393: Is REST the Best? APIs and Domain Modeling

It's updates on the work front today! Stephanie was tasked with removing a six-year-old feature flag from a codebase. Joël's been doing a lot of small database migrations.

A listener question sparked today's main discussion on gerunds' interesting relationship to data modeling.

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• Episode 386: Value Objects Revisited: The Tally Edition
• RailsConf 2017: In Relentless Pursuit of REST by Derek Prior
• REST Turns Humans Into Database Clients
• Parse, don’t validate
• Wikipedia Getting to Philosophy

Transcript:

JOËL: Hello and welcome to another episode of The Bike Shed, a weekly podcast from your friends at thoughtbot about developing great software. I'm Joël Quenneville.

STEPHANIE: And I'm Stephanie Minn. And together, we're here to share a bit of what we've learned along the way.

JOËL: So, Stephanie, what's new in your world?

STEPHANIE: So, this week, I've been tasked with something that I've been finding very fun, which is removing a six-year-old feature flag from the codebase that is still very much in use in the sense that it is actually a mechanism for providing customers access to a feature that had been originally launched as a beta. And that was why the feature flag was introduced.

But in the years since, you know, the business has shifted to a model where you have to pay for those features. And some customers are still hanging on to this beta feature flag that lets them get the features for free. So one of the ways that we're trying to convert those people to be paying for the feature is to, you know, gradually remove the feature flag and maybe, you know, give them a heads up that this is happening.

I'm also getting to improve the codebase with this change as well because it has really been propagating [laughs] in there. There wasn't necessarily a single, I guess, entry point for determining whether customers should get access to this feature through the flag or not. So it ended up being repeated in a bunch of different places because the feature set has grown. And so, now we have to do this check for the flag in several places, like, different pages of the application. And it's been really interesting to see just how this kind of stuff can grow and mutate over several years.

JOËL: So, if I understand correctly, there's kind of two overlapping conditions now around this feature. So you have access to it if you've either paid for the feature or if you were a beta tester.

STEPHANIE: Yeah, exactly. And the interesting thought that I had about this was it actually sounds a lot like the strangler fig pattern, which we've talked about before, where we've now introduced the new source of data that we want to be using moving forward. But we still have this, you know, old limb or branch hanging on that hasn't quite been removed or pruned off [chuckles] yet. So that's what I'm doing now.

And it's nice in the sense that I can trust that we are already sending the correct data that we want to be consuming, and it's just the cleanup part. So, in some ways, we had been in that half-step for several years, and they're now getting to the point where we can finally remove it.

JOËL: I think in kind of true strangler fig pattern, you would probably move all of your users off of that feature flag so that the people that have it active are zero, at which point it is effectively dead code, and then you can remove it.

STEPHANIE: Yeah, that's a great point. And we had considered doing that first, but the thing that we had kind of come away with was that removing all of those customers from that feature flag would probably require a script or, you know, updating the production data. And that seemed a bit riskier actually to us because it wasn't as reversible as a code change.

JOËL: I think you bring up a really interesting point, which is that production data changes, in general, are just scarier than code changes. At least for me, it feels like it's fairly easy generally to revert a code change. Whereas if I've messed up the production database, [laughs] that's going to be unpleasant few days.

STEPHANIE: What's interesting is that this feature flag is not really supported by a nice user interface for managing it. And so, we inevitably had to do a more developer-focused solution to remove these customers from being able to access this feature. And so, the two options, you know, that we had available were to do it through data, like I mentioned, or do it through that code change. And again, I think we evaluated both options. But what's kind of nice about doing it with the code change is that when we eventually get to delete those feature flag records, it will be really nice and easy.

JOËL: That's really exciting. One thing that's different about kind of more mature projects is that we often get to do some kind of change management, unlike a greenfield app where you just get to, oh, let's introduce this new thing, cool. Oftentimes, on a more mature project, before you introduce the new thing, you have to figure out, like, what is the migration path towards that? Is that a kind of work that you enjoy?

STEPHANIE: I think this was definitely an exercise in thinking about how to break this down into steps. So, yeah, that change management process you mentioned, I, like, did find a lot of satisfaction in trying to break it up, you know, especially because I was also thinking that you know, maybe I am not able to see the complete, like, cleanup and removal, and, like, where can someone pick up after me? In some ways, I feel like I was kind of stepping into that migration, you know, six years [laughs] in the making from beta to the paid product.

