SQLite with Foreign Key + Models Android Studio CRUD

Posted 2021-04-13

抱歉我的英文

我将构建一个简单的例子：

---

表T_User

id_user integer primary key autoincrement,

email_user text not null,

pass_user text not null,

id_person integer foreign key(id_person) references T_Person(id_person)

---

表T_Person

id_person integer primary key autoincrement,

name_person text not null,

cel_person text not null

---

android Studio：

user.Java

public static final String TAG = User.class.getSimpleName();

1）在这里我需要使用相同的表名？

public static final String TABLE = "T_User"; 

2）在这里我需要把我桌子的所有列？比如“id_user”

public static final int KEY_ID_USER = "id_user";
public static final String KEY_EMAIL_USER = "email_user";
public static final String KEY_PASS_USER= "pass_user";
public static final int KEY_ID_PERSON = "id_person";

private int id;
private String email;
private String pass;
private Person person;
//constructor
//getters & setters

user repo.Java

    public static String createTable(){
        return "CREATE TABLE " + User.TABLE  + "("
                + User.KEY_ID_USER + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + User.KEY_EMAIL_USER + " TEXT,"
                + User.KEY_PASS_USER + " TEXT,"
                + User.KEY_ID_PERSON  + " INTEGER)";
    }
    public void insert(User user) {
        SQLiteDatabase db = DatabaseManager.getInstance().openDatabase();
        ContentValues values = new ContentValues();

3）我不需要这条线吗？ （因为自动增量）

        values.put(User.KEY_ID_USER, user.getId());


        values.put(User.KEY_EMAIL_USER, user.getEmail());
        values.put(User.KEY_PASS_USER, user.getPass());

4）这就是我从人那里得到的身份？

        values.put(User.KEY_ID_PERSON , user.person.getId());


        db.insert(User.TABLE, null, values);
        DatabaseManager.getInstance().closeDatabase();
    }

5）如何进行更新和选择

答案

这是一个基于您的设计的工作示例，包含更新和选择方法。

它由2个java类和调用活动MainActivity.java以及SQLiteOpenHelper类的子类组成，通常称为DBHelper，因此它是DBHelper.java

DBHelper.java

public class DBHelper extends SQLiteOpenHelper {

    public static final String DBNAME = "mydb";
    public static final int DBVERSION = 1;

    public static final String TB_USER = "T_User";
    public static final String TB_PERSON = "T_Person";

    public static final String COl_USER_ID = BaseColumns._ID;
    public static final String COl_USER_EMAIL = "email_user";
    public static final String COL_USER_PASS = "pass_user";
    public static final String COl_USER_PERSON = "id_person";

    public static final String COL_PERSON_ID = BaseColumns._ID;
    public static final String COl_PERSON_NAME = "name_person";
    public static final String COL_PERSON_CEL = "cel_person";

    SQLiteDatabase mDB;
    public DBHelper(Context context) {
        super(context, DBNAME, null, DBVERSION);
        mDB  = this.getWritableDatabase();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String crtpersonsql = "CREATE TABLE IF NOT EXISTS " + TB_PERSON + "(" +
                COL_PERSON_ID + " INTEGER PRIMARY KEY, " +
                COl_PERSON_NAME + " TEXT NOT NULL," +
                COL_PERSON_CEL + " TEXT NOT NULL " +
                ")";
        String crtusersql = "CREATE TABLE If NOT EXISTS " + TB_USER + "(" +
                COl_USER_ID + " INTEGER PRIMARY KEY, " +
                COl_USER_EMAIL + " TEXT NOT NULL, " + //perhaps make unique
                COL_USER_PASS + " TEXT NOT NULL, " +
                COl_USER_PERSON + " INTEGER REFERENCES " + TB_PERSON + "(" +
                COL_PERSON_ID +
                ")" +
                ")";
        db.execSQL(crtpersonsql);
        db.execSQL(crtusersql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {

    }

    public long insertPerson(String name, String cel) {
        ContentValues cv = new ContentValues();
        cv.put(COl_PERSON_NAME,name);
        cv.put(COL_PERSON_CEL,cel);
        return mDB.insert(TB_PERSON,null,cv);
    }

    public long insertUser(String email, String pass, long personid) {
        ContentValues cv = new ContentValues();
        cv.put(COl_USER_EMAIL,email);
        cv.put(COL_USER_PASS,pass);
        cv.put(COl_USER_PERSON,personid);
        return mDB.insert(TB_USER,null,cv);
    }

    public Cursor getAllPersons() {
        return mDB.query(TB_PERSON,null,null,null,null,null,null);
    }

    public Cursor getAllUsers() {
        return mDB.query(TB_USER,null,null,null,null,null,null);
    }

    public Cursor getAllPersonsAndTheReferencedUser() {
        String table = TB_PERSON +
                " JOIN " + TB_USER +
                " ON " + COl_USER_PERSON + "=" +
                TB_PERSON + "." + COL_PERSON_ID;
        String[] columns = new String[]{
                TB_PERSON + "." + COL_PERSON_ID + " AS " + TB_PERSON + "_" + COL_PERSON_ID,
                COl_PERSON_NAME,
                COL_PERSON_CEL,
                TB_USER + "." + COl_USER_ID + " AS " + TB_USER + "_" + COl_USER_ID,
                COl_USER_EMAIL,
                COL_USER_PASS
        };
        Log.d("GETALLPandU","Table (FROM) clause = " + table);
        return mDB.query(table,columns,null,null,null,null,null);
    }

