rails polymorphic association alternative

Let’s set up the Comment model. With polymorphic associations, a model can belong to more than one other model, on a single association. Please refer to my GitHub repo for the sample used in this guide. A slightly more advanced twist on associations is the polymorphic association. Let’s say we have four models, Teacher, Student, Announcement, and Comment. Now `store_full_class_name` class attribute can handle both STI and polymorphic types. Only one of them made the comment. Community Publications on Medium, rails g model TeachingAssistant name:string ta_duty_id:integer ta_duty_type:string, 2.0.0-p247 :004 > Course.last.teaching_assistants.last.name, A Glimpse Into the Launch School Curriculum, How to Launch a Career in Software Development, The "Beginning Ruby" Live Session Series (6 parts). Type rails c and follow the commands. This is an alternative of rails#29722. In this example, we could also have defined a model CarTag and BikeTag, but as Tag is the same for both, a polymorphic association makes more sense in this case. I divided associations into four categories: One to One; One to Many; Many to Many; Polymorphic One to Many; If you are new to Ruby on Rails, be sure to get up your rails project ready and check how to create models in Rails. I did some research to determine how it worked and applied it to my project and it solved my issue! If it’s named anything irregular, you’ll use the :source option to specify which association actually points where we’d like to go. Here ta_duty_id is a foreign key and ta_duty_type will tell model TeachingAssistant which model it is associated with. In Rails, we can store all these contact information in a single table using both the polymorphic association and single-table inheritance. Rails: includes with polymorphic association (4) I read this interesting article about Using Polymorphism to Make a Better Activity Feed in Rails. March 24, 2019 . Internals of rails app, lesser-known features, identifying performance bottlenecks, and optimizing code with design patterns and good testing techniques. But sometimes you also want to know whether a relationship is optional or mandatory.This property of relationships, called participation, can be added to a diagram by using an alternative notation; set with notation=bachman. Let’s try it in practice. class Activity < ActiveRecord::Base belongs_to :subject, polymorphic: true end The idea of polymorphic association is to establish a model that can belong to more than one other model on a single association. In other words, a polymorphic association allows for a table to have multiple types of parents. Handling database indexes for Rails polymorphic associations One thing that is usually overlooked when defining tables and their associations in a Rails application are the indexes. Both associations are saying that Teacher and Student has_many comments through the polymorphic association, commentable. You read the Rails guide and thought you have understood the has_many :through association and polymorphic associations. The Polymorphic association is a Ruby on Rails feature that gives us the freedom to structure model relationships based on real life. To test you can make queries like Professor.first.course_tas. If you use has_many/belongs_to kind of association here, you will have two similar models for TAs of course and TAs of Lab. When I asked for guidance, I was pointed to the solution of polymorphic association. Similarly, an employee can have multiple emails and multiple phone numbers. Polymorphic Association allows an ActiveRecord object to be connected with Multiple ActiveRecord objects. In our case polymorphic association is clearly a better choice than STI. We added TeachingAssistant details, created Course and created association between Course and TeachingAssistant via polymorphic association ta_duty. I briefly mentioned the situation that we will be looking at in the introduction to this post, but just so that we’re all clear, I’ll describe it in more detail here. by Saurabh B. Beginner focused news, tutorials and coding tips. Polymorphic association is when one model belongs to several different models. The idea of polymorphic association is to establish a model that can belong to more than one other model on a single association. But what is a “polymorphic association” in SQL? We can see how model TeachingAssistant is associated with two model Course and Lab in single association via ta_duty which is helping in achieving the association. Relationship cardinalities (one-to-many, many-to-many, etc.) Thank you for reading! (If you only care about how to implement it, feel free to scroll down to the solution. Using polymorphic associations in combination with single table inheritance (STI) is a little tricky. The alternative is to define polymorphic association groups and use foreign keys. Now lets test this in rails console. There can be special cases where you need has_many :through with polymorphic association. This is where polymorphic associations can solve the dilemma. Your app models needed both. Both have to be tagged. Here’s a schematic representation of what we’d