我需要创建一个方法,将数据添加到数据库,然后,微调器应该显示它。正如我测试,显示工作正常,但我不知道,我怎么能告诉数据库,我只想创建一些数据。例如,我有一个名为chestExercises的表,其中包含三列firstColumn,secondColumn,thirdColumn,它们具有以下值:
firstColumn = "exerciseOne"
secondColumn = "exerciseTwo"
thirdColumn = "exerciseThree"
现在,我希望程序只创建一次这些数据。正如我之前写的,我做了一些“测试”,数据库一直在创建这些数据,我不想有重复。那么..我怎么能“告诉”数据库,我想只做一次?
数据库
public databaseHelper(Context context) {
super(context, DATABASE_NAME, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT," + COLUMN_2 + " TEXT," + COLUMN_3 + " TEXT," + COLUMN_4 + " TEXT)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int i, int i1) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
public boolean insertData() {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(COLUMN_2, "1");
contentValues.put(COLUMN_3, "2");
contentValues.put(COLUMN_4, "3");
long result = db.insert(TABLE_NAME, null, contentValues);
if (result == -1) {
return false;
} else
return true;
}
public List<String> getAllLabels() {
List<String> labels = new ArrayList<String>();
String selectQuery = "SELECT * FROM " + TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do {
labels.add(cursor.getString(1));
labels.add(cursor.getString(2));
labels.add(cursor.getString(3));
} while (cursor.moveToNext());
}
cursor.close();
db.close();
return labels;
}
}
主要信息
public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {
Spinner spinner;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
spinner = (Spinner) findViewById(R.id.spinner);
databaseHelper db = new databaseHelper(getApplicationContext());
if (spinner == null){
db.insertData();
}else {
Toast.makeText(MainActivity.this,
"Your Message", Toast.LENGTH_LONG).show();
}
loadData();
}
public void loadData(){
databaseHelper db = new databaseHelper(getApplicationContext());
List<String> labels = db.getAllLabels();
ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, labels);
dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(dataAdapter);
}
@Override
public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
String label = adapterView.getItemAtPosition(i).toString();
Toast.makeText(adapterView.getContext(),"Selected: "+label,Toast.LENGTH_LONG).show();
}
@Override
public void onNothingSelected(AdapterView<?> adapterView) {
}
}
一种选择是定义表,以便组合3列形成UNIQUE约束,因此如果组合列存在则将导致冲突。
EG
db.execSQL("create table " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT," + COLUMN_2 + " TEXT," + COLUMN_3 + " TEXT," + COLUMN_4 + " TEXT, UNIQUE (" + COLUMN_2 + "," + COLUMN_3 + "," + COLUMN_4 + " ))");
在这种情况下,不会插入相同的值组合(因为insert
方法有效地使用INSERT或IGNORE,因此如果发生冲突,则忽略INSERT)。
另一种方法是通过检查行计数来检查表是否已有任何数据。
你可以在DatabaseHelper类中有一个方法,例如: -
public boolean isTableEmpty(String tablename) {
return DatabaseUtils.queryNumEntries(this.getWritableDatabase(),tablename) < 1;
}
public boolean insertDataCheckingForDuplicate(String value1, String value2, String value3) {
SQLiteDatabase db = this.getWritableDatabase();
int rowcount = 0;
String whereclause = COLUMN_2 + "=? AND " + COLUMN_3 + "=? AND " + COLUMN_4 + "=?";
String[] whereargs = new String[]{value1,value2,value3};
Cursor csr = db.query(TABLE_NAME,null,whereclause,whereargs,null,null,null);
rowcount = csr.getCount();
csr.close();
if (rowcount > 0) {
return false;
}
ContentValues contentValues = new ContentValues();
contentValues.put(COLUMN_2, value1);
contentValues.put(COLUMN_3, value2);
contentValues.put(COLUMN_4, value3);
long result = db.insert(TABLE_NAME, null, contentValues);
if (result == -1) {
return false;
} else
return true;
}
使用此方法,您可以提供预加载的数据库(即存在基础数据)。首次打开数据库时,数据库将放置在资产文件夹中,从资源文件夹复制到相关位置。该过程查看数据库是否存在,如果存在,则打开数据库,如果不存在,则复制数据库。
您可以使用SQLiteOpenAssethelper来简化此过程,请参阅android-sqlite-asset-helper。还有很多关于如何在StackOverflow上自己执行此操作的示例。