在SQLite Android中为关系生成和使用外键

我有一个android studio应用程序，我可以在其中添加公司，在这些公司中，我还可以添加员工。现在，我正在尝试获取员工列表，该列表仅显示我之前在显示员工的独特活动中选择的公司的元素

我创建了两个类：

data class Company(val id:Int, val name:String, val telephone:String)
data class Employee (val id:Int, val name:String, val telephone:String, val idCompany:Int)

在我的SQLiteHelper中，我为每个表创建了表，在Employees中使用一个外键来建立关系

    private val TABLE_COMPANY = "CompanyTable"
    private val TABLE_EMPLOYEE = "EmployeeTable"


    //Company table
    private val COMPANY_ID = "_id"
    private val COMPANY_NAME = "name"
    private val COMPANY_TL = "telephone"

    //Employee table
    private val EMPLOYEE_ID = "id"
    private val EMPLOYEE_NAME = "name"
    private val EMPLOYEE_TL = "telephone"
    private val EMPLOYEE_COMPANY_ID = "id"



}

override fun onCreate(db: SQLiteDatabase?) {

    val CREATE_COMPANY_TABLE = ("CREATE TABLE " + TABLE_COMPANY + "("
            + COMPANY_ID + " INTEGER PRIMARY KEY,"
            + COMPANY_NAME + " TEXT,"
            + COMPANY_TL + " TEXT" + ")")

    val CREATE_EMPLOYEE_TABLE = ("CREATE TABLE " + TABLE_EMPLOYEE + "("
            + EMPLOYEE_ID + " INTEGER PRIMARY KEY,"
            + EMPLOYEE_NAME + " TEXT,"
            + EMPLOYEE_TL + " INTEGER,"
            + EMPLOYEE_COMPANY_ID + " INTEGER,"
            + " FOREIGN KEY ("+ EMPLOYEE_COMPANY_ID+") REFERENCES "+TABLE_COMPANY+"("+ COMPANY_ID+"))")


    db?.execSQL(CREATE_EMPLOYEE_TABLE)
    db?.execSQL(CREATE_COMPANY_TABLE)

}

所以，我用recyclerviews做了两个活动，一个是为公司做的，另一个是为员工做的。 当我单击一家公司时，“员工”活动将打开，并显示他们的列表

但它显示了我所有的员工，所以我想知道如何只显示我保存的员工，他们的id与我在上一次活动中单击的公司id相同

但我现在不知道该怎么办

以下是向员工展示的DAO函数：

fun viewEmployee(): ArrayList<Employee> {

    val empList: ArrayList<Employee> = ArrayList<Employee>()

    // Query to select the records
    val selectQuery = "SELECT L.$EMPLOYEE_NAME, L.$EMPLOYEE_TL, L.$EMPLOYEE_ID, L.$EMPLOYEE_COMPANY_ID, C.$COMPANY_ID" +
            "FROM $TABLE_EMPLOYEE as L, $TABLE_COMPANY as C" +
            "WHERE L.$EMPLOYEE_COMPANY_ID = C.$COMPANY_ID"



    val db = this.readableDatabase
   
    var cursor: Cursor? = null

    try {
        cursor = db.rawQuery(selectQuery, null)

    } catch (e: SQLiteException) {
        db.execSQL(selectQuery)
        return ArrayList()
    }

    var id: Int
    var name: String
    var telephone: String
    var idCompany: Int

    if (cursor.moveToFirst()) {
        do {
            id = cursor.getInt(cursor.getColumnIndex(EMPLOYEE_ID))
            name = cursor.getString(cursor.getColumnIndex(EMPLOYEE_NAME))
            telephone = cursor.getString(cursor.getColumnIndex(EMPLOYEE_TL))
            idCompany = cursor.getInt(cursor.getColumnIndex(EMPLOYEE_COMPANY_ID))

            val employee = Employee(id = id, name = name, telephone = telephone, idCompany = idCompany)
            empList.add(employee)

        } while (cursor.moveToNext())
    }
    return empList
}

下面是展示员工的活动

class ManagerEmp : AppCompatActivity() {




override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_manager_emp)

    setList()
    
    createEmp.setOnClickListener{
        val intent = Intent(this, CreateEmp::class.java)
        startActivity(intent)
    }
}





/**
 * Gets DB employee list
 */
private fun getItemsList(): ArrayList<Employee> {
    //creating the instance of DatabaseHandler class
    val databaseHandler = DataBaseHelper(this)
    //calling the viewEmployee method of DatabaseHandler class to read the records
    val empList: ArrayList<Employee> = databaseHandler.viewEmployee()

    return empList
}



/**
 * Generates the list
 */
private fun setList() {

    recyclerEmp.layoutManager = LinearLayoutManager(this)
    val itemAdapter = empAdapter(this, getItemsList())
    recyclerEmp.adapter = itemAdapter
}

}

这听起来很简单，但至少对我来说不是 我想获取公司的id值并将其传递给employee list活动，这样我就可以使用它进行比较，但是idk how，我对kotlin和编程一般来说都是新手

如果你能给出答案，你就是在救我的命

首先，您必须获得要筛选的公司ID。例如，可以通过以下方式完成

然后您将需要额外的查询，该查询将用于按companyId进行筛选

例如，如果companyId存储在filteredCompanyId变量中，则可以添加其他筛选条件，其中。。。C.$COMPANY_ID==$filteredCompanyId:

---

您好，如果您使用Android的Room Api，您就不必管理光标等了。。。看，关于你的问题。所以，我必须在我的DAO中定义一个Int变量，并在查询中使用它？好的，我刚刚做了，我在DAO函数中添加了一个过滤参数，然后，在公司活动中，我使用了一个意图，将单击的公司的id传递给员工活动。然后我将该id称为companyId，并调用将companyId val放入参数中的DAO函数。谢谢

val filteredCompanyId = 5
val query = """
SELECT L.$EMPLOYEE_NAME, 
       L.$EMPLOYEE_TL, 
       L.$EMPLOYEE_ID, 
       L.$EMPLOYEE_COMPANY_ID, 
       C.$COMPANY_ID 
FROM   $TABLE_EMPLOYEE AS L, 
       $TABLE_COMPANY AS C 
WHERE  L.$EMPLOYEE_COMPANY_ID = C.$COMPANY_ID 
       AND C.$COMPANY_ID == $filteredCompanyId
"""