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So starting off this morning is Bryan Helmkamp. Did I pronounce that right?
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All right, so Bryan. A couple of high points. Bryan currently runs a company called Code Climate. How many people are familiar with Code Climate? Okay, if you're not, check it out.
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It's a great product. I started using it after RubyConf, after he showed me the demo at RubyConf. We started using it for our teams for the projects that we have.
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In addition to Code Climate, Bryan is also heavily involved and is one of the lead organizers for Goru. I got clearance from him before using his Wi-Fi.
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For those of you who aren't aware, Goru is a conference that takes place in New York City. It's a similar single-day, single-track conference. It's well worth the trip and a great excuse to go to New York.
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Oh, one more thing I wanted to mention is that Bryan is also a Ruby Hero as of 2009. If you're not familiar with the Ruby Heroes program, Google it and check it out.
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It's a community effort where we recognize about half a dozen members of the community each year for their extensive contributions to what we do and to help grow the community.
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With that, I'm going to turn it over to Bryan for a discussion that is not about Enterprise Rails, if you saw that on the schedule.
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Refresh your schedule; this morning we're talking about refactoring ActiveRecord.
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Is this mic on? Can people hear me? Okay, cool. Thank you, Kobe. That was a very nice introduction.
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I'd like to begin with a little bit of group therapy. So think back to the last time you were working on a completely greenfield application.
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There was no legacy code, there was no technical debt. You had a test suite that was comprehensive but ran really quickly.
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You had a backlog of features, and you were just in your editor, tearing through them. Can everyone think back to the last time they had that feeling?
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Give me an adjective for how you felt when you were working like that. Just toss one out there.
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Anybody got one? Fun? Productive? Anything else? What's that? Enabled? Yes, great. Sane.
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So, the greenfield feeling is great, right? The problem is that as your requirements increase and you start adding developers to the project, and the requirements start changing, it's kind of like having cows enter your greenfield.
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The problem with letting cows in your greenfield is that after a while they have a tendency to turn a greenfield into a brownfield.
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Then you're sort of in that position where you feel like you're fighting your codebase. Have you ever had that feeling?
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Where it feels like you have to change everything just to get one thing done, and your app is your adversary?
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Then you have to beat it into submission. That's a brownfield.
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So my name is Bryan Helmkamp. I'm the founder of Code Climate. It's a hosted automated service that reviews the Ruby code in your applications.
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Today, I'd like to talk about one particular aspect of this problem as it relates to Rails applications.
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We're going to look at ways to deal with complexity in our model layer and how we might manage that complexity more effectively.
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This is to prevent our greenfields from turning brown.
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As a quick warning, this talk is going to move really fast. I'm going to try to cover seven patterns in one anti-pattern.
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With an intro and an outro in time for questions in about 40 minutes, so if you haven't had coffee yet, God help you.
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I'd like to begin with a quote: Rails makes it natural and easy to build large, well-designed object-oriented systems.
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Do you know who said that? I don't think anybody has ever said that, at least not to me.
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But why is that? I think in that context when someone refers to Rails, they're really referring to the Active Record pattern.
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So we have to go back to what the Active Record pattern is to understand this feeling.
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Active Record was documented in Martin Fowler's book, Patterns of Enterprise Application Architecture.
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If you go back to the source text, he clearly lays out some implications of using the pattern.
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The biggest advantage is simplicity, and we feel this every day when we create a new model and layer on some quick and dirty CRUD sort of behavior.
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We can plug it into forms and perform reads and writes from our database.
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However, Active Records are, by definition, directly coupled to your database schema.
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The problem with this is if you have a small database schema that isn't expanding all the time, and you restrict yourself strictly to the Active Record pattern,
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the tools that you end up with to manage complexity in your domain and in your model layer are very limited.
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If you only have five tables, but you have all sorts of behaviors layered on top of them and only five classes,
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those five classes are going to become pretty problematic pretty quickly.
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Sometimes when people talk about object-oriented systems, they use the term 'ravioli code'.
