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Android 下的 SQLite 操作封装:DatabaseUtil

Android 下的 SQLite 操作封装:DatabaseUtil

DatabaseUtil has private inner class DatabaseHelper, which is responsible for creating and updating database.

DatabaseUtil.java

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package com.dbexample;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DatabaseUtil{

private static final String TAG = "DatabaseUtil";

/**
* Database Name
*/
private static final String DATABASE_NAME = "student_database";

/**
* Database Version
*/
private static final int DATABASE_VERSION = 1;

/**
* Table Name
*/
private static final String DATABASE_TABLE = "tb_student";

/**
* Table columns
*/
public static final String KEY_NAME = "name";
public static final String KEY_GRADE = "grade";
public static final String KEY_ROWID = "_id";

/**
* Database creation sql statement
*/
private static final String CREATE_STUDENT_TABLE =
"create table " + DATABASE_TABLE + " (" + KEY_ROWID + " integer primary key autoincrement, "
+ KEY_NAME +" text not null, " + KEY_GRADE + " text not null);";

/**
* Context
*/
private final Context mCtx;

private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;

/**
* Inner private class. Database Helper class for creating and updating database.
*/
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
/**
* onCreate method is called for the 1st time when database doesn't exists.
*/
@Override
public void onCreate(SQLiteDatabase db) {
Log.i(TAG, "Creating DataBase: " + CREATE_STUDENT_TABLE);
db.execSQL(CREATE_STUDENT_TABLE);
}
/**
* onUpgrade method is called when database version changes.
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
+ newVersion);
}
}

/**
* Constructor - takes the context to allow the database to be
* opened/created
*
* @param ctx the Context within which to work
*/
public DatabaseUtil(Context ctx) {
this.mCtx = ctx;
}
/**
* This method is used for creating/opening connection
* @return instance of DatabaseUtil
* @throws SQLException
*/
public DatabaseUtil open() throws SQLException {
mDbHelper = new DatabaseHelper(mCtx);
mDb = mDbHelper.getWritableDatabase();
return this;
}
/**
* This method is used for closing the connection.
*/
public void close() {
mDbHelper.close();
}

/**
* This method is used to create/insert new record Student record.
* @param name
* @param grade
* @return long
*/
public long createStudent(String name, String grade) {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_NAME, name);
initialValues.put(KEY_GRADE, grade);
return mDb.insert(DATABASE_TABLE, null, initialValues);
}
/**
* This method will delete Student record.
* @param rowId
* @return boolean
*/
public boolean deleteStudent(long rowId) {
return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}

/**
* This method will return Cursor holding all the Student records.
* @return Cursor
*/
public Cursor fetchAllStudents() {
return mDb.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME,
KEY_GRADE}, null, null, null, null, null);
}

/**
* This method will return Cursor holding the specific Student record.
* @param id
* @return Cursor
* @throws SQLException
*/
public Cursor fetchStudent(long id) throws SQLException {
Cursor mCursor =
mDb.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
KEY_NAME, KEY_GRADE}, KEY_ROWID + "=" + id, null,
null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}

/**
* This method will update Student record.
* @param id
* @param name
* @param standard
* @return boolean
*/
public boolean updateStudent(int id, String name, String standard) {
ContentValues args = new ContentValues();
args.put(KEY_NAME, name);
args.put(KEY_GRADE, standard);
return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + id, null) > 0;
}
}

使用方法:

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//插入
DatabaseUtil dbUtil = new DatabaseUtil(this);
dbUtil.open();
dbUtil.createStudent("Prashant Thakkar", "10th");
dbUtil.close();

//查询
DatabaseUtil dbUtil = new DatabaseUtil(this);
dbUtil.open();
Cursor cursor = dbUtil.fetchAllStudents();
if(cursor != null){
while(cursor.moveToNext()){
Log.i("Student", "Student Name: " + cursor.getString(1) +
" Grade " + cursor.getString(2));
}
}
dbUtil.close();
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