完整错误: 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).

百度翻译：

错误：实体和POJO必须具有可用的公共构造函数。可以有一个空构造函数或一个其参数与字段匹配的构造函数（按名称和类型）。

意思是说必须构造一个函数，中文网文档也没有说明要构造一个函数，不知道是不是没有找到。

解决：

Kotlin：实体和Pojos必须有一个可用的公共构造函数

@Entity(tableName = "wan_bean")
data class WanBean (
    @Ignore val children: List<Any>?,
    @ColumnInfo(name = "courseId_") var courseId: Int?,
    @field:PrimaryKey(autoGenerate = true) var id: Int?,
    @ColumnInfo(name = "name_") var name: String?,
    @ColumnInfo(name = "order_") var order: Int?,
    @ColumnInfo(name = "parentChapterId_") var parentChapterId: Int?,
    @ColumnInfo(name = "userControlSetTop_") var userControlSetTop: Boolean?,
    @ColumnInfo(name = "visible_") var visible: Int?
){
    constructor() : this(null,UNKNOWN,UNKNOWN,"", UNKNOWN,UNKNOWN,false,UNKNOWN)

}

应该可以解决了！！！