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This can have a positive or negative connotation depending on who’s speaking or the context.
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However, I'm going to use the positive connotation here: you have these little individual units of code that are loosely coupled.
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They're all sort of sliding around in the same bowl, coordinating together to feed you dinner.
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Rails is calzone code. I believe David Chelimsky coined this phrase.
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If you look at the picture, you can get the feeling for why this fits.
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Your Active Records tend to be these big chunks. If you eat more than two calzones, you're just going to feel really sick.
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Today, we're going to look at ways to turn calzones into ravioli.
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The problem with calzones is that they can grow into God objects.
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If I were to look at your applications today, I would be fairly confident that there are at least two God objects in your application.
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These are probably the user class or account class, whatever you want to call it.
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If you're in any commerce application, I would bet that the user class and the order class are probably the worst code that you've got to deal with.
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You probably dread going in there and making changes because who knows what's going to fly out the other side.
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So how do we solve this? In the past, people have talked about the idea of skinny controllers and fat models.
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They want their controllers to be limited in responsibility to do one thing and one thing well.
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Then offload that responsibility to someone else so the controllers are very easy to understand and you don't feel like you have to fight with them.
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Unfortunately, I think 'skinny controller' as a phrase has done perhaps as much damage as it has done good.
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There's a clear alternative: skinny controllers and skinny models.
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Notice the pluralization on models. There’s no reason we can't have the benefits of well-encapsulated objects with limited responsibilities in our model layer.
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Just like we can have them in our controller layer. On to the patterns.
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There’s going to be a lot of code in the remaining slides. If you can see if you can read the text on the bottom.
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If you can't read that, you should pull up the GitHub repository which will have all the code samples in it.
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It's github.com/codeclimate/refactoring_fat_models. If you don't have a laptop, just maybe you can share over someone's shoulder.
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I want to begin with an anti-pattern. Whenever the topic of refactoring Active Records comes up, one of the first things people want to understand is this idea of extracting mixins.
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When I say mixin, I mean Ruby modules.
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So this would be like if you have a user class that's in a social networking context, and it has a couple of associations and some behaviors around knowing whether it's friends or not.
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In this case, you might include a friending module or a blocking module.
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Here's the problem: I don't really like this. I think that the behavior you get when you include modules is akin to inheritance.
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You're essentially creating complex multiple inheritance hierarchies in your application.
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What's worse is that you've created a junk drawer system.
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If your user class has a thousand lines in it, it's kind of like sweeping those lines under five separate rugs.
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You can't really see it now; it's all split up, but what have you really improved?
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The worst part is, by having your complexity swept under five different rugs, it becomes harder to identify concepts that can be given first-class names.
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I've been saying this for a while: any application with an 'app' concerns directory is concerning.
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Come to find out, Rails 4 generates an 'app concerns' directory by default. I think I'm being trolled.
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So let's go to the actual patterns. The first pattern is value objects.
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Value objects are simple, plain Ruby objects whose equality is dependent on their value and not their identity.
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As such, they're often, but not always, immutable.
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We can look at an example in the Ruby standard library. You've got, in the Kernel, things like Fixnum and Float.
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In the standard library, you have classes like URI and Pathname. Those are all great examples of value objects.
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They layer on nice behaviors.
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In this case, we have a fat ActiveRecord model.
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This one's from Code Climate, and it’s Code Climate's representation of a class in your system.
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We understand information about the classes that you have.
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We might write a road to the database called a constant, which is for your class definition.
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Every class gets a rating from A to F based on a cost that we associate with the class.
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The cost is sort of our estimation of how difficult it would be to fix the smells that we've identified.
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Based on the cost, the rating could be anything from A to F.
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Now, the problem with this code is that the first thing I would notice is that there are three methods that all have a repeated word in the name or arguments.
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That's almost always a telltale sign that you're missing an object.
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When you start having repeated prefixes, suffixes, or words that travel together in method names,
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a rating can't exist on its own.
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The only way to do anything with a rating, like figure out if one rating is higher than another, is to have a constant that has that rating.
