Ability to change Message

I've added a config form for plugging in your custom message. You can find it at /admin/config/allow_only_one/settings.

Apply the patch and let me know if it works fine.

hi #sidharth_soman,
First of all - thank you for your effort and help, much appreciated.

I just tested and everything works as expected.

Thanks for the feedback!

It just occurred to me that it would be more useful to add a menu link under the configuration tab in the toolbar so that the user can access the form through the UI. I'm attaching a patch for it.

Thank you, make sense. And not sure if it is is too difficult to implement but message for bundle would be also fine so there is a different one for other conent types or taxonomies, but not necessary.

I am sorry it has taken me so long to get to reviewing this.

I have a couple concerns after reviewing patch #5

1. The setting link does not appear when on /admin/config
2. The setting link does not appear on the module listing on the /admin/modules page
3. The new setting does not have any support for tokens, so if you opt for custom message, you lose the ability to output a link to the existing content or output the list of fields that are making up check for a duplicate.

Where I would like to see this go is a setting within the field configuration that lets you customize the message that appears before the link and field list

So the default would look like this

There is existing content: {entity title with link} , with identical values for the following field(s): Title {not case sensitive}, Category.

But adding a custom message would look more like this:

A news item with a title and category that you selected already exist. Please alter either the title or the category. Here is the the existing news item that is preventing you from saving yours: {entity title with link} , with identical values for the following field(s): Title {not case sensitive}, Category.

By having the setting ride with the field instance, it would be possible to customize the message for each use.

A nice-to-have would be to have a token for the link to the existing item and a token for the list of fields.