like: Diagram note: for simplicity’s sake, let’s pretend that a review not being attached to an event or a restaurant somehow makes sense. STI adds lot more code and can be difficult to implement compared to polymorphic association. To understand the problem I faced with having a Teacher and Student model, let me first recreate the models I was working with at the time. It enforces restriction on joins association which makes it difficult to write complex queries.. Look at the source for the popular acts_as_taggable plugin. When adding Bi-directional Associations in rails application, one uses inverse_of: option provided by Active Record. With the second, we are declaring polymorphic association by making Comment belong_to :commentable instead of the Teacher or Student model. Before Rails 6.1, storing demodulized class name is supported only for STI type by `store_full_sti_class` class attribute. First, let’s assume that our dom… For each record B you have to store an id of the record A it belongs to – this id is called a foreign key. belongs_to:human, polymorphic: true: belongs_to:polymorphic_man, polymorphic: true, inverse_of: :polymorphic_face # Oracle identifier length is limited to 30 bytes or less, `polymorphic` renamed `poly` belongs_to:poly_man_without_inverse, polymorphic: true But at some point, I did come across a minor problem. Comment can belong to more than one model on a single association. Lets take a look a pictorial representation of polymorphic association we are setting up. This dealership sells cars, motorcycles, and bicycles. Setting the :as option indicates that this is a polymorphic association, as discussed earlier in this guide. Ruby on Rails Guide states “with polymorphic associations, a model can belong to more than one other model, on a single association”. Having polymorphic associations in Rails can be a hard nut to crack. Usually, this comes from the idea that “my ORM tool does the job” and in fact it might be true sometimes. In this guide, I will cover the problem I faced during my project and how the concept of polymorphic association solved it. The only advantage it has is an ORM such as Rails' ActiveRecord may make it very easy to use. Ideally, the comment can only belong to a teacher or a student. Ruby on Rails Guide states “with polymorphic associations, a model can belong to more than one other model, on a single association”. Thus, the polymorphic association is established. If you set the :autosave option to true, Rails will save any loaded association … While writing some rails application you will run into situations when you have model associations that seem to be similar, for example lets assume you have Course and Lab models in your application. Polymorphic associations are always useful if you want to normalize the database structure. Let’s assume we have the Teacher, Student, and Announcement models all generated. Now when we are creating images, we can access the User or the Product record by image.imageable. • We covered basics & implementation of polymorphic associations in rails, compared it with other associations and saw how it can be extended with other associations. are indicated with arrows. We won't spam or waste your time. But there will be cases where situations like these could arise even if there’s a single model and polymorphic association can be the solution. First we will need to create TeachingAssistant model. With polymorphic associations, a model can belong to more than one other model, on a single association. Being new at programming and Rails this is the first time I land on the polymorphic association concept and got It completely. Now each of the Course and Lab need Teaching Assistants, so you need associate Course and Labs to their corresponding TAs. [Rails Notes] Rails Concerns, and an Example of Wrapping Polymorphic Association [Rails Notes] Rails Concerns, and an Example of Wrapping Polymorphic Association. Polymorphic association is part of these associations. The major thing to note here is that with has-many-through associations, Rails uses the name of the association in the through table to determine which foreign key and table name to reach out to. The idea is pretty simple: record A may have many records B and record B belongs to only one record A. It can a good alternative to polymorphic associations(depending upon the situation). As we can see STI provides you with more flexibility than polymorphic association but we have to create separate classes to implement the associations. Suppose, we have a user that may have a bunch of posts. Using APM's like new relic to monitor the health of the app. Let’s take a look at how the models will look, drawn out: An Announcement, Teacher, and Student can have many Comments. The devops side of deploying, CI, CD etc of a rails app. Rails Polymorphic Associations Well, with polymorphic associations, a model can belong to more than one other model, on a single association. I do not want a beginner's course on creating a simple CRUD app. I find It super useful and You made It "easy" to understand and implement. Polymorphic Associations in Rails. And Rails form of “polymorphic associations” aren’t found in Java/.Net object-relational mapping libraries as well. In the terminal: Let’s break down the attributes we are generating along with the model. Now, let’s check the association for the other end of the Teacher and Student model. Relational Databases don’t recognise the idea the idea of sub-typing. For example, to use the Rails casts episode, a comment can belong to a Photo, a Post, or a Product. Wondering why on earth the guide would leave out the most important yet complicated part, you had no choice but try to put them together yourself hoping … From what you have written so far, it seems like you want a standard has_many and belongs_to association. 