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Then ask if the rating is higher than another constant's rating.
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A refactoring that you could take here is to introduce a value object.
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We'll introduce a class which is a Rating and give it a little bit of behavior to start.
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So here, we've added a simple factory method that gives us a nice place to map between costs and the appropriate rating.
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We've also defined the 'to_s' method so that if you put it into a string interpolation, it'll come back out just like you want.
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By using Comparable and the spaceship operator, we now have ratings that can be sorted or compared against one another.
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We can ask a rating what the next worst rating is.
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So if you have a B, you want to get back C, C to D, and on.
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We also have a convenience method for asking if one rating is higher than another.
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By defining the hash and equals methods, we can use ratings as keys in Ruby hashes, and they work just like you would expect.
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This is really useful for Code Climate because we do a lot of operations where we need to group different data by rating.
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We want to show you all of the classes that have a D rating.
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To initialize that, it's very simple.
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You just define a method called 'rating' in your constant and use the factory method to produce the correct rating object.
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If you've seen the ActiveRecord feature called composed_of, it's a macro to basically do the same thing.
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It layers value objects into your models. I think it might be deprecated in part just because it's so simple to do it yourself.
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Never be afraid to add a simple method like this that just returns an object.
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It doesn't even need to return the same instance every time because we've set it up so that if you have two instances of the rating B, they'll always be equal.
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You just create the object, and if the object passes out of scope, it gets garbage collected and everything's fine.
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The implications are we now have value objects that can be made comparable.
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They can be used as hash keys with the 'to_s' method, we can make it easy to interpolate them into strings.
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They also provide a convenient place for factory methods.
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I like to use them whenever you've got an attribute that tends to have logic that hangs around it.
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URL, for example, often need to split out the host from the port.
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Data clumps are a good example if you ever have pieces of data that travel together in your system.
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It doesn't make sense to have one piece without the other, like a street number without a street name.
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That's a good place for a value object.
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If you find yourself using primitives in lots of places and contorting those objects into doing more complex behaviors, that's a good time to look at value objects.
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The second pattern is fairly broad.
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This is the idea of service objects, which are defined as objects that represent standalone operations within your code base.
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They tend to have a short lifecycle, so I like to instantiate new ones and then use them once and throw them away.
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Sometimes they are stateless, but if they're not stateless, that state will go away pretty quickly.
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Let's look at an example. We have a user class that has two different ways that authentication can take place.
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We can authenticate with a password using the BCrypt library. That might be the algorithm that our sessions controller uses.
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We also have a method for token-based authentication, perhaps from an API.
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This method, at the bottom, is necessary, as we need to do a secure compare function when validating the API tokens.
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This ensures we avoid making ourselves vulnerable to timing attacks.
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The problem is that the user class already has to include n different strategies for doing authentication.
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If we wanted to introduce a third way, perhaps with a mobile phone, we're just continuing to expand the responsibility of the user object.
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This secure compare method is right under the token authenticate method in this example.
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However, in real life, that's likely buried at the bottom of your private method definitions, maybe 100 or 200 lines from the public interface.
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It doesn't make sense to say what secure compare means in the context of a user.
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There's a mismatch there. So how could we do it better? We could introduce service objects for the two different authentication strategies.
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A password authenticator could use BCrypt to authenticate users that come in with sessions.
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A token authenticator could securely compare the API tokens with the provided tokens.
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Now, the secure compare function is still a utility function hanging out at the bottom.
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At least the correlation between token authentication and secure string comparison is made much more direct.
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There are no 200 lines of code sitting in between those two things.
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Of course, they're easy to use in the controller.
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We can simply initialize a password authenticator with the required user and then call 'authenticate' on the authenticator.
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Instead of calling a method on the user, what do we get out of this?
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We achieve simpler models—that's what we want. We avoid callback hell, where we have layers of callbacks coordinating across different objects.
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It's hard to know what will happen with them.
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We can also clean up duplication in the controller layer.
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If you've ever had to add an API to an application, you might end up repeating the logic across the API and regular controller versions.
