如何在Android中存储嵌套对象数据？[房间]
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"
}
]
}
]
}
解决方案
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
- 表_mydata，共2列(易于添加更多)
- 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)，
- Food_name(因为它在SQLite中是字符串，所以是文本类型)。
- 表_unit，共4列
- _unit(因为它在SQLite中是字符串，所以是文本类型)
- _Amount(因为它在SQLite中是浮点类型然后是REAL)
- _calory(因为它在SQLite中是浮点类型，则为REAL)
- parent_Food_id因为它是指Food_id是整数，那么它将是整数。
- 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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