Use of Android SQLiteOpenHelper CRUD

Copy codeThe Code is as follows: public class DBOpenHelper extends SQLiteOpenHelper {
// The class is not instantiated and cannot be used as a parameter of the parent class constructor. It must be declared as static
Public DBOpenHelper (Context context, int version ){
Super (context, "SQLite. db", null, version );
// The third parameter CursorFactory specifies the factory class for obtaining a cursor instance during query execution. Setting null indicates that the default cursor factory is used;
}
@ Override
Public void onCreate (SQLiteDatabase db) {// called when the database was first created. The version number assigned when the database was first created is 0.
// SQLiteDatabase is used to generate database tables. database storage path: <package name>/databases/
Db.exe cSQL ("create table person (personid integer primary key autoincrement, name varchar (20 ))");
}
@ Override
Public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion) {// called when the version number is upgraded; it is not called if the database does not exist
Db.exe cSQL ("alter table person add phone varchar (12) null"); // add a column to the table
}
}
DBOpenHelper dbOpenHelper = new DBOpenHelper (getContext (), 1 );
DbOpenHelper. getWritableDatabase (); // create database table or open database table

Public class PersonService {
PrivateDBOpenHelperDbOpenHelper;
Public PersonService (Context context ){
Super ();
This. dbOpenHelper = new DBOpenHelper (context, 2 );
}
Public void save (Person person ){
SQLiteDatabase db = dbOpenHelper. getWritableDatabase ();
// SQLiteDatabase db2 = dbOpenHelper. getWritableDatabase (); With the cache function, the same Helper uses this method to get the object db;
Db.exe cSQL ("insert into person (name, phone) values (?,?) ", New Object [] {person. getName (), person. getPhone ()});
}
Public void delete (Integer id ){
SQLiteDatabase db = dbOpenHelper. getWritableDatabase ();
Db.exe cSQL ("delete from person where personid =? ", New Object [] {id });
}
Public void update (Person person ){
SQLiteDatabase db = dbOpenHelper. getWritableDatabase ();
Db.exe cSQL ("update person set name = ?, Phone =? Where personid =? ", New Object [] {person. getName (), person. getPhone (), person. getId ()});
}
Public Person find (Integer id ){
SQLiteDatabase db = dbOpenHelper. getReadableDatabase ();
// If the database disk space is not full, the obtained instance is the object obtained by getWritableDatabase (), because this method calls the getWritableDatabase method;
Cursor cursor = db. rawQuery ("select * from person where personid =? ", New String [] {id. toString ()});
If (cursor. moveToFirst ()){
Int personid = cursor. getInt (cursor. getColumnIndex ("personid "));
String name = cursor. getString (cursor. getColumnIndex ("name "));
String phone = cursor. getString (cursor. getColumnIndex ("phone "));
Return new Person (personid, name, phone );
}
Cursor. close ();
Return null;
}
/*
* Retrieve paging data
*/
Public List getScollData (int offest, int maxResult ){
List persons = new ArrayList ();
SQLiteDatabase db = dbOpenHelper. getReadableDatabase ();
Cursor cursor = db. rawQuery ("select * from person order by personid asc limit ?,? ", New String [] {String. valueOf (offest), String. valueOf (maxResult )});
While (cursor. moveToNext ()){
Int personid = cursor. getInt (cursor. getColumnIndex ("personid "));
String name = cursor. getString (cursor. getColumnIndex ("name "));
String phone = cursor. getString (cursor. getColumnIndex ("phone "));
Persons. add (new Person (personid, name, phone ));
}
Cursor. close ();
Return persons;
}
Public long getCount (){
SQLiteDatabase db = dbOpenHelper. getReadableDatabase ();
Cursor cursor = db. rawQuery ("select count (*) from person", null );
Cursor. moveToFirst ();
Long result = cursor. getLong (0 );
Return result;
}
}

Public class OtherPersonService {
PrivateDBOpenHelperDbOpenHelper;
Public OtherPersonService (Context context ){
Super ();
This. dbOpenHelper = new DBOpenHelper (context, 2 );
}
Public void save (Person person ){
SQLiteDatabase db = dbOpenHelper. getWritableDatabase ();
ContentValuesValues = new ContentValues (); // ContentValues is used to save the value of a field.
Values. put ("name", person. getName ());
Values. put ("phone", person. getPhone ());
Db. insert ("person", null, values); // The third parameter is the field value, and the second parameter is the null field. If the third parameter is null
}
Public void delete (Integer id ){
SQLiteDatabase db = dbOpenHelper. getWritableDatabase ();
Db. delete ("person", "personid =? ", New String [] {id. toString ()});
}
Public void update (Person person ){
SQLiteDatabase db = dbOpenHelper. getWritableDatabase ();
ContentValues values = new ContentValues ();
Values. put ("name", person. getName ());
Values. put ("phone", person. getPhone ());
Db. update ("person", values, "personid =? ", New String [] {person. getId (). toString ()});
}
Public Person find (Integer id ){
SQLiteDatabase db = dbOpenHelper. getReadableDatabase ();
Cursor cursor = db. query ("person", null, "personid =? ", New String [] {id. toString ()}, null );
If (cursor. moveToFirst ()){
Int personid = cursor. getInt (cursor. getColumnIndex ("personid "));
String name = cursor. getString (cursor. getColumnIndex ("name "));
String phone = cursor. getString (cursor. getColumnIndex ("phone "));
Return new Person (personid, name, phone );
}
Cursor. close ();
Return null;
}
/*
* Retrieve paging data
*/
Public List getScollData (int offest, int maxResult ){
List persons = new ArrayList ();
SQLiteDatabase db = dbOpenHelper. getReadableDatabase ();
Cursor cursor = db. query ("person", null, "personid asc", offest + "," + maxResult );
// Db. query (table, columns, selection, selectionArgs, groupBy, having, orderBy, limit );
While (cursor. moveToNext ()){
Int personid = cursor. getInt (cursor. getColumnIndex ("personid "));
String name = cursor. getString (cursor. getColumnIndex ("name "));
String phone = cursor. getString (cursor. getColumnIndex ("phone "));
Persons. add (new Person (personid, name, phone ));
}
Cursor. close ();
Return persons;
}
Public long getCount (){
SQLiteDatabase db = dbOpenHelper. getReadableDatabase ();
Cursor cursor = db. query ("person", new String [] {"count (*)"}, null, null );
// Db. query (table, columns, selection, selectionArgs, groupBy, having, orderBy );
Cursor. moveToFirst ();
Long result = cursor. getLong (0 );
Return result;
}
}