fix error indexes

[github0013]

I didn't have enough info. to run rails tests, so I created a repo to test this issue.

Summary

https://github.com/github0013/index_errors/blob/master/spec/models/post_spec.rb#L44-L45
A post has 2 comments.

A. When the first comment has errors, the index is correct (first == 0).
B. When the first comment is valid, but the second is invalid, the error index should be 1; however the index is 0.

Other Information

https://github.com/github0013/index_errors/blob/master/spec/models/post_spec.rb#L62-L66
this checks error child's correct index

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[eugeneius]

There's an existing pull request that does something similar to this: #24728

As I just mentioned there, I think the index is meant to point to the location of the error in the changes that were applied, not the records in the association.

In the test you linked to demonstrate the problem, only one comment has changed, so I believe {:"comments[0].body"=>"can't be blank"} is correct.

[github0013]

I got your point. but.. if so, then I wonder how do we effectively use this indexed Parent.errors? as the other developers are also confused of its usage.

In a case like this one, how do we use the [0] index for the second child error?

[eugeneius]

If you're processing the errors in Rails, you can get them directly from the association:

post.comments.each do |comment|
  if comment.invalid?
    # do something with comment.errors
  end
end

You don't need to look things up with an index; you already have the record.

There isn't much documentation for index_errors, but based on the pull request that originally proposed the feature (#8638) it looks like it's primarily intended to be used when the errors will be sent back to the client.

[github0013]

#8638

See that it is impossible to detect whichEmployment object is error related to.

If this is the main reason why the error messages have indexes now, then I suspect the current indexes are not useful to fulfill the issue #8638 because we still can't indicate which error message is for which child object. (index # mismatched)

By the way, I am also using this method to return JSON data, not to build a HTML form.

[eugeneius]

Okay, here's an example. I make a request to add two comments to a post:

PATCH /posts/1 HTTP/1.0

{ "comments_attributes": [ { "body": "valid body" }, { "body": "" } ] }

With the current implementation, if I serialize post.errors.messages I'll get the following:

{ "errors": { "comments[1].body": ["can't be blank"] } }

I can use the error index to tell that the second comment was invalid.

If we change the indexes to be based on the records in the association, and the post already has three comments, I'll get this instead:

{ "errors": { "comments[4].body": ["can't be blank"] } }

How can I determine which one of the comments I tried to create was invalid?

[sgrif]

Closing in favor of #24728, as it looks to be closer to being mergeable.

[dwieringa]

In my case I have a Rails + Vue.js app. When I save, I was counting on the indexes to tell me which table row has the error. This works great as long as all rows get validated, but in the case where only some rows are validated the indexes point to the "wrong" rows.

I'm actually pushing all of the rows back to Rails via ajax. Rails decides which ones need to be saved/validated, so I'm not sure how I would decipher the indexes upon response.