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如何在Android中存储嵌套对象数据？[房间]

Java问题
2022-01-01

How can I store data with nested object data in Android? [Room](如何在Android中存储嵌套对象数据？[房间])

本文介绍了如何在Android中存储嵌套对象数据？[房间]的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我有一个高维数据集，它提供了一个json结构(大约3000个对象，每个对象的数组和该数组中的数十个对象)。我在排球图书馆的帮助下阅读了它们。我想保存此数据。存储在数据库中，并且可以轻松地访问它。我如何才能做到这一点

我找不到房间的示例

JSON数据

{
"MyData": [
 {
   "food_id": "1",
   "food_name": "Food 1",
   "food_image": "imageurl",
   "food_kcal": "32",
   "food_url": "url",
   "food_description": "desc",
   "carb_percent": "72",
   "protein_percent": "23",
   "fat_percent": "4",
   "units": [
     {
       "unit": "Unit A",
       "amount": "735.00",
       "calory": "75.757",
       "calcium": "8.580",
       "carbohydrt": "63.363",
       "cholestrl": "63.0",
       "fiber_td": "56.12",
       "iron": "13.0474",
       "lipid_tot": "13.01",
       "potassium": "11.852",
       "protein": "717.1925",
       "sodium": "112.02",
       "vit_a_iu": "110.7692",
       "vit_c": "110.744"
     },
     {
       "unit": "Unit C",
       "amount": "32.00",
       "calory": "23.757",
       "calcium": "53.580",
       "carbohydrt": "39.363",
       "cholestrl": "39.0",
       "fiber_td": "93.12",
       "iron": "93.0474",
       "lipid_tot": "93.01",
       "potassium": "9.852",
       "protein": "72.1925",
       "sodium": "10.0882",
       "vit_a_iu": "80.7692",
       "vit_c": "80.744"
     }
   ]
 },
 {
   "food_id": "2",
   "food_name": "Food 2",
   "food_image": "imageurl",
   "food_kcal": "50",
   "food_url": "url",
   "food_description": "desc",
   "carb_percent": "25",
   "protein_percent": "14",
   "fat_percent": "8",
   "units": [
     {
       "unit": "Unit A",
       "amount": "25.00",
       "calory": "25.757",
       "calcium": "55.580",
       "carbohydrt": "53.363",
       "cholestrl": "53.0",
       "fiber_td": "53.12",
       "iron": "53.0474",
       "lipid_tot": "53.01",
       "potassium": "17.852",
       "protein": "757.1925",
       "sodium": "122.02",
       "vit_a_iu": "10.7692",
       "vit_c": "10.744"
     },
     {
       "unit": "Unit C",
       "amount": "2.00",
       "calory": "2.757",
       "calcium": "5.580",
       "carbohydrt": "3.363",
       "cholestrl": "3.0",
       "fiber_td": "3.12",
       "iron": "3.0474",
       "lipid_tot": "3.01",
       "potassium": "77.852",
       "protein": "77.1925",
       "sodium": "12.02",
       "vit_a_iu": "0.7692",
       "vit_c": "0.744"
     },
     {
       "unit": "Unit G",
       "amount": "1.00",
       "calory": "2.1",
       "calcium": "0.580",
       "carbohydrt": "0.363",
       "cholestrl": "0.0",
       "fiber_td": "0.12",
       "iron": "0.0474",
       "lipid_tot": "0.01",
       "potassium": "5.852",
       "protein": "0.1925",
       "sodium": "1.02",
       "vit_a_iu": "0.7692",
       "vit_c": "0.744"
     }
   ]
 }
]
}

推荐答案

对于SQLite

您必须做的第一件事是确定数据库的架构。

查看数据时，您有许多MyData对象，每个对象将有0个或更多个Unit对象。

因此，您可以有一个用于MyData对象的表和一个用于Unit对象的表。每个Unit都将有一个父MyData对象。因此，除了每个单元的数据之外，您还可以有一个引用(映射、关联)MyData的列(很可能是Food_id，假设这唯一地标识了MyData)。

