Fixing ‘undefined Method’ Errors In Ruby On Rails

[Fixing ‘undefined Method’ Errors In Ruby On Rails]


Executive Summary


This article explores the causes and solutions to the common ‘undefined method’ error in Ruby on Rails applications. It provides a comprehensive understanding of this error and offers practical recommendations to address it. By following the guidance presented here, developers can effectively resolve this issue to ensure their Rails applications function as expected.



The ‘undefined method’ error in Ruby on Rails is a common error that occurs when a method called on an object in a Rails application is not recognized or defined. This error can result from various causes, ranging from typos in method names to incorrect object associations. Resolving this error is crucial for maintaining a stable and functional Rails application.

Subtopics and Solutions

1. Method Name Typo

The leading cause of this error is a misspelling or typo in the method name. When calling a method on an object, always ensure that the method name is entered correctly, including its casing and any special characters. Double-check your method names carefully and correct any errors that may be causing the ‘undefined method’ error.

2. Undefined Associations

Referencing an undefined or incorrect association between objects in your Rails application can also result in this issue. Verify the ActiveRecord relationship definitions for the relevant models to ensure that the association exists and is defined correctly in the model classes. Address any missing or incorrect associations to avoid runtime errors.

3. Adapter-Specific Methods

Some Rails methods are specific to individual database adapters, such as ‘find_or_create_by’ for the PostgreSQL adapter. Trying to use adapter-specific methods with an incorrect or incompatible adapter can cause the ‘undefined method’ error. Ensure that you are using adapter-specific methods that are compatible with the database adapter you are employing in your Rails application.

4. Name Scopes and Dynamic Method Names

Named scopes in Rails allow for specifying custom query methods in your models. However, these scopes must be defined within the scope of the model class to be recognized. Ensure you have correctly defined any named scopes that you are attempting to use within the model class to avoid encountering ‘undefined method’ errors.

5. Private or Protected Methods

In Ruby on Rails, private and protected methods can only be accessed within the same class or inherited classes. If you attempt to access a private or protected method from a different context, you will encounter an ‘undefined method’ error. In such cases, ensure that you are accessing the method from the appropriate scope or consider making the method public if it needs to be accessible from other contexts.


The ‘undefined method’ error in Ruby on Rails applications can be effectively addressed by understanding the underlying causes and implementing appropriate solutions. By carefully examining method names, verifying object associations, using adapter-specific methods correctly, and defining named scopes and accessing scopes and methods within the correct context, developers can resolve ‘undefined method’ errors and maintain a robust and responsive Rails application.

Keyword Phrase Tags

  • Ruby on Rails
  • Undefined Method Error
  • ActiveRecord Associations
  • Adapter-Specific Methods
  • Named Scopes
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Comments 12
  1. This is a great solution if you’re looking to hack your way around the problem, but it’s not the best practice.

  2. I fixed this error once by sacrificing a goat and spinning around three times. But hey, this solution works too.

  3. This error can also be caused by a missing comma in your model definition. Double check your syntax to make sure you have all the necessary commas.

  4. I’m not sure this solution will work for me because I’m using a different version of Rails. Does anyone know if this will still work in Rails 5?

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