Skip to main content

Solving Room "cannot find setter for field" error in build time

Room persistence library is one of the easiest one to set up. However, when using data classes for your Room entities, you might face some small problem, which on the first look doesn't really make any sense.

Let's try to compile this class:

The problem:

And so will happen with other fields

But I already have a data class entity that has only vals.  Why doesn't this class compile?
The problem here is the class UserGrade that room has no idea how give a value to it. Furthermore, that's a non nullable type. Even though I'm ignoring it from Room, the compiler cannot continue because it's the constructor that is checked first, thus failing all my other values to be set.

So, a small fix for this, is that make every variable a var instead of val and make our object nullable type. It's not a bad solution, but now I have to define a constructor, to tell Room that these are the default values from it: 

The solution

Perhaps it is not such a big deal, but when chances are, why not try a better approach? Also, it might be a little problematic to break the standardization of the entities. Having a data class with vals and a data class with vars for the same purpose, is not a good style, at least for me. 

Let's re roll to immutable variables and place a default value on our UserGrade object:

If you try to build, the same error will appear. The compiler will still yell at you. Even though the problem still persists from Room library, it's not its fault. That's because when Kotlin compiles to Java, it has no idea what default values in parameters are.  

The last approach of this use case is to add the @JvmOverloads annotation before the constructor, so Java will know to create the constructor overloading for us:

And that's it. Good luck!

You can follow me on twitter.

Popular posts from this blog

Modularizing your Android app, breaking the monolith (Part 1)

Inspired by a Martin Fowlers post about Micro Frontends, I decided to break my monolithic app into a modular app. I tried to read a little more about breaking monolithic apps in Android, and as far as I got, I felt confident to share my experience with you. This will be some series of blog posts where we actually try to break a simple app into a modularized Android app.

Note: You should know that I am no expert in this, so if there are false statements or mistakes please feel free to criticize, for the sake of a better development. 

What do you benefit from this approach:
Well, people are moving pretty fast nowadays and delivery is required faster and faster. So, in order to achieve this, modularising Android apps is really necessary.You can share features across different apps. Independent teams and less problems per each.Conditional features update.Quicker debugging and fixing.A feature delay doesn't delay the whole app. As per writing tests, there is not too much difference about…

From Gson to Moshi, what I learned

There is no doubt that people are getting away from GSON and I agree with those reasons too. The only advantage GSON has over other parsing libraries is that it takes a really short amount of time to set up. Furthermore, the most important thing is that Moshi is embracing Kotlin support.

First let's implement the dependency:
implementation("com.squareup.moshi:moshi:1.8.0") It's not a struggle to migrate to Moshi. It's really Gson look-a-like. The only thing to do is annotate the object with @field:Json instead of @SerializedName (which is Gsons way for JS representation):

data class User( //GSON way @SerializedName("name") val name: String, @SerializedName("user_name") val userName: String, @SerializedName("last_name") val lastName: String, @SerializedName("email") val email: String ) data class User( //Moshi way @field:Json(name = "name") val name: String, @field:Json(name = "user_name…

Modularizing your Android app, breaking the monolith (Part 2)

This is part 2 of a series of articles about modularizing Android app. If you haven't yet read the first article, you may find it here.

On our first article we just moved some classes outside the application and applied as an independent module. But what if we have dependencies pulled from the application level? This could be a small challenge. First of all, we want to clarify on how are we going to modularize the app. And depending on the previous article, I chose the by feature version of modularization. First of all, let's show some dependencies that are going to be needed in the whole app.

Note: I'm using Dagger for handling dependencies but manual DI or any dependency tool should be fine to understand this part.

So, this is my dependency schema:

Well, it's not that bad, but this isn't what we want to transform to when trying to modularize the app. If you think about it, modules that don't need a dependency, can get it quite easily. For example: A FeatureXVi…