But I think I will feel really satisfied if I'm able to see this thing through and get to celebrate the success of saying, hey, like, I removed...at this point, it's a few hundred lines of code. [laughs] And also, you know, with the added business value of encouraging more customers to pay for the product. But I think I also I'm maybe figuring out how to accept like, okay, like, how could I, like, step away from this in the middle and be able to feel good that I've left it in a place that someone else could see through?

JOËL: So you mentioned you're taking this over from somebody else, and this has been kind of six years in the making. I'm curious, is the person who introduced this feature flag six years ago are they even still at the company?

STEPHANIE: No, they are not, which I think is pretty typical, you know, it's, like, really common for someone who had all that context about how it came to be. In fact, I actually didn't even realize that the feature flag was the original beta version of the product because that's not what it's called. [laughs] And it was when I was first onboarding onto this project, and I was like, "Hey, like, what is this? Like, why is this still here?" Knowing that the canonical, you know, version that customers were using was the paid version.

And the team was like, "Oh, yeah, like, that's this whole thing that we've been meaning to remove for a long time." So it's really interesting to see the lifecycle, like, as to some of this code a little bit. And sometimes, it can be really frustrating, but this has felt a little more like an archaeology dig a little bit.

JOËL: That sounds like a really interesting project to be on.

STEPHANIE: Yeah. What about you, Joël, what's new in your world?

JOËL: So, on my project, I've been having to do a lot of small database migrations. So I've got a bunch of these little features to do that all involve doing database migrations. They're not building on each other. So I'm just doing them all, like, in different feature branches, and pushing them all up to GitHub to get reviewed, kind of working on them in parallel.

And the problem that happens is that when you switch from one branch where you've run a migration to another and then run migrations again, some local database state persists between the branch switch, which means that when you run the migrations, then this app uses a structure.sql. And the structure.sql has a bunch of extra junk from other branches you've been on that you don't want as part of your diff. And beyond, like, two or three branches, this becomes an absolute mess.

STEPHANIE: Oh, I have been there. [laughs] It's always really frustrating when I switch branches and then try to do my development and then realize that I have had my leftover database changes. And then having to go back and then always forgetting what order of operations to do to reverse the migration and then having to re-migrate. I know that pain very well.

JOËL: Something I've been doing for this project is when I switch branches, making sure that my structure SQL is checked out to the latest version from the main branch. So I have a clean structure SQL then I drop my local database, recreate an empty one, and run a rake db:schema:load. And that will load that structure file as it is on the main branch into the database schema.

That does not have any of the migrations on this branch run, so, at that point, I can run a rake db:migrate. And I will get exactly what's on main plus what gets generated on this branch and nothing else. And so, that's been a way that I've been able to kind of switch between branches and run database operations without getting any cross-contamination.

STEPHANIE: Cross-contamination. I like that term. Have you automated this at all, or are you doing this manually?

JOËL: Entirely manually. I could probably script some of this. Right now...so it's three steps, right? Drop, create, schema load. I just have them in one command because you can chain Unix commands with a double ampersand. So that's what I'm doing right now. I want to say there's a db:reset task, but I think that it uses migrate rather than schema load. And I don't want to actually run migrations.

STEPHANIE: Yeah, that would take longer. That's funny. I do love the up arrow key [laughs] in your terminal for, you know, going back to the thing you're running over and over again.

I also appreciate the couple extra seconds that you're spending in waiting for your database to recreate. Like, you're paying that cost upfront rather than down the line when you are in the middle of doing [laughs] what you're trying to do and realize, oh no, my database is not in the state that I want it to be for this branch.

JOËL: Or I'm dealing with some awful git conflict when trying to merge some of these branches. Or, you know, somebody comments on my PR and says, "Why are you touching the orders table? This change has nothing to do with orders." I'm like, "Oh, sorry, that actually came out of a different thing that I did." So, yep, keeping those diffs small.

STEPHANIE: Nice. Well, I'm glad that you found a way to manage it.