    public int changePersonsName(long personid, String newname) {
        ContentValues cv = new ContentValues();
        cv.put(COl_PERSON_NAME,newname);
        String whereclause = COL_PERSON_ID + "=?";
        String[] whereargs = new String[]{String.valueOf(personid)};
        return mDB.update(TB_PERSON,cv,whereclause,whereargs);
    }

    public int changePersonsCel(long personid, String newcel) {
        ContentValues cv = new ContentValues();
        cv.put(COL_PERSON_CEL,newcel);
        String whereclause = COL_PERSON_ID + "=?";
        String[] whereargs = new String[]{String.valueOf(personid)};
        return mDB.update(TB_PERSON,cv,whereclause,whereargs);
    }
}

• 方法insertPerson用于向T_Person表添加行。
• 方法insertUser用于向T_User表添加行，注意personid（第3个参数）必须引用Person。
• 方法getAllPersons获取T_Person表中的所有行。
• 方法getAllUsers从T_User表中获取所有行。
• 方法getAllPersonsAndTheReferencedUser根据外键/引用从Person和User表中获取所有行。
• 方法changePersonsName允许根据人员的ID更新Person的名称。
• 方法changePersonscel允许根据人的id更新Person的cel。

MainActivity.java

public class MainActivity extends AppCompatActivity {

    DBHelper mDBHlpr;

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

        mDBHlpr = new DBHelper(this);

        // Delete all rows from both tables (if any)
        mDBHlpr.getWritableDatabase().delete(DBHelper.TB_USER,null,null);
        mDBHlpr.getWritableDatabase().delete(DBHelper.TB_PERSON,null,null);

        // Add some person rows
        mDBHlpr.insertPerson("Fred","0000-000-000"); // id will virtually certainly be 1
        mDBHlpr.insertPerson("Bert", "1111-111-111"); // id likely 2
        mDBHlpr.insertPerson("Mary","2222-222-222"); // id likely 3

        // Add some user rows
        mDBHlpr.insertUser("[e-mail]","Fred1234567890",1);
        mDBHlpr.insertUser("[e-mail]","Bert1234567890",2);
        mDBHlpr.insertUser("[e-mail]","Mary1234567890",3);

        //ooops add some unanticipated rows
        mDBHlpr.insertUser("[e-mail]","xxxx",3);
        mDBHlpr.insertUser("[e-mail]","xxxx",3);

        // Make some changes (updates)
        mDBHlpr.changePersonsCel(3,"6666-666-66");
        mDBHlpr.changePersonsName(3,"Marian");

        // get some data
        Cursor crs1 = mDBHlpr.getAllPersons();
        Cursor csr2 = mDBHlpr.getAllUsers();
        Cursor csr3 = mDBHlpr.getAllPersonsAndTheReferencedUser();

        // Output the retrieved data
        DatabaseUtils.dumpCursor(crs1);
        DatabaseUtils.dumpCursor(csr2);
        DatabaseUtils.dumpCursor(csr3);

        // Close the Cursors (should always be done when finished with the Cursor)
        crs1.close();
        crs1.close();
        csr3.close();
    }
}

这将调用DBHelper中的方法。

• 首先，实例化DBHelper的一个实例（mDBHlpr）。
• 接下来从两个表中删除所有行（如果有的话）（这样做是为了使App的结果一致）。
• 接下来添加一些人员和用户（包括一些意外/意外用户（结果是3个用户引用了人员3））。
• 然后做出一些改变（玛丽改为玛丽安，玛丽（玛丽安）玛丽从2222-222-222改为6666-666-66）。
• 运行所有三个选择方法（getAll ....）并创建3个Cursors。
• 游标被转储（写入日志）。
• 游标已关闭。

3项产出是： -

The Person table (3 rows) :-

>>>>> Dumping cursor android.database.sqlite.SQLiteCursor@a98de41
09-01 21:48:52.535 1919-1919/so52115977.so52115977 I/System.out: 0 {
       _id=1
09-01 21:48:52.536 1919-1919/so52115977.so52115977 I/System.out:    name_person=Fred
       cel_person=0000-000-000
    }
    1 {
       _id=2
       name_person=Bert
       cel_person=1111-111-111
    }
    2 {
       _id=3
       name_person=Marian
       cel_person=6666-666-66
    }
<<<<<

The User table (5 rows)

    >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@e149fe6
    0 {
       _id=1
       email_user=[e-mail]
       pass_user=Fred1234567890
       id_person=1
    }
    1 {
       _id=2
       email_user=[e-mail]
       pass_user=Bert1234567890
       id_person=2
    }
    2 {
       _id=3
       email_user=[e-mail]
       pass_user=Mary1234567890
09-01 21:48:52.537 1919-1919/so52115977.so52115977 I/System.out:    id_person=3
    }
    3 {
       _id=4
       email_user=[e-mail]
       pass_user=xxxx
       id_person=3
    }
    4 {
       _id=5
       email_user=[e-mail]
       pass_user=xxxx
       id_person=3
    }
    <<<<<

The linked/referenced/joined (Foreign Keyed) Person/User tables (5 rows)

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