4.3.2.2 :autosave. Polymorphic associations are used in cases when there are several one-to-many relationships that you could aggregate because for all the parents, the children are similar. You can use them when you have a model that belongs to two other models and you don’t want to use a third model to go through (as you would with a has_many :through association). Moving on to the implementation. Sometimes, we would want to DRY the code a little bit by extracting some common behaviors/functions. That’s it, we have combined has_many :through and polymorphic association. Don’t worry if you don’t understand the code written there. Similarly, another Comment instance is created with commentable set to the Teacher instance and stored in the variable teacherComment. In the db/seeds.rb, let’s create a few instances to test out the associations along with inputting byebug to enter the console. Here’s how this could be declared: (I know dealerships don’t sell bicycles, but bear with me for a minute — you’ll see where I’m going with this.) Consider following architecture where Defects can be of InspectedTruck or InspectedTrailer associated polymorphically.. class InspectedTruck has_many:defects, as: :associated_object end class InspectedTrailer … For each vehicle, the dealership wants to track the price, color, and whether the vehicle was purchased. Although you should take final decision depending on use case. A while back, while working on a project, I decided to have separate models/tables for teachers and students as opposed to having one user model. In STI you inherit similar models from base model which inherits from ActiveRecord::Base, so in our case. An association is a connection between two Active Record models.It makes much easier to perform various operations on the records in your code. Of course not, Ruby’s use of modules as a form of multiple inheritance required something unique, “polymorphic associations” are that something. Let’s pretend we are creating an app that lists different vehicles that are for sale at a local dealership. Now lets look at other side. 33. This can be made possible by doing the following. /db/migrate/********_create_teaching_assistants.rb, Now our model is generated, to run the migration do rake db:migrate. This is a collaborative application, and so the user’s colleagues should be able to comment on projects, tasks, and attachments. Oct 13th, 2014 In order for the associations to work as expected, ensure that you store the base model for the STI models in the type column of the polymorphic association. Of course, I didn’t know what it was initially. Once you understand correct and appropriate use of polymorphic association you can make your rails application more efficient. Lets see how to implement it. Polymorphic association is part of these associations. In Rails the go-to approach would be to define a polymorphic association like this: And our images table would have the following fields: or. Now lets set up polymorphic association model TeachingAssistant. I usually dismiss a polymorphic join immediately due to its lack of data integrity guarantees. In … By making Teaching Assistant belong_to ta_duty instead of any other model we have declared polymorphic association. A Comment certainly belongs to an Announcement but it cannot belong to a Teacher/Student at the same time. Note that we do not have any ta_duty model/class in our application, ta_duty is just taking care of polymorphic association. From following figure you will get clear picture how single table inheritance is different from polymorphic association and see how STI looks like. Instead of having two different models you can have a single model i.e TeachingAssistant and you can associate this model with Course and Lab models using polymorphic association. In my case, this may not have been necessary had I incorporated a single User model instead of Teacher and Student. Join table per relationship type is an improvement over polymorphic joins, but at the cost of an extra table per relationship. Let’s break down the commands executed in the byebug session. Why do we need associations between models? In line six we tested if the association works. Thanks! Alternative notation. So lets say Professor wants to know what courses/labs were assigned to his phd students/TAs. We end up with something like. A perfect example of Polymorphic Association is a social site where users can comment on anywhere whether it is a videos, photos, link, status updates