Kotlin Realm: Class must declare a public constructor with no arguments if it contains custom constructors

I'm creating a **Realm** object in **Kotlin**.

**Realm Object:**

open class PurposeModel(var _id: Long?,
var purposeEn: String?,
var purposeAr: String?) : RealmObject()

When I compile the above code I'm getting this error:

error: Class "PurposeModel" must declare a public constructor with no arguments if it contains custom constructors.

I can't find any question related to this in Kotlin. How do I resolve this?

You can also use the [Kotlin no-arg plugin][1] which generates a no-arg constructor for you.


[1]:

[To see links please register here]

That's why I prefer to define them like this

open class PurposeModel : RealmObject() {
@field:PrimaryKey
var id: Long? = null
var purposeEn: String? = null
var purposeAr: String? = null
}

**Error:**

_id, purposeEn, purposeAr not initialized

**Solution**

open class PurposeModel(
var _id: Long? = 0,
var purposeEn: String? = "",
var purposeAr: String? = ""
) : RealmObject()

To clear this error you have to assign default values to properties.

Change the Realm Object like this:

open class PurposeModel(
var _id: Long? = 0,
var purposeEn: String? = null,
var purposeAr: String? = null
) : RealmObject()

Now it will compile.

**Reason:**

> When the default value not assigned it will become the parameters of
> the constructor, Realm need a public constructor with no arguments.
> When the default value assigned, it will become the properties of the
> class. So you will get empty constructor by default and clean code.

I use Realm on my Ktor server and you need to provide an empty constructor with default values.


@Serializable
class User(
val id: String,
var email: String,
var hashedPass: ByteArray,
) : RealmObject {
constructor() : this(
id = ObjectId.create().toString(),
email = "",
hashedPass = byteArrayOf()
) // Empty constructor for Realm
}

Without it, I was getting and error:

[Realm] Cannot find primary zero arg constructor

For me the solution was adding the `abstract` keyword, below is my working code,

```kotlin
@Log4j2
@RunWith(MockitoJUnitRunner::class)
@ExtendWith(MockitoExtension::class)
internal abstract class ItemsManagementControllerTest(
private val logger: Logger = LoggerFactory.getLogger(
ItemsManagementControllerTest::class.java
) as Logger,
private var mvc: MockMvc? = null,
@InjectMocks private val itemsManagementController: ItemsManagementController? = null,
@Mock private val itemRepository: ItemRepository? = null
) {
```

Removing the `abstract` keywords fails the test cases in the class. I honestly do not understand why at the moment.