java - 如何在 SQLite 中使用外键插入值？

Question

我是 Android Sqlite 数据库的新手。我在Android中使用SQLite创建了一个数据库，并且有一个表Student_details，它使用表的外键:Student，我已将id设置为AUTOINCRMENT 。我尝试从 Student 表返回AUTOINCRMENT Id 的值。

但我坚持使用返回值作为外键值插入COLUMN_FR_KEY_USER_ID = "student_id";。

如何使用 ContentValues 将另一个表中的外键值添加到 insetDataIntoStudentDetails 方法中？

DatabaseHelper.java

public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "finalStudent.db";
    private static final int VERSION_NUMBER = 16;
    private static final String TABLE_STUDENT = "Student";
    private static final String TABLE_DETAILS_NAME = "Student_details";

    private static final String COLUMN_STUDENT_ID = "id";
    private static final String COLUMN_DETAILS_ID = "id";
    private static final String COLUMN_FR_KEY_USER_ID = "student_id";
    private static final String COLUMN_STUDENT_NAME = "name";
    private static final String COLUMN_DETAILS_NAME = "name";
    private static final String COLUMN_STUDENT_EMAIL = "email";
    private static final String COLUMN_STUDENT_PASSWORD = "password";

    private static final String CREATE_STUDENT_TABLE = "CREATE TABLE "+TABLE_STUDENT+"( "+COLUMN_STUDENT_ID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+COLUMN_STUDENT_NAME+" TEXT, "+COLUMN_STUDENT_EMAIL+" TEXT, "+COLUMN_STUDENT_PASSWORD+" TEXT)";
    private static final String CREATE_DETAILS_TABLE = "CREATE TABLE "+TABLE_DETAILS_NAME+"( "+COLUMN_DETAILS_ID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+COLUMN_DETAILS_NAME+" TEXT, "+COLUMN_FR_KEY_USER_ID+" INTEGER, FOREIGN KEY("+COLUMN_FR_KEY_USER_ID+") REFERENCES "+TABLE_STUDENT+" ("+COLUMN_STUDENT_ID+") ON UPDATE CASCADE ON DELETE CASCADE)";

    private Context context;
    private static final String DROP_TABLE = "DROP TABLE IF EXISTS "+TABLE_STUDENT;
    private static final String DROP_DETAILS_TABLE = "DROP TABLE IF EXISTS "+TABLE_DETAILS_NAME;


    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, VERSION_NUMBER);
        this.context = context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        try {
            Toast.makeText(context,"Table created successfully and called onCreate method",Toast.LENGTH_SHORT).show();
            db.execSQL(CREATE_STUDENT_TABLE);
            db.execSQL(CREATE_DETAILS_TABLE);
        }catch (Exception e){
            Toast.makeText(context,"Exception : "+e,Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        try {

            Toast.makeText(context,"Table created successfully and called onCreate method",Toast.LENGTH_SHORT).show();
            db.execSQL(DROP_TABLE);
            db.execSQL(DROP_DETAILS_TABLE);
            onCreate(db);
        }catch (Exception e){
            Toast.makeText(context,"Exception : "+e,Toast.LENGTH_SHORT).show();
        }

    }

    public long insertDataIntoStudent( String name, String email, String password){
        // to write or read data in database , we have to call getWritableDatabase
        SQLiteDatabase sqLiteDatabase = this.getWritableDatabase();
        // we have to call contentValues class to store data in the data

        ContentValues contentValues = new ContentValues();
        contentValues.put(COLUMN_STUDENT_NAME,name);
        contentValues.put(COLUMN_STUDENT_EMAIL,email);
        contentValues.put(COLUMN_STUDENT_PASSWORD,password);

        // Insert the new row, returning the primary key value of the new row
        long newRowId = sqLiteDatabase.insert(TABLE_STUDENT,null,contentValues);
        return newRowId;
    }


    public void insetDataIntoStudentDetails(String name){

        SQLiteDatabase sqLiteDatabase = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
       // TODO: insert the foreign key's value 
        contentValues.put(name,name);
    }


    @Override
    public void onOpen(SQLiteDatabase db) {
        super.onOpen(db);
        //enable foreign key constraints like ON UPDATE CASCADE, ON DELETE CASCADE
        db.execSQL("PRAGMA foreign_keys=ON;");
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private final AppCompatActivity activity = MainActivity.this;
    DatabaseHelper databaseHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        databaseHelper = new DatabaseHelper(activity);
        databaseHelper.insertDataIntoStudent("Bappy","abcd@gmail.com","145456");
    }
    }

Answer 1

我将回答有关数据库的一般问题，而不是专门讨论 Sqlite 或其在 Android 中的用法。

因此，您有学生的姓名(不是主键)，但您需要将该学生的一些附加数据保存到另一个表中。步骤是:

1. 执行 SELECT id FROM Students WHERE name = ? 以查找相关标识符。
2. 使用检索到的 id 作为键，对辅助表执行 INSERT INTO Student_details。

额外提示:

1. 名称不是一个好的唯一标识符。多定义一个标准是件好事 - 例如群组名称、群组编号甚至出生日期。
2. 当您的数据库足够大时，您可能会受益于搜索条件的索引来优化第一个查询的执行。但客户端(应用内)数据库通常并非如此。
3. 这里我们假设 name 不是可以在搜索 id 和执行 INSERT 之间被其他人(或其他东西)更新的数据。否则，明智的做法是使用事务并“锁定”您的学生，直到您完成更新。