使用MyData的简写版本(只有Food_id、Food_name)和Unit的简写版本(单位、金额和卡路里)来演示，那么您可以有两个类，如下所示：-

class MyData {
    public static final String TABLE_NAME = "_mydata";
    public static final String COLUMN_FOOD_ID = "_food_id";
    public static final String COLUMN_FOOD_NAME = "_food_name";
    long food_id;
    String food_name;
    Unit[] units;

    public MyData(long food_id, String food_name, Unit[] units) {
        this.food_id = food_id;
        this.food_name = food_name;
        this.units = units;
    }
}

和

class Unit {
    public static final String TABLE_NAME = "_unit";
    public static final String COLUMN_UNIT = "_unit";
    public static final String COLUMN_AMOUNT = "_amount";
    public static final String COLUMN_CALORY = "_calory";
    public static final String COLUMN_FOOD_ID_PARENT ="parent_food_id";
    String unit;
    double amount;
    double calory;

    public Unit(String unit, double amount, double calory) {
        this.unit = unit;
        this.amount = amount;
        this.calory = calory;
    }
}
请注意将用于表的常量，即模式。为简洁起见，这些代码放在类中，它们可以在其他地方编码。

请注意附加列parent_Food_id，它将用于引用父Food_id。

因此架构可能看起来像

  1. 表_mydata，共2列(易于添加更多)
    1. Food_id(将是唯一的(主键)，如果值是整数，则为整数类型，如果是SQLite，则为整数类型)，
    2. Food_name(因为它在SQLite中是字符串，所以是文本类型)。
  2. 表_unit，共4列
    1. _unit(因为它在SQLite中是字符串，所以是文本类型)
    2. _Amount(因为它在SQLite中是浮点类型然后是REAL)
    3. _calory(因为它在SQLite中是浮点类型，则为REAL)
    4. parent_Food_id因为它是指Food_id是整数，那么它将是整数。
      1. 因为它创建了两个表之间的关系，所以应该要求它确实引用了Food_id。虽然不是必需的，但最好是强制引用的完整性(引用完整性)，为此可以添加外键约束。
    • 拥有主键始终是明智的，但由于其他MyData对象的单位和/或金额和/或卡路里可能具有相同的值，这三个值的组合可能不太可能相同。因此，主键全部为3列。

在SQLite术语中，将创建上述内容的SQL(每个表一个)可以是：-

  • CREATE TABLE _mydata(_food_id INTEGER PRIMARY KEY,_food_name TEXT)和
  • CREATE TABLE _unit(_unit TEXT,_amount REAL,_calory REAL,parent_food_id INTEGER REFERENCES _mydata(_food_id) ON DELETE CASCADE ON UPDATE CASCADE, PRIMARY KEY(_unit,_amount,_calory))

处理数据库

对于Android和SQLite，典型的方法是使用扩展SQLiteOpenHelper的DatabaseHelper。SQLiteOpenHelpr需要2个重写方法onCreate和onUpgrae

  • onCreate在创建数据库时运行。
    • 它只在存在持久存在的数据库时运行一次，即它只在应用程序第一次运行时运行。
    • 此方法通常用于定义实体/组件，如表。
  • 传递给SQLiteOpenHelper的数据库版本的onUpgrade运行大于从数据库本身提取的版本号。

通常用于访问数据库的代码，如添加、删除、更新、删除或提取数据。

对于演示，数据库将只有用于将数据插入到表中的方法。此外，将采用JSON字符串(相当于文件)并填充表的方法。

因此DatabaseHelper类可以是：-

class DatabaseHelper extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "my_database.db";
    public static final int DATABASE_VERSION = 1;

    private SQLiteDatabase db;
    private static volatile DatabaseHelper instance = null;
    private DatabaseHelper(Context context) {
        super(context,DATABASE_NAME,null,DATABASE_VERSION);
        db = this.getWritableDatabase();
    }