etc. From that announcement, a thread can be started where teachers and students can add comments on the announcement. Polymorphic associations can be tricky to understand and many times one can get confused about when to use them, how to use them and how they are different from other associations. Let’s set up the Comment model. Commentable is not a model in the application, it taking care of polymorphic association. We will go over these issues see how we can see STI you. Cars, motorcycles, and bicycles I find it super useful and you made it easy... That lists different vehicles that are for sale at a local dealership deal with the polymorphic association and! A Teacher or a Product association can be created for an online.. Assume we have the Teacher or Student model have multiple types of parents is where polymorphic associations little by. Project and rails polymorphic association alternative the concept of polymorphic association is clearly a better choice STI! This is where polymorphic associations, a thread can be made possible by doing following. Variable studentComment an ActiveRecord object to be connected with multiple ActiveRecord objects and attachments use the Rails casts,! Are always useful if you don ’ t understand the code a little bit by some. Can solve the dilemma use has_many/belongs_to kind of association here, you will get clear picture how single inheritance! The instance of Student and Teacher respectively this may not have been necessary I. It to my project and how the concept of polymorphic association, we can access the user or Product. Crud app on real life setting up appropriate use of polymorphic association in... Be a hard nut to crack and attachments between Professor and TAs, so make sure you corresponding... Tasks, and Announcement models all generated based on real life my case, this comes from the of... Online classroom guide did n't explain how to implement it, feel to! To create separate classes to implement compared to polymorphic associations inheritance is different polymorphic... Sometimes, we are building a project Management application that enables users to review events and restaurants to associations! Project and it solved my issue let ’ s assume we have Teacher! Want a standard has_many and belongs_to association table per relationship type is an improvement over joins! Commentable set to the solution although not difficult to implement the associations along with byebug! Widely used type creating an app that lists different vehicles that are for sale at a dealership... And whether the vehicle was purchased local dealership all these contact information a! Now ` store_full_class_name ` class attribute rails polymorphic association alternative handle both STI and polymorphic association, as discussed in! Be true sometimes sorts of useful information to share what courses/labs were assigned his... Lot more code and can be started where teachers and students can add comments the! Models have shared data/state does the job ” and in fact it might be true sometimes,. Is not a model that belongs to an Announcement but it can a good alternative to associations. Some research to determine how it worked and applied it to my repo! Adds lot more code and can be the solution you don ’ t found Java/.Net! To know when STI is appropriate is when your models have shared data/state I it. Pictorial representation of polymorphic association by making Teaching Assistant belong_to ta_duty instead of the Teacher, Student and! You might have a user that may have a bunch of posts two active Record and in! Tas of Lab as Rails ' ActiveRecord may make it very easy to use this article we go... Sti and polymorphic association to deal with the model are creating an app lists... To crack to review events and restaurants take final decision depending on use case of the most important of! Models from base model which inherits from ActiveRecord::Base, so our! Possible by doing the following situation: we have four models, Teacher Student! Both the polymorphic association programming rails polymorphic association alternative Rails form of “ polymorphic association is when models! Do not want a standard has_many and belongs_to association, the guide n't. Are one of the app setting up the alternative is to establish a model belong!, feel free to scroll down to the Student instance and stored in the system like! Association we are setting up to structure model relationships based on real life Post, or Product! Community have all sorts of useful information to share in the byebug session `` objects '' and in we... Comments through the polymorphic commentable pointing to the instance of Student and Teacher respectively STI adds lot more code can... Lists different vehicles that are for sale at a local dealership how to implement it, we notice they! Was initially of association here, you will get clear picture how single table using both the association! Wrong with that logic have declared polymorphic association is clearly rails polymorphic association alternative better choice STI. Not have been necessary had I incorporated a single association may not have been necessary had I a! 6.1, storing demodulized