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For example, if there are side effects after someone places an order, you can extract those into a service object.
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That way, you can use it in both controllers.
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When you do so, it has the advantage of making behavior opt-in instead of opt-out.
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Your ActiveRecord model maintains its simplicity for interacting with the database.
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You know what's going to happen, but when you need higher-level behaviors, you can reach for the service objects.
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I like using service objects in this case.
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That was an example of having multiple strategies for doing the same thing.
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If you only have one way to do it and it's particularly complex, you might still want to get it out of the Active Record layer.
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Similarly, coordinate between multiple models which can be a great reason to use service objects.
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Perhaps placing an order involves saving credit card information and managing shipping addresses.
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If you're dealing with external services, you might need to query your payment gateway before allowing an order to go through.
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If you have ancillary concerns, like logic that runs once a month on a cron job, you wouldn't want to give that logic top real estate.
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You can push it over to the side.
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The third pattern is form objects.
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Form objects deal with coordinating multiple models through one form.
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If you've done Rails programming for a while, you know this feeling of dread.
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You get the mockup from your designer, and there are four models on this form. How can we do that?
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Rails has powerful tools for putting applications together very easily, but it doesn't have good solutions for this.
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If you've got a form object, you're probably going to be using that in a create or update flow.
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That's when you're most often dealing with multiple models in a single operation.
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I like to make my form objects quack like Active Record objects. We'll see how that works.
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Here's an example: I've seen this sort of thing before.
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This user class has been extended to support sign-ups that require a username, email address, and company name—all on the same form.
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When the form is submitted, we create both a company record and a user record.
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The person added an accessor to the user for the company name and a before_create callback to create the company.
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This is done before the user is created and assigns the association.
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Have you guys ever seen code like this? It's a little bit hairy and has a few problems.
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If the user save fails after creating the company, it's unclear what state your database will be left in.
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You have to start thinking about when, like, is there a transaction here? What's going to be sent when and when's it going to be rolled back?
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The company method is what I call a shape-shifter method.
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Sometimes it returns a company, and sometimes it returns a string.
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If you just want to create a user but not a company, it's not clear how you would do that.
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Let's refactor it. We're going to introduce a form object called a signup.
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When I'm doing form objects, I like to use the Virtus library; it's lightweight.
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It extends a plain Ruby object with attribute-like behavior.
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So we can declare attributes such as name, email, and company name.
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We can also expose an accessor for the user and the company, which will come in handy.
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Next, we make it quack like an Active Record.
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We define a save method, just like Active Record. If validation succeeds, we proceed to persist.
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The answer is very clearly laid out in the signup class.
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First, we create the company, then create the user hanging off that association.
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We populate instance variables so any coordinating code can access the created user or company.
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Because it's similar to Active Record, the signup controller becomes simple.
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We just instantiate the signup and save it as if it were a model.
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What do we gain? We're layering the concept of aggregation into a single form.
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We've limited the responsibility of our Active Records, which is always a good thing.
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We also have a place to style contextual validation.
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Most of the time, validations on a signup form might change over the life cycle of your business.
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When you have validations that are only relevant to signup, now you have a natural place to put them.
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When to use form objects? Whenever you're aggregating multiple models into a form.
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If you ever see 'accepts_nested_attributes_for,' I hate this method. This is probably my least favorite method in all of Rails.
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It's had all sorts of bugs because it's so complex.
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But you can replace uses of 'accepts_nested_attributes_for' with form objects, and you'll be a lot happier.
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The fourth pattern is query objects.
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Query objects encapsulate a single way to query the database.
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Let's look at an example. This might not be unusual in and of itself, but we have an account imported from an external system.
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We have to run queries to figure out which accounts are ready to be imported.
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Additionally, which accounts have attempted to be imported but the process has failed?
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This requires joins against an imports table.
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The issue here is you're gumming up your ActiveRecord class with a bunch of SQL.
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If you have a bunch of these, you end up pushing down the important behavior of the object.
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What do its instances do? That's the key for objects.
