外键约束在sqlite android studio中不起作用

Question

I have two tables. TABLE_ADD_SUBSTATION is parent table and TABLE_ADD_FEEDER is child table . I am able to add data in child table in the foreign key which does not even exist in parent table. There is no error while inserting in foreign key. What is wrong here? Am I missing something. I am new to android studio.

public class DBHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "DATABASE.db";
    private static final String TABLE_ADD_SUBSTATION = "ADD_SUBSTATION";
    private static final String TABLE_ADD_FEEDER = "ADD_FEEDER";
    private static final int DATABASE_VERSION = 3;
public DBHelper(Context context){
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onConfigure(SQLiteDatabase db) {
        db.setForeignKeyConstraintsEnabled(true);
        super.onConfigure(db);
    }
 @Override
    public void onCreate(SQLiteDatabase db) {
//table for adding substation
        String createAddSubstationTable = "create table " + TABLE_ADD_SUBSTATION
                + "(substationNo INT(5) PRIMARY KEY, substationName VARCHAR(30), type VARCHAR(3), "
                + "serialNo INT(10), dateOfInstallation VARCHAR, totalCapacity INT, circle VARCHAR(10), "
                + "location VARCHAR(20), incomingSubstation int, newFeeder VARCHAR(10), newMeter VARCHAR(10))";
        db.execSQL(createAddSubstationTable);

        //table for adding feeder
        String createAddFeederTable = "create table " + TABLE_ADD_FEEDER
                +"(feederNo INT(5) PRIMARY KEY, typeOfConductor VARCHAR(30), conductorCapacity INT(10), incomingLine INT(10), "
                + "outgoingLine INT(10), totalLoad INT(10), totalNoOfConnection INT(10), status INT,"
                + "feederName VARCHAR(30), feederLength INT(10), substationNo INT(5) NOT NULL,"
                + " FOREIGN KEY(substationNo) REFERENCES TABLE_ADD_SUBSTATION(substationNo))";
        db.execSQL(createAddFeederTable);
}

 @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists " + TABLE_ADD_SUBSTATION);
        db.execSQL("drop table if exists " + TABLE_ADD_FEEDER);
       
        //create table again
        onCreate(db);
    }


 //function to add a substation into database
    public char addSubstationIntoDatabase(int substationNo, String substationName, String type, int serialNo,String dateOfInstallation, int totalCapacity, String circle, String location,
                                   int incomingSubstation){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();

        contentValues.put("substationNo", substationNo);
        contentValues.put("substationName",substationName);
        contentValues.put("type", type);
        contentValues.put("serialNo",serialNo);
        contentValues.put("dateOfInstallation", dateOfInstallation);
        contentValues.put("totalCapacity",totalCapacity);
        contentValues.put("circle", circle);
        contentValues.put("location", location);
        contentValues.put("incomingSubstation", incomingSubstation);

        long result = db.insert(TABLE_ADD_SUBSTATION, null, contentValues);
        if(result == -1){
            Cursor cursor = db.rawQuery("Select substationNo from ADD_SUBSTATION where substationNo = ?", new String[]{String.valueOf(substationNo)});
            if(cursor.getCount()>0)
                return 'B';
            else return 'C';
        }
        else
            return 'D';

    }



 //function to add feeder into database
    public boolean addFeederIntoDatabase(int feederNo,String feederName, int feederLength, String typeOfConductor,
                                         int conductorCapacity, int incomingLine, int outgoingLine, int totalLoad,
                                         int totalNoOfConnection, int status, int substationNo){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();


        contentValues.put("feederNo", feederNo);
        contentValues.put("feederName",feederName);
        contentValues.put("feederLength", feederLength);
        contentValues.put("typeOfConductor", typeOfConductor);
        contentValues.put("conductorCapacity", conductorCapacity);
        contentValues.put("incomingLine", incomingLine);
        contentValues.put("outgoingLine",outgoingLine);
        contentValues.put("totalLoad", totalLoad);
        contentValues.put("totalNoOfConnection", totalNoOfConnection);
        contentValues.put("status", status);
        contentValues.put("substationNo", substationNo);
        Log.d("contentValues", String.valueOf(contentValues));

        long result = db.insert(TABLE_ADD_FEEDER, null, contentValues);
        db.close();
        if(result == -1)
            return false;
        else
            return true;
}```

Answer 1

In the method onCreate() you construct the string createAddFeederTable by concatenating sql keywords, table names and column names.
But you use TABLE_ADD_SUBSTATION as the name of the table which is referenced by the column substationNo and this is wrong.
TABLE_ADD_SUBSTATION is a variable and not the table's name.

Change your code to this:

String createAddFeederTable = "create table " + TABLE_ADD_FEEDER
        +"(feederNo INT(5) PRIMARY KEY, typeOfConductor VARCHAR(30), conductorCapacity INT(10), incomingLine INT(10), "
        + "outgoingLine INT(10), totalLoad INT(10), totalNoOfConnection INT(10), status INT,"
        + "feederName VARCHAR(30), feederLength INT(10), substationNo INT(5) NOT NULL,"
        + "FOREIGN KEY(substationNo) REFERENCES "
        + TABLE_ADD_SUBSTATION
        + "(substationNo))";
db.execSQL(createAddFeederTable);

After this change, uninstall the app from the device to delete the database and rerun to recreate it.

Also, note that the data types INT(10) and VARCHAR do not actually exist in SQLite, although you can use them.
Instead you should use INTEGER and TEXT .