Some models call for this kind of data. An attribute that can have only one of a few different values. And that set of values almost never changes. You could stuff them in a yaml file, but now you have to look in a totally different place to figure out what your object can do.
When you define an enum, order matters. So if you go back to your code and decide that those values should really be in alphabetical order:. You can get around this by telling enum which number goes with which value:. A bigger problem is what to do outside the Rails world.Rails: Generating Enum Hash Filter
So someone looking at your raw data will have no idea what those numbers mean. This also means that every app that reads that database will have to know that enum mapping. You could dump your enum mapping to the database or a yaml file if you really needed other people to see them.
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You should get an email from me in a few minutes with your free sample chapter. You can learn a little bit more about Ruby each day -- I share the best Ruby and Rails articles I read. And it's great for short conversations and answering questions about software development. A few values, in the model ActiveRecord enums are pretty easy. Pushing through tutorials, and still not learning anything?
Enums with Rails & ActiveRecord: an improved way
Is there any way to using enum on array column like arrtibute supporting array: true? Rails' enum api maps attributes to a single integer column. If you wanted, you could create your own bit mask to support multiple attributes like is often done with user roles.
I think what you're looking for is the attributes api and you could even implement a custom ActiveRecord::Type to handle validation. First, there is no array: true option on the enum method, just leave it out. Last but not least, I'd recommend using a string or Postgres enum type instead of integer columns. Integer columns are problematic because for one, to read it, one needs the source code of the application that wrote the record the version at the time of insertion and second it is unnecessarily hard to remove or replace values.
Learn more. Asked 3 years, 6 months ago. Active 1 year, 6 months ago. Viewed 2k times. EDIT I would like to see that the following test case passes, but actually it fails.
Minitest::Test This connection will do for database-independent bug reports. Did you find a solution to this? Active Oldest Votes.
Since this question is still without answer, this is how it can be done: First, there is no array: true option on the enum method, just leave it out. Your code does not work. Please see my edit on the question. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name.
Email Required, but never shown. The Overflow Blog. Podcast is Scrum making you a worse engineer? The Overflow Goodwill hunting. Upcoming Events. Featured on Meta. Feedback post: New moderator reinstatement and appeal process revisions.Getting value of integer stored in database for enum attribute on Rails ActiveRecord models can get tedious.
This article will help understand how to fetch integer value of enum on ActiveRecord model in Rails. When we fetch any record from database, the column with enum defined over them, will be type casted to their corresponding value on read. As we can see, the status attribute on product already has string value. This will output raw value read from a database row. This will not have any impact of typecasting and deserialization performed by Rails on ActiveRecord object.
Stay up to date! Rails had introduced enums on ActiveRecord models. Fetch string value of enum field When we fetch any record from database, the column with enum defined over them, will be type casted to their corresponding value on read.
Fetch integer value of enum field Sometimes, we need the original value stored in database for such fields for some processing. There are a couple of ways to fetch integer value of enum field. Ruby in Rails. Share this.
Subscribe to Ruby in Rails Stay up to date!By using this website you agree to our terms of service. When your project starts you probably design ERD diagram or a similar one. That process helps to understand the specific domain and mirrors the reality.
Entities that you model contain many attributes of various types. A quite popular requirement is to create an attribute that can be assigned to one of a few available values. In programming, that type is called enumeration or just enum. Rails supports enums from version 4. In our recent project, we worked on a system related to artworks. Artworks were collected into Catalogs. The catalog was one of the biggest models in our app.
Among many attributes, we had 4 of the enum type. Adding enum to an existing model is a really simple task. First of all, you need to create an appropriate migration. Notice that column type is set to integer and this is how Rails keeps enums values in the database. From now you can take advantage of the whole bunch of extra methods. To see all provided methods check ActiveRecord::Enum. This simple solution is great for a start, but you may run into some troubles when your project will grow.
To be prepared, you can implement a few improvements making your enums easier to maintain:. Vulnerability before change: Mapping between declared values and integers kept in the database is based on order in the array. That approach is not flexible at all. Imagine that requirements just have changed. In that case, you should remove old value and add two new ones. To avoid this situation you should declare your enum as a Hash. There is not much to do:.
Working with attributes representing by integers in the database can be annoying. Imagine that you want to query something in rails console or even you need to create a scope based on your enum field. So we can write a where clause like this:. In that case, you need to put an extra effort to make these integers meaningful again.
Another annoying situation can take place when you work with a legacy database like this. You have access to the database and you are interested only in the data kept there. You are not able to get immediate information from what you see. Always need to map these numbers into real values from the domain. To convince you even more, there is also safety point. When declaring ActiveRecord::Enum there is no guarantee that your data will be restricted only to provided values.