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This gets pushed way down the file, and I understand the benefit of hopping down to SQL for certain types of queries.
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But if I'm scanning through a Ruby file and see big blocks of SQL, it throws me off.
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It begs the question of what is this doing, and why is that there?
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What are better ways to manage that complexity? If you introduce a query object,
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you can define a class that is responsible for executing one query.
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You can initialize it with a relation to gain some benefits.
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Then you move that query out from the top of your ActiveRecord model into its own object.
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You provide a find_each method. If you have a background job that needs to page through accounts to import, you just call that with a block.
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What does this get us? We focus the ActiveRecord on core behavior.
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We get composable objects, which encourages refactoring.
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This theme will recur, but I love first-class objects.
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I don't like class methods; they are difficult to refactor.
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When you get things into an object, your entire OOP toolbox becomes readily available.
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You can do composition, inheritance, and introduce state naturally.
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When would I use this? If I have lots of scopes with subtle variations at the top of my ActiveRecord.
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If I have complicated scopes that take eight lines to run a query, that's a good case for factoring it into a separate object.
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If I have rarely used scopes, something that is a simple scope but is only relevant for an ancillary operation in the domain,
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then maybe it should be in an ancillary file in the codebase.
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The fifth pattern is view objects.
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View objects are what I like to use to refer to objects that back up a template or a partial.
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They might depend on zero, one, or multiple models.
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I've seen all three cases.
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Picture LinkedIn, which likes to give you a percentage completion of your onboarding process.
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LinkedIn also provides a next step; a nice touch, but you don't want to stick that in your user model.
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You might end up with code like this. The problem here? We've got repeated method prefixes.
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The onboarding prefix is evident in two methods. More importantly, you have this non-critical concern in the user class.
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Things you tell users to do are usually hints, not critical logic.
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Instead of putting that logic into the user, we might introduce a view object called onboarding steps.
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You can initialize the onboarding steps object with the user and provide it two methods.
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These methods would return a message for what we should tell the user to do next, and indicate their progress.
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This allows us to remove the prefix and creates a clear mapping between templates and classes.
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We now have a clear place to put any logic that might otherwise mix into templates or helpers.
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What did we accomplish? We achieve simpler templates.
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If you've read about the two-step view pattern, this is kind of an implementation of that.
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If you're not familiar with this pattern, it’s one that is often underused.
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You can avoid excessive use of helpers.
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And again, you can have first-class objects that encourage composition and refactoring.
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You can inherit different view objects from one another, and use one inside of another.
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All of this is difficult if that logic is stuck in an ActiveRecord model.
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Use view objects whenever you have display logic in the model.
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If something is clearly only related to presentation, consider moving it to a view object.
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If it's delivery mechanism-specific, you should do the same.
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For instance, if you can conceptualize the application differently, consider how relevant it still is.
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Whenever you see a partial, if it's doing anything non-trivial and doesn't map one-to-one to an object that can encapsulate that logic,
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consider reaching for a view object.
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The sixth pattern is policy objects.
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Policy objects encapsulate a single business rule, focusing on reads.
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They're about making determinations based on data in your system, not updating that information.
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Everybody has dealt with this problem at one point or another—deciding which email notifications to send.
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In this case, we have about four conditions to consider.
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We need to ensure that emails to the user have not hard bounced.
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We also need to check that the user's preferences allow for them to receive notifications of a given type.
00:30:03.000
If the notification is project-specific, we make sure the user has opted into those notifications.
00:30:09.000
It’s a complex conditional statement.
00:30:15.000
From my perspective, this important domain concept is disguised as a method, floating in a sea of other user object methods.
00:30:23.000
Knowing which emails are sent to which users is critically important in web applications.
00:30:30.000
So, we can promote this into a first-class object, making it easier to answer questions.
00:30:37.000
This way, when a product owner asks what emails we're sending, you now have an object that provides the answer.
00:30:43.000
In this case, we have an email notification policy initialized with a user, notification type, and project.
00:30:50.000
It determines whether an email should be delivered based on Boolean logic.
