Android room. error: Cannot figure out how to read this field from a cursor - android-room

Question

the SQLite database contains three tables 1) employee 2) skills 3) departments. The idea is this - the employee table stores data such as id, name, last_name, salary. Also, an employee has data such as skill and department, but there can be several data for one employee, so I created two separate skills and departments tables and linked them using the key to the employee table where the primary key for employee is id. Now with the help of id I need to display all the information about employee including his skills which can be several and departments. I implement the whole process using the ROOM library.
Here is the request I make
#Query("SELECT employ.id ,employ.name ,employ.last_name, employ.salary, " +
"skill.skill, department.department_name FROM employ INNER JOIN skill,department " +
"ON employ.id = :id AND skill.employ_id = :id AND department.employ_id = :id ")
AllAboutEmployee getAllAboutEmployee(String id);
Here is the AllAboutEmployee class whose object accepts the result of the request
public class AllAboutEmployee {
#ColumnInfo(name = "id")
private String id;
#ColumnInfo(name = "name")
private String name;
#ColumnInfo(name = "last_name")
private String lastName;
#ColumnInfo(name = "salary")
private String salary;
#ColumnInfo(name = "department_name")
private List<String> departmentsList; // THE ERROR IS ON THIS LINE
#ColumnInfo(name = "skill")
private List<String> skillList; // THE ERROR IS ON THIS LINE
public AllAboutEmployee(String id, String name, String lastName, String salary, List<String> departmentsList, List<String> skillList) {
this.id = id;
this.name = name;
this.lastName = lastName;
this.salary = salary;
this.departmentsList = departmentsList;
this.skillList = skillList;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getSalary() {
return salary;
}
public void setSalary(String salary) {
this.salary = salary;
}
public List<String> getDepartmentsList() {
return departmentsList;
}
public void setDepartmentsList(List<String> departmentsList) {
this.departmentsList = departmentsList;
}
public List<String> getSkillList() {
return skillList;
}
public void setSkillList(List<String> skillList) {
this.skillList = skillList;
}
}
So ther are two fields int the AllAboutEmployee class with the List type, in order to put several skills and several departments there. It is in these fields that an error occurs. Thank you in advance for your help

Answer 1

Wow.. that's so cool.. I was coding all day and got this error too!
You have to create a TypeCoverter to store your data into your Room's Database.
In this case you have two List, that are not types recognizable by Database, so you have to create an Converter for it to store as a String, and another method to do the inverse.
Something like:
class TypeCoverter{
#TypeConverter
fun arrayListToString(arrayList: ArrayList<String>?): String? {
if (arrayList.isNullOrEmpty()) return null
val string = StringBuilder()
for (item in arrayList) {
val isNotTheLastItemInTheArrayList = (item == arrayList.last()).not()
if (isNotTheLastItemInTheArrayList) {
string.append(item).append(COMMA)
} else {
string.append(item)
}
}
return string.toString()
}
}
#TypeConverter
fun stringToArrayList(string: String?): ArrayList<String>? {
when {
string.isNullOrEmpty() -> {
return null
}
string.contains(COMMA).not() -> {
val list = ArrayList<String>()
list.add(string)
return list
}
else -> {
return string.split(COMMA.toRegex()).dropLastWhile { it.isEmpty() } as ArrayList<String>
}
}
}
That's actually in Kotlin, but you can see how it works.