In order to persist the status value to the database, we need to generate a migration using the following command:. It's important to mention that, for this case, the column needs to be an integerand it will contain values from 0 to 2.
Setting the default as 0 is a good practice. Those values will mean the following:. Yes, you noticed it right, the order we define the values on our enum does matter a lot. And if we decide to add new values, the recommendation is to add them at the end, so we don't mess with data that we may already have in our database. There is a way for us to override the integer number that will be used to represent a value from our enumyou can use the following approach:.
Cool, enough with the "mappings", let's talk about the convenience methods that we get when using the enumassuming we have the following enum declaration :. Be aware that! Thanks to? Besides the convenience methods and scopes that I already mentioned to you, the main advantage of using enums is that, out of the box, we get validations for the possible values that a column can have. One of the downsides of using an integer column for storing a representation of a string value, like the case of a status column, is that we are going to make it harder for people looking directly at the database table's rows to know what number represents which status.
In the previous examples, there are 3 possible statuses, but we can many more, there is no limit. Instead of using an integer column, you can use a string one.
Your migration should look like this:. That's it, know your posts table will have a string status column and consequently, any person looking at it will know what status the Post has. Now that you have already solved the readability issue in your posts table. There is still one important issue that we need to resolve. The integrity of the information within your database.
As you may recall, validations are handled within your Rails application context. If we are already using enum on Rails, is because we know the values that your status column can have is finite. Let's add the very same constraints we have on our Rails app, to the database. To do so, native databases enums come to our rescue! Interesting, uh? We are using MySQL's enum type to declare the possible values that the status column should have.
You're guessing right, those values should be exactly the same than the ones declared on your Model. PostgreSQL also supports enumsbut we should define them first. We will get a column on the database that will only accept the declared values. That's the same constraint we have on our Rails app, yay! As you can see, there is nothing that indicates that your status column is an enum. Really bad, uh?
Problem solved! It will contain the most reliable dump of your database's structure.Declare an enum attribute where the values map to integers in the database, but can be queried by name.
Scopes based on the allowed values of the enum field will be provided as well. With the above example:. Finally, it's also possible to explicitly map the relation between attribute and database integer with a hash:. Note that when an array is used, the implicit mapping from the values to database integers is derived from the order the values appear in the array.
In the example, :active is mapped to 0 as it's the first element, and :archived is mapped to 1.
In general, the i -th element is mapped to i-1 in the database. Therefore, once a value is added to the enum array, its position in the array must be maintained, and new values should only be added to the end of the array.
To remove unused values, the explicit hash syntax should be used. In rare circumstances you might need to access the mapping directly.
Ruby on Rails - How to Create Perfect Enum in 5 Steps
The mappings are exposed through a class method with the pluralized attribute name, which return the mapping in a HashWithIndifferentAccess :. Use that class method when you need to know the ordinal value of an enum. For example, you can use that when manually building SQL strings:.
It is also possible to supply a custom value:. Source: show on GitHub. Ruby on Rails 5. With the above example: Conversation. The mappings are exposed through a class method with the pluralized attribute name, which return the mapping in a HashWithIndifferentAccess : Conversation.
For example, you can use that when manually building SQL strings: Conversation.Posted by: admin November 26, Leave a comment.
Symbols are appropriate when you want to enhance readability without littering code with literal strings. Constants are appropriate when you have an underlying value that is important. Just declare a module to hold your constants and then declare the constants within that.
Symbols also perform very well. Comparing two symbols for equality, for example, is much faster than comparing two strings. This is my approach to enums in Ruby. I was going for short and sweet, not necessarily the the most C-like. Any thoughts? I wanted an easy way to see what the number represents, easy comparison, and most of all ActiveRecord support for lookup using the column representing the enum. Someone went ahead and wrote a ruby gem called Renum. You can do this by using fetch rather than  :.
Recently we released a gem that implements Enums in Ruby. In my post you will find the answers on your questions. Also I described there why our implementation is better than existing ones actually there are many implementations of this feature in Ruby yet as gems.
It all depends how you use Java or C enums. Symbols is the ruby way. However, sometimes one need to talk to some C code or something or Java that expose some enum for various things. This seems a bit superfluous, but this is a methodology that I have used a few times, especially where I am integrating with xml or some such. This to me serves the purpose of enum and keeps it very extensible too. You can add more methods to the Enum class and viola get them for free in all the defined enums.
Another approach is to use a Ruby class with a hash containing names and values as described in the following RubyFleebie blog post. This allows you to convert easily between values and constants especially if you add a class method to lookup the name for a given value. Another way to mimic an enum with consistent equality handling shamelessly adopted from Dave Thomas. Allows open enums much like symbols and closed predefined enums. December 31, Ruby Leave a comment.
Why am I getting this and how can I get around it?