00:30:57.000
This provides a clean place to extract methods.
00:31:04.000
We could have extracted a method in the user class, but it creates a public interface far removed from the private methods that compose it.
00:31:10.000
This leads to a hodgepodge of private methods at the bottom of your ActiveRecord.
00:31:17.000
Encapsulating a business rule into one object is nice.
00:31:24.000
First-class objects make it easier to build aggregates.
00:31:32.000
Sometimes you have business rules that layer on top of other rules.
00:31:41.000
Authorization is a common case, where you have fine-grained authorization rules built on top of others.
00:31:49.000
Policy objects are great for complicated reads, like our four-branched conditional.
00:31:56.000
For ancillary reads or rules, consider using them.
00:32:03.000
However, if the read is simple and core to the domain, you might not want to extract a policy object.
00:32:10.000
The ActiveRecord pattern shines with simple behaviors.
00:32:15.000
The seventh pattern is decorators.
00:32:23.000
Decorators are about wrapping another object and layering additional behavior.
00:32:30.000
You create an object that responds to either the entire wrapped object's interface or just a segment.
00:32:36.000
For example, we have an order that needs to send email receipts.
00:32:43.000
However, we only want to send email receipts if the order was placed online by a customer.
00:32:50.000
If the order came in over the phone or through fax, we don’t want to send an email.
00:32:57.000
Here, the programmer has added an accessor to the order record called 'placed_online.'
00:33:04.000
They're using this to determine whether to fire the email receipt callback.
00:33:11.000
The problem is 'placed_online' is a hack—it doesn't really make sense as a value to determine sending the email.
00:33:18.000
This callback only fires sometimes, not a core behavior of the object's lifecycle.
00:33:25.000
To resolve this, we can introduce an OrderEmailNotifier, which is a decorator.
00:33:32.000
It's going to wrap the order; we only add logic to the save method.
00:33:39.000
If the order saves successfully, we want to send an email.
00:33:47.000
In the orders controller, which processes orders from customers, we can separate logic for building orders.
00:33:54.000
If we do need to send emails, we layer on relevant logic.
00:34:01.000
We build up the order and its decorators, which means that from the perspective of the create method, it's still an order.
00:34:07.000
We have a nice separation between arrangement and work.
00:34:13.000
This allows us to wire together objects, while maintaining the core behaviors.
00:34:22.000
We've promoted the concept of emailing receipts into a first-class domain object.
00:34:29.000
Additionally, it makes sending email opt-in instead of opt-out.
00:34:36.000
You're never going to accidentally send an email receipt when writing a cron job that just needs to make a small change.
00:34:43.000
I like using this pattern if you have contextual behavior that is only relevant for some orders, depending on how they were placed.
00:34:50.000
If you have behavior that interacts with external web services, you wouldn't want to place that into a callback.
00:34:57.000
If you've put an external service call into an Active Record callback, you know the pain it leads to.
00:35:04.000
Decorators allow you to deal with that concern.
00:35:11.000
Some people prefer to use decorators in the view layer, but I'm focusing on models today.
00:35:18.000
There are gems like Draper designed to make layering additional behavior in the view layer easier.
00:35:25.000
That covers the seven patterns. I want to leave you with one more concept before we move to questions.
00:35:34.000
You have to use your judgment whenever you're applying patterns like this.
00:35:41.000
If you wait too long to introduce good design in your code base, you'll end up in a brownfield.
00:35:48.000
You’ll feel stuck in mud, finding it difficult to get things done.
00:35:55.000
However, you also don't want to over-engineer from the start.
00:36:02.000
Rails allows us to accomplish a lot quickly, but there is conceptual overhead when introducing new patterns.
00:36:10.000
Ideally, your design and architecture will grow incrementally as the complexity of your application increases.
00:36:17.000
It's not a huge step function where you go from no design to perfectly done design.
00:36:25.000
You want to gradually increase as they correlate together.
00:36:32.000
Think about that when applying these patterns to your application. Thank you.
00:36:39.000
Thank you.