    /* Use a singleton approach */
    public static DatabaseHelper getInstance(Context context) {
        if (instance == null) {
            instance = new DatabaseHelper(context);
        }
        return instance;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(
                "CREATE TABLE IF NOT EXISTS " + MyData.TABLE_NAME + "(" +
                        MyData.COLUMN_FOOD_ID + " INTEGER PRIMARY KEY," +
                        MyData.COLUMN_FOOD_NAME + " TEXT" +
                        ")"
        );

        db.execSQL(
                "CREATE TABLE IF NOT EXISTS " + Unit.TABLE_NAME + "(" +
                        Unit.COLUMN_UNIT + " TEXT," +
                        Unit.COLUMN_AMOUNT + " REAL," +
                        Unit.COLUMN_CALORY + " REAL," +
                        Unit.COLUMN_FOOD_ID_PARENT +
                        /* Foreign Key Constraint to enforce referential integrity*/
                        " INTEGER REFERENCES " + MyData.TABLE_NAME + "(" + MyData.COLUMN_FOOD_ID + ") " +
                        /* These make maintaining referential integrity easier */
                        "ON DELETE CASCADE " +
                        "ON UPDATE CASCADE, " +
                        /* define the primary key */
                        " PRIMARY KEY(" +
                        Unit.COLUMN_UNIT + "," + Unit.COLUMN_AMOUNT + "," + Unit.COLUMN_CALORY +
                        ")" +
                        ")"
        );

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {
        /* not expecting to increase the database version so leave this to do nothing */
    }

    public long insertMyData(MyData myData) {
        ContentValues cv = new ContentValues();
        cv.put(MyData.COLUMN_FOOD_ID,myData.food_id);
        cv.put(MyData.COLUMN_FOOD_NAME,myData.food_name);
        return db.insert(MyData.TABLE_NAME,null,cv);
    }

    public long insertUnit(Unit unit, long parentId) {
        ContentValues cv = new ContentValues();
        cv.put(Unit.COLUMN_UNIT,unit.unit);
        cv.put(Unit.COLUMN_AMOUNT,unit.amount);
        cv.put(Unit.COLUMN_CALORY,unit.calory);
        cv.put(Unit.COLUMN_FOOD_ID_PARENT,parentId);
        return db.insert(Unit.TABLE_NAME,null,cv);
    }

    public void massInsert(String jsonString) {
        MyData[] extracted = new Gson().fromJson(jsonString,MyData[].class);
        db.beginTransaction();
        for(MyData m: new Gson().fromJson(jsonString,MyData[].class)) {
            long food_id = insertMyData(m);
            if (food_id > 0) {
                for(Unit u: m.units) {
                    insertUnit(u,food_id);
                }
            }
        }
        db.setTransactionSuccessful();
        db.endTransaction();
    }
}

演示

以下是在活动中使用上述内容的演示，即MainActivity：-

public class MainActivity extends AppCompatActivity {

    MyData[] TESTDATA = {
            new MyData(
                    1,
                    "Bat",
                    new Unit[]{
                            new Unit("Unit A",15.0000,32.4877372383),
                            new Unit("Unit C",110.0000,238.243404414),
                            new Unit("Unit F",1.0000,2.16584914922)
                    }
                    ),
            new MyData(
                    2,
                    "Another",
                    new Unit[]{
                            new Unit("Unit A",17.0000,3.4877372383),
                            new Unit("Unit C",10.0000,382.243404414),
                            new Unit("Unit F",3.0000,5.16584914922)
                    }
            ),
    };

    DatabaseHelper dbHelper;

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

        String test = new Gson().toJson(TESTDATA);
        Log.d("APPINFO","TESTDATA as JSON is
	" + test);
        //MyData[] extracted = new Gson().fromJson(test,MyData[].class);

        dbHelper = DatabaseHelper.getInstance(this); // Prepare to use the database
        dbHelper.massInsert(test); // Actually use the database to insert the data

        /* Example of extracting data using a JOIN to combine the MyData and the related Units */
        Cursor csr =  dbHelper.getWritableDatabase().query(
                MyData.TABLE_NAME + " JOIN " + Unit.TABLE_NAME + " ON " + Unit.COLUMN_FOOD_ID_PARENT + "=" + MyData.COLUMN_FOOD_ID,
                null,null,null,null,null,null
                );
        DatabaseUtils.dumpCursor(csr);
        csr.close();

