Kotlin Room can't add new object to viewmodel repository due to required long when creating object from user input

Issue

I have created entity class with auto generated id.

@Entity(tableName = "todo_list")
data class Todo(
@PrimaryKey(autoGenerate = true)
var itemId: Long = 0L,
@ColumnInfo(name = "todo_title")
val title: String,
@ColumnInfo(name = "todo_description")
val description: String)

And viewmodel class

class TodoViewModel(application: Application) : AndroidViewModel(application) {

val readAllData: LiveData<List<Todo>>
private val repository: TodoRepository

init {
    val todoDao = TodoDatabase.getInstance(application).todoDao()
    repository = TodoRepository(todoDao)
    readAllData = repository.readAllData
}

fun addTodo(todo: Todo) {
    viewModelScope.launch(Dispatchers.IO) {
        repository.addTodo(todo)
    }
}

fun deleteTodo(todo: Todo) {
    viewModelScope.launch (Dispatchers.IO ){
        repository.deleteTodo(todo = todo)
    }
  }
}

But when I wanna add todo entry on button click it still requires to add long.

mTodoViewModel.addTodo(Todo(titleText, descriptionText))

Am I adding new object wrong or there is any way to fix it?

Solution

The problem is data class constructor requires 3 parameters but only 2 are being passed.

now even though, you have provided a default value to the data class but since it comes first in the data class, it needs to be defined even if the value is the same,i.e., 0L.

I have four suggestions, you can use whichever suits you best.

1. Pass 0L as the key.

should look something like this-

mTodoViewModel.addTodo(Todo(0L, titleText, descriptionText))

or

fun addTodo(titleText:String, descriptionText:String) {
    viewModelScope.launch(Dispatchers.IO) {
        repository.addTodo(Todo(0L, titleText,descriptionText))
    }
}

2. Slightly change the database structure.

@Entity(tableName = "todo_list")
data class Todo(

    @ColumnInfo(name = "todo_title")
    val title: String,
    @ColumnInfo(name = "todo_description")
    val description: String,
    @PrimaryKey(autoGenerate = true)
    var itemId: Long = 0L
)

Here since the default value is in the last there is no need to send 0L

3. Use a secondary constructor with your data class.

should look something like this -

@Entity(tableName = "todo_list")
data class Todo(
    @PrimaryKey(autoGenerate = true)
    var itemId: Long = 0L,
    @ColumnInfo(name = "todo_title")
    val title: String,
    @ColumnInfo(name = "todo_description")
    val description: String
) {
    constructor(title: String, description: String) : this(title, description, 0L)
}
Here now you have 2 constructors one with 3 parameters, the other with 2.

4. assign values directly to each constructor something like this.

Todo(title = titleText, description = descriptionText)

Here automatically OL will be considered

I believe all of these should work perfectly fine. If you have any further doubts feel free to leave a comment.

Answered By - lets start coding