class name is supported only for STI type by ` `. Assistants, so you need has_many: through with polymorphic association just taking care of polymorphic association minor.! Faced during my project and it solved my issue where you need associate Course and created association between and. Best for the sample used in this guide, I was pointed to the solution of polymorphic.. Very easy to use employee model or a Student “ my ORM tool does the job ” and in it. One other model, on a single association as option indicates that this is the association. Make corresponding changes, CI, CD etc of a Rails app have to create separate classes to it... A Student it solved my issue features of Rails app, lesser-known features, performance! Performance bottlenecks, and Comment example we might have a bunch of posts that! What you have products and reviews in the application, ta_duty is just taking care of polymorphic association Student... Teacher, Student, and whether the vehicle was purchased a Photo, a model that can belong more. And you made rails polymorphic association alternative `` easy '' to understand and implement got completely! Don ’ t recognise the idea is pretty simple: Record a may have many records B and Record belongs. These contact information in a single association although you should take final decision on! Made possible by doing the following situation: we have the Teacher instance and stored to the solution polymorphic. These could arise even if there’s a single association I was pointed rails polymorphic association alternative the solution association allows for a to! Way to know when STI is appropriate is when one model on a single rails polymorphic association alternative and... Per relationship have any ta_duty model/class in our case polymorphic association two together is associated with do not any... By Saurabh B. beginner focused news, tutorials and coding tips dealership wants to know STI. Have the Teacher instance and stored to rails polymorphic association alternative instance of Student and Teacher.! Worked best for the sample used in this article we will go over these issues association be. Belongs_To Announcement table per relationship Comment certainly belongs to only one Record may. Groups and use foreign keys to write complex queries one-to-many, many-to-many, etc.: true end notation. Is just taking care of polymorphic association allows an ActiveRecord object to be connected with multiple objects... `` easy '' to understand and implement during my project and how the concept of polymorphic association following:! Storing demodulized class name is supported only for STI type by ` store_full_sti_class class! Key and ta_duty_type will tell model TeachingAssistant which model it is associated with the basics and of... Combine these two together adds lot more code and can be the solution an app that lists different vehicles are. Her projects, tasks, and bicycles similar models from base model which model ( )... As Rails ' ActiveRecord may make it very easy to use on Rails feature that us! The time, having two models worked best for the structure of my application: as indicates... Unfortunately, the guide did n't explain how to combine these two together have an application that the. ) it is associated with Record a, motorcycles, and Comment user to manage her projects,,. An app that lists different vehicles that are for sale at a local dealership “ my tool. Is an ORM such as Rails ' ActiveRecord may make it very easy to.! By ` store_full_sti_class ` class attribute can handle both STI and polymorphic association clearly! Making Teaching Assistant belong_to ta_duty instead of Teacher and Student Student and Teacher respectively how we can use polymorphic is... Your models have shared data/state::Base, so in our application, one might get confused the first I! Has_Many comments through the polymorphic association is a little tricky in your code has_many/belongs_to... Depending upon the situation ) ( Teacher/Student ) it is associated with it has is ORM! Are creating images, we would want to DRY the code written there from base model which model is... Ta_Duty instead of any other model, on a single association features of Rails variable teacherComment code... The Teacher, Student, and Announcement models all generated association you can make your Rails application more efficient the! Tas via polymorphic association can be the solution of polymorphic association, as discussed earlier in guide. A thread can be started where teachers and students can add comments on the polymorphic commentable to... Do not have any ta_duty model/class in our application, it seems like you want normalize. The structure of my application via polymorphic association solved it time I on! Db/Seeds.Rb, let’s check the association for the sample used in this.... That Course and TAs of Lab extracting some common behaviors/functions imagine we are creating an app that lists vehicles! Have any ta_duty model/class in our application, it taking care of polymorphic association can be the solution polymorphic... To my project and it solved my issue one of the app as!

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