JOËL: So you mentioned the up arrow key and how that's really nice in the terminal. Something that I've been relying on a lot recently is reverse history search, CTRL+R in the terminal. That allows me to, instead of, like, going one by one in order of the history, filter for something that matches the thing that I've written. So, in this case, I'll hit CTRL+R, type, you know, Rails DB or whatever, then immediately it shows me, oh, did you want this long command? Hit enter, and I'm done. Even if I've done, you know, 20 git commands between then and the last time I ran it.

STEPHANIE: Yeah, that's a great tip.

So, a few weeks ago, we received a listener question from John, and he was responding to an episode where I'd asked about what the grammatical term is for verbs that are also nouns. He told us about the phrase, a verbal noun, for which there's a specific term called gerund, which is basically, in English, the words ending in ING. So, the gerund version of bike would be biking.

And he pointed out a really interesting relationship that gerunds have to data modeling, where you can use a gerund to model something that you might describe as a verb, especially as a user interaction, but can be turned into a noun to form a resource that you might want to introduce CRUD operations for in your application.

So one example that he was telling us about is the idea of maybe confirming a reservation. And, you know, we think of that as an action, but there is also a noun form of that, which is a confirmation. And so, confirmation could be a new resource, right? It could even be backed at the database level. And now you have a simpler way of representing the idea of confirming a reservation that is more about the confirmation as the resource itself rather than some kind of append them to a reservation itself.

JOËL: That's really cool. We get to have a crossover between grammar terms and programming, and being able to connect those two is always a fun day for me.

STEPHANIE: Yeah, I actually find it quite difficult, I think, to come up with noun forms of verbs on my own. Like, I just don't really think about resources that way. I'm so used to thinking about them in a more tangible way, I suppose. And it's really kind of cool that, you know, in the English language, we have turned these abstract ideas, these actions into, like, an object form.

JOËL: And this is particularly useful when we're trying to design RESTful either APIs or even just resources for a Rails app that's server-rendered so that instead of trying to create all these, like, extra actions on our controller that are verbs, we might decide to instead create new resources in the system, new nouns that people can do the standard 7 to.

STEPHANIE: Yes. I like that better than introducing custom controller actions or routes that deviate from RESTful conventions because, you know, I probably have seen a slash confirm reservation [laughs] URL. And, you know, this is, I think, an interesting way of avoiding having too many of those deviating endpoints.

JOËL: Yeah, I found that while Rails does have support for those, just all the built-in things play much more nicely if you're restricting yourself to the classic seven. And I think, in general, it's easier to model and think about things in a Rails app when you have a lot of noun resources rather than one giant controller with a bunch of kind of verb actions that you can do to it. In the more formal jargon, I think we might refer to that as RESTful style versus RPC style, a Remote Procedure Call.

STEPHANIE: Could you tell me more about Remote Procedure Calls and what that means?

JOËL: The general idea is that it's almost like doing a method call on an object somewhere. And so, you would say, hey, I've got an account, and I want to call the confirm method on it because I know that maybe underlying this is an ActiveRecord account model. And the API or the web UI is just a really thin layer over those objects. And so, more or less, whatever your methods on your object are, can be accessed through the API. So the two kind of mirror each other.

STEPHANIE: Got it. That's interesting because I can see how someone might want to do that, especially if, you know, the account is the domain object they're using at the, you know, persistence layer, and maybe they're not quite able to see an abstraction for something else. And so, they kind of want to try to fit that into their API design.

JOËL: So I have a perhaps controversial opinion, which is that the resources in your Rails application, so your controllers, shouldn't map one-to-one with your database tables, your models.

STEPHANIE: So, are you saying that you are more likely to have more abstractions or various resources than what you might have at the database level?

JOËL: Well, you know what? Maybe more, but I would say, in general, different. And I think because both layers, the controller layer, and the model layer, are playing with very different sets of constraints. So when I'm designing database tables, I'm thinking in terms of normalization. And so, maybe I would take one big concept and split it up into smaller concepts, smaller tables because I need this data to be normalized so that there's no ambiguity when I'm making queries. So maybe something that's one resource at the controller layer might actually be multiple tables at the database layer.

But the inverse could also be true, right? You might have, in the example that John gave, you know, an account that has a single table in the database with just a Boolean field confirmed yes or no. And maybe there's just a generic account resource. But then, separately, there's also a confirmation resource. And so, now we've got more resources at the controller layer than at the database layer. So I think it can go either way, but they're just not tightly coupled to each other.