    }
}

结果

运行时日志包括：-

2022-01-08 07:32:14.666  D/APPINFO: TESTDATA as JSON is
        [{"food_id":1,"food_name":"Bat","units":[{"amount":15.0,"calory":32.4877372383,"unit":"Unit A"},{"amount":110.0,"calory":238.243404414,"unit":"Unit C"},{"amount":1.0,"calory":2.16584914922,"unit":"Unit F"}]},{"food_id":2,"food_name":"Another","units":[{"amount":17.0,"calory":3.4877372383,"unit":"Unit A"},{"amount":10.0,"calory":382.243404414,"unit":"Unit C"},{"amount":3.0,"calory":5.16584914922,"unit":"Unit F"}]}]

和

2022-01-08 07:32:14.698  I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@f302fce
2022-01-08 07:32:14.699  I/System.out: 0 {
2022-01-08 07:32:14.699  I/System.out:    _food_id=1
2022-01-08 07:32:14.699  I/System.out:    _food_name=Bat
2022-01-08 07:32:14.699  I/System.out:    _unit=Unit A
2022-01-08 07:32:14.699  I/System.out:    _amount=15
2022-01-08 07:32:14.699  I/System.out:    _calory=32.4877
2022-01-08 07:32:14.699  I/System.out:    parent_food_id=1
2022-01-08 07:32:14.699  I/System.out: }
2022-01-08 07:32:14.699  I/System.out: 1 {
2022-01-08 07:32:14.699  I/System.out:    _food_id=1
2022-01-08 07:32:14.699  I/System.out:    _food_name=Bat
2022-01-08 07:32:14.700  I/System.out:    _unit=Unit C
2022-01-08 07:32:14.701  I/System.out:    _amount=110
2022-01-08 07:32:14.701  I/System.out:    _calory=238.243
2022-01-08 07:32:14.701  I/System.out:    parent_food_id=1
2022-01-08 07:32:14.701  I/System.out: }
2022-01-08 07:32:14.701  I/System.out: 2 {
2022-01-08 07:32:14.701  I/System.out:    _food_id=1
2022-01-08 07:32:14.701  I/System.out:    _food_name=Bat
2022-01-08 07:32:14.701  I/System.out:    _unit=Unit F
2022-01-08 07:32:14.701  I/System.out:    _amount=1
2022-01-08 07:32:14.701  I/System.out:    _calory=2.16585
2022-01-08 07:32:14.701  I/System.out:    parent_food_id=1
2022-01-08 07:32:14.701  I/System.out: }
2022-01-08 07:32:14.702  I/System.out: 3 {
2022-01-08 07:32:14.702  I/System.out:    _food_id=2
2022-01-08 07:32:14.702  I/System.out:    _food_name=Another
2022-01-08 07:32:14.702  I/System.out:    _unit=Unit A
2022-01-08 07:32:14.702  I/System.out:    _amount=17
2022-01-08 07:32:14.702  I/System.out:    _calory=3.48774
2022-01-08 07:32:14.702  I/System.out:    parent_food_id=2
2022-01-08 07:32:14.702  I/System.out: }
2022-01-08 07:32:14.702  I/System.out: 4 {
2022-01-08 07:32:14.702  I/System.out:    _food_id=2
2022-01-08 07:32:14.703  I/System.out:    _food_name=Another
2022-01-08 07:32:14.703  I/System.out:    _unit=Unit C
2022-01-08 07:32:14.703  I/System.out:    _amount=10
2022-01-08 07:32:14.703  I/System.out:    _calory=382.243
2022-01-08 07:32:14.703  I/System.out:    parent_food_id=2
2022-01-08 07:32:14.703  I/System.out: }
2022-01-08 07:32:14.703  I/System.out: 5 {
2022-01-08 07:32:14.703  I/System.out:    _food_id=2
2022-01-08 07:32:14.703  I/System.out:    _food_name=Another
2022-01-08 07:32:14.703  I/System.out:    _unit=Unit F
2022-01-08 07:32:14.703  I/System.out:    _amount=3
2022-01-08 07:32:14.704  I/System.out:    _calory=5.16585
2022-01-08 07:32:14.704  I/System.out:    parent_food_id=2
2022-01-08 07:32:14.704  I/System.out: }
2022-01-08 07:32:14.704  I/System.out: <<<<<

使用Android Studio的App Review数据库如下：-

和

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