appendPreloadIfMissing(preloads []string, preloadToAdd string) []string {
    for _, preload := range preloads {
        if preload == preloadToAdd {
            return slice
        }
    }
    return append(preloads, preloadToAdd)
}

[RichardLindhout]

Field are indeed duplicated but for me only column.Selections returned the right fields for me with fragments. SelectionSet did not

[RichardLindhout]

This should fix it: #1189