Migrate model from Java class to Kotlin data class

Fix build error "Entities and Pojos must have a usable public constructor" by updating Room from 1.0.0 to 1.1.1

Entities and Pojos must have a usable public constructor. You can have an empty constructor or a constructor whose parameters match the fields (by name and type).

florina-muntenescu commented on 14 Oct 2017 Thanks @rs146 for reporting this. The problem here is that Room can't find the right constructor for the elements in the relation, when the element is Int (or Integer in Java). I created an issue on our internal tracker for this but chances are this won't be fixed for the 1.0 release, unfortunately. https://github.com/googlesamples/android-architecture/issues/434

Fix error "IllegalArgumentException: Parameter specified as non-null is null:

The exception is pretty clear: you're passing null for the parameter. By default all variables and parameters in Kotlin are non-null. If you want to pass null parameter to the method you should add ? to it's type. https://stackoverflow.com/questions/44885783/illegalargumentexception-parameter-specified-as-non-null-is-null

-    constructor(id: Int, title: String, description: String, imageHref: String) {
+    constructor(id: Int, title: String?, description: String?, imageHref: String?) {

     @Ignore
-    constructor(title: String, description: String, imageHref: String) {
+    constructor(title: String?, description: String?, imageHref: String?) {

总结：如果数据可能为null，一定要后缀?

自动转成的Kotlin代码仍然是Java style，需要修改为 Kotlin data class 定义 properties 的方式

@Entity(tableName = "ArticleTable", indices = [Index(value = *arrayOf("title"), unique = true)])
data class Article (

    @PrimaryKey(autoGenerate = true)
    val id: Int = 0,

    @SerializedName("title")
    val title: String?,

    @SerializedName("description")
    val description: String?,

    @SerializedName("imageHref")
    val imageHref: String?
)

Kotlin 可以通过下述方式初始化 data class

return Article(title = title, description = description, imageHref = imageHref)

2018-08-27 Weiyi Li