The "uninitialized constant" error in Ruby on Rails usually occurs when Rails cannot find a constant (e.g., class, module, or constant variable) that you are trying to reference in your code. This error can happen for various reasons, and it's essential to identify the root cause.

Here are some common causes of the "uninitialized constant" error in ActiveAdmin:

  1. Missing Required File or Library: Make sure you have required or included the necessary files or libraries that define the constant you are referencing. For example, if you are using a custom class or module in ActiveAdmin, ensure that the corresponding file is loaded correctly.

  2. Namespacing Issues: Check if the constant you are trying to reference is within the correct namespace. In Ruby on Rails, classes and modules are often defined within specific namespaces. Make sure you are using the correct namespace when referencing the constant.

  3. Typo or Misspelling: Double-check the spelling and capitalization of the constant you are trying to reference. A simple typo can lead to an "uninitialized constant" error.

  4. Autoloading or Autoload Paths: Rails uses autoloading to automatically load classes and modules when they are referenced for the first time. If your constant is not being loaded automatically, check the autoload paths or configure explicit autoloading if necessary.

  5. Load Order or Dependencies: If you have defined the constant in a custom file, ensure that the file is loaded before you reference the constant. Check for load order issues, especially if you have dependencies between different files.

  6. Namespaces in ActiveAdmin: If you are working with ActiveAdmin resources, make sure you are defining them within the correct namespace. ActiveAdmin uses a separate namespace for its resources, and you should define them in the app/admin directory.

For example, if you have a resource named Book in ActiveAdmin, make sure it is defined within the app/admin directory in a file like app/admin/books.rb.

If you provide more specific information about the context in which the "uninitialized constant" error occurs (e.g., the code snippet or file where the error is raised), it would be easier to provide a more targeted solution.

Additionally, you can check the Rails development log or console for any additional error messages or stack traces that might give more insights into the cause of the error. If needed, you can also share relevant code snippets or files to help diagnose the issue more accurately.

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