STEPHANIE: Yeah, that makes sense. I think another way that I've seen this manifest is when, like you said, like, maybe multiple database tables need to be updated by, you know, a request to this endpoint. And now we get into [chuckles] what some people may call services or that territory of basically something. And what's interesting is that a lot of the service classes are named as verbs, right? So order, creator. And, like, whatever order of operations that needs to happen on multiple database objects that happens as a result of a user placing an order. But the idea that those are frequently named as verbs was kind of interesting to me and a bit of a connection to our new gerund tip.

JOËL: That's really interesting. I had not made that connection before. Because I think my first instinct would be to avoid a service object there and instead use something closer to a form object that takes the same idea and represents it as a noun, potentially with the same name as the resource. So maybe leaning really heavily into that idea of the verbal noun, not just in describing the controller or the route but then also maybe the object backing it, even if it's not connecting directly to a database table.

STEPHANIE: Interesting. So, in this case, would the form object be mapped closer to your controller resource?

JOËL: Potentially, yes. So maybe I do have some kind of, like, object that represents a confirmation and makes it nicer to render the confirmation form on the edit page or the new page. In this case, you know, it's probably just one checkbox, so maybe it's not worth creating an object. But if there were multiple fields, then yes, maybe it's nice to create an in-memory object that has the same name as the resource. Similar maybe for a resource that represents multiple underlying database tables. It can be nice to have kind of one object that represents all of them, almost like a facade, I guess.

STEPHANIE: Yeah, that's really interesting. I like that idea of a facade, or it's, like, something at a higher level representing hopefully, like, some kind of meaning of all of these database objects together.

JOËL: I want to give a shout-out to talk from a former thoughtboter, Derek Prior—actually, former Bike Shed host—from RailsConf 2017 called In Relentless Pursuit of REST, where he digs into a lot of these concepts, particularly how to model resources in your Rails app that don't necessarily map one to one with a database table, and why that can be a good thing. Have you seen that talk?

STEPHANIE: I haven't, but I love the title of it. It's a great pun. It's very evocative, I think because I'm really curious about this idea of a relentless pursuit. Because I think another way to react to that could be to be done with REST entirely and maybe go with something like GraphQL.

JOËL: So instead of a relentless pursuit, it's a relentless...what's the opposite of pursuing? Fleeing?

STEPHANIE: Fleeing? [laughs] I like how we arrived there at the same time. Yes. So now I'm thinking of I had mentioned a little bit ago on the show we had our spicy takes Lightning Talks on our Boost Team. And a fellow thoughtboter, Chris White, he had given a talk about Why REST Is Not the Best and for --

JOËL: Also, a great title.

STEPHANIE: Yes, also, a great title.

JOËL: I love the rhyming there.

STEPHANIE: Yeah. And his reaction to the idea of trying to conform user interactions that don't quite map to a noun or an obvious resource was to potentially introduce GraphQL, where you have one endpoint that can service really anything that you can think of, I suppose. But, in his example, he was making the argument that human interactions are not database resources, right?

And maybe if you're not able to find that abstraction as a noun or object, with GraphQL, you can encapsulate those ideas as closer to actions, but in the GraphQL world, like, I think they're called mutations. But it is, I think, a whole world of, like, deciding what you want to be changed on the server side that is a little less constrained to having to come up with the right abstraction.

JOËL: I feel like GraphQL kind of takes that, like, complete opposite philosophy in that instead of saying, hey, let's have, like, this decoupling between the API layer and the database, GraphQL almost says, "No, let's lean into that." And yeah, you want to traverse the graph of, like, tables under the hood? Absolutely. You get to know the tables. You get to know how they're related to each other.

I guess, in theory, you could build a middle layer, and that's the graph that gets traversed rather than the graph of the tables. In practice, I think most people build it so that the API layer more or less has access directly to tables. Has that been your experience?

STEPHANIE: That's really interesting that you brought that up. I haven't worked with GraphQL in a while, but I was reading up on it before we started recording because I was kind of curious about how it might play with what we're talking about now. But the idea that it's graphed based, to me, was like, oh, like, that naturally, it could look very much like, you know, an entity graph of your relational database.

But the more I was reading about the GraphQL schema and different types, I realized that it could actually look quite different. And because it is a little bit closer to your UI layer, like, maybe you are building an abstraction that is more for serving that as that middle layer between your front end and your back end.

JOËL: That's really interesting that you mentioned that because I feel like the sort of traditional way that APIs are built is that they are built by the back-end team. And oftentimes, they will reflect the database schema. But you kind of mentioned with GraphQL here, sometimes it's the opposite that happens. Instead of being driven kind of from the back towards the front, it might be driven from the front towards the back where the UI team is building something that says, hey, we need these objects. We need these connections. Can you expose them to us? And then they get access to them.

What has been your experience when you've been working with front ends that are backed by a GraphQL API?

STEPHANIE: I think I've tended to see a GraphQL API when you do have a pretty rich client-side application with a lot of user interactions that then need to, you know, go and fetch some data. And you, like, really, you know, obviously don't want a page reload, right?

So it's really interesting, actually, that you pointed out that it's, like, perhaps the front end or the UI driving the API. Because, on one hand, the flexibility is really nice. And there's a lot more freedom even in maybe, like, what the product can do or how it would look. On the other hand, what I've kind of also seen is that eventually, maybe we do just want an API that we can talk to separate from, you know, any kind of UI. And, at that point, we have to go and build a separate thing [laughs] for the same data.

JOËL: So we've been talking about structuring APIs and, like, boundaries and things like that. I think my personal favorite feature of GraphQL is not the graph part but the fact that it comes with a built-in schema. And that plays really nicely with some typed technologies. Particularly, I've used Elm with some of the GraphQL libraries there, and that experience is just really nice. Where it will tell you if your front-end code is not compatible with the current API schema, and it will generate some things based off the schema.

So you have this really nice feedback cycle where somebody makes a change to the API, or you want to make a change to the code, and it will tell you immediately is your front end compatible with the current state of the back end? Which is a classic problem with developing front-end code.

STEPHANIE: First of all, I think it's very funny that you admitted to not preferring the graph part of GraphQL as a graph enthusiast yourself. [laughs] But I think I'm in agreement with you because, like, normally, I'm looking at it in its schema format. And that makes a lot of sense to me.

But what you said was really interesting because, in some ways, we're now kind of going back to the idea of maybe boundaries blurring because the types that you are creating for GraphQL are kind of then servicing both your front end and your back end. Do you think that's accurate?

JOËL: Ooh. That is an important distinction. I think you can. And I want to say that in some TypeScript implementations, you do use the types on both sides. In Elm, typically, you would not unless there's something really primitive, like a string or something like that.

STEPHANIE: Okay, how does that work?

JOËL: So you have some conversion layer that happens.

STEPHANIE: Got it.

JOËL: Honestly, I think that's my preference, and not just at the front end versus API layer but kind of all throughout. So the shape of an object in the database should not be the same shape as the object in the business logic that runs on the back end, which should not be the same shape as the object in transport, so JSON or whatever, which is also not the same shape as the object in your front-end code. Those might be similar, but each of these layers has different responsibilities, different things it's trying to optimize for.

Your code should be built, in my opinion, in a way that allows all four of those layers to diverge in their interpretation of not only what maybe common entities are, so maybe a user looks slightly different at each of these layers, but maybe even what the entities are to start with. And that maybe in the database what, we don't have a full user, we've got a profile and an account, and those get merged somehow. And eventually, when it gets to the front end, all we care about is the concept of a user because that's what we need in that context.

STEPHANIE: Yeah, that's really interesting because now it almost sounds like separate systems, which they kind of are, and then finding a way to make them work also as one bigger [laughs] system. I would love to ask, though, what that conversion looks like to you. Or, like, how have you implemented that? Or, like, what kind of pattern would you use for that?

JOËL: So I'm going to give a shout-out to the article that I always give a shout-out to: Parse, Don't Validate. In general, yeah, you do a transformation, and potentially it can fail. Let's say I'm pulling data from a GraphQL API into an Elm app. Elm has some built-in libraries for doing those transformations and will tell you at compile time if you're incorrectly transforming the data that comes from the shape that we expect from the schema.

But just because the schema comes in as, like, a flat object with certain fields or maybe it's a deeply nested chain of objects in GraphQL, it doesn't mean that it has to be that way in your Elm app. So that transformation step, you get to sort of make it whatever you want.

So my general approach is, at each layer, forget what other people are sending you and just design the entities that you would like to. I've heard the term wish-driven development, which I really like. So just, you know, if you could have, like, to make your life easy, what would the entities look like? And then kind of work backwards from there to make that sort of perfect world a reality for you and make it play nicely with other systems. And, to me, that's true at every layer of the application.

STEPHANIE: Interesting. So I'm also imagining that the transformation kind of has to happen both ways, right? Like, the server needs a way to transform data from the front end or some, you know, whatever, third party. But that's also true of the front end because what you're kind of saying is that these will be different. [laughs]

JOËL: Right. And, in many ways, it has to be because JSON is a very limited format. But some of the fancier things that you might have access to either on the back end or on the front end might be challenging to represent natively in JSON. And a classic one would be what Elm calls a custom type. You know, they're also called tagged unions, discriminated unions, algebraic data types. These things go by a bajillion names, and it's confusing.

But they're really kind of awkward and hard, almost impossible to represent in straight-up JSON because JSON is a very limited kind of transportation format. So you have to almost, like, have a rehydration step on one side and a kind of packing down step on the other when you're reading or writing from a JSON API.

STEPHANIE: Have you ever heard of or played that Wikipedia game Getting to Philosophy?

JOËL: I've done, I think, variations on it, the idea that you have a start and an end article, and then you have to either get through in the fewest amount of clicks, or it might be a timed thing, whoever can get to the target article first. Is that what you're referring to?

STEPHANIE: Yeah. So, in this case, I'm thinking, how many clicks through Wikipedia to get to the Wiki article about philosophy? And that's how I'm thinking about how we end up getting to [laughs] talking about types and parsing, and graphs even [laughs] on the show.

JOËL: It's all connected, almost as if it forms a graph of knowledge.

STEPHANIE: Learning that's another common topic on the show. [laughs] I think it's great. It's a lot of interesting lenses to view, like, the same things and just digging further and further deeper into them to always, like, come away with a little more perspective.

JOËL: So, in the vein of wish-driven development, if you're starting a brand-new front-end UI, what is your sort of dream approach for working with an API?

STEPHANIE: Wish-driven development is very visceral to me because I often think about when I'm working with legacy code and what my wishes and dreams were for the, you know, the stack or the technology or whatever. But, at that point, I don't really have the power to change it. You know, it's like I have what I have. And that's different from being in the driver's seat of a greenfield application where you're not just wishing. You're just deciding for yourself. You get to choose.

At the end of the day, though, I think, you know, you're likely starting from a simple application. And you haven't gotten to the point where you have, like, a lot of features that you have to figure out how to support and, like, complexity to manage. And, you know, you don't even know if you're going to get there. So I would probably start with REST.

JOËL: So we started this episode from a very back-end perspective where we're talking about Rails, and routes, and controllers. And we kind of ended it talking from a very front-end perspective. We also contrasted kind of a more RESTful approach, versus GraphQL, versus more kind of old-school RPC-style routing.

And now, I'm almost starting to wonder if there's some kind of correlation between whether someone primarily works from the back end and maybe likes, let's say, REST versus maybe somebody on the front end maybe preferring GraphQL. So I'd be happy for any of our listeners who have strong opinions preferring GraphQL, or REST, or something else; message us at [email protected] and let us know. And, if you do, please let us know if you're primarily a front-end or a back-end developer because I think it would be really fun to see any connections there.

STEPHANIE: Absolutely. On that note, shall we wrap up?

JOËL: Let's wrap up.

STEPHANIE: Show notes for this episode can be found at bikeshed.fm.

JOËL: This show has been produced and edited by Mandy Moore.

STEPHANIE: If you enjoyed listening, one really easy way to support the show is to leave us a quick rating or even a review in iTunes. It really helps other folks find the show.

JOËL: If you have any feedback for this or any of our other episodes, you can reach us @_bikeshed, or you can reach me @joelquen on Twitter.

STEPHANIE: Or reach both of us at [email protected] via email.

JOËL: Thanks so much for listening to The Bike Shed, and we'll see you next week.

ALL: Byeeeeeee!!!!!!

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