Sqlite輕量級數據庫管理類·SQLite輕量級數據庫

很多時候，都要用到數據庫，爲了方便有效的使用數據庫，選擇建立一個數據庫管理類是一個很明智的選擇

這裏已Android的SQLite爲例

package czhy.grey.sun.exam.bin.manager_;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Environment;

import czhy.grey.sun.exam.bin.question_.Question;
import czhy.grey.sun.exam.bin.question_.QuestionExtra;

import java.io.File;

public class DBManager{
 private static final String DB_NAME = "exam_db.db"; //保存的數據庫文件名
 private static final String PACKAGE_NAME = "czhy.grey.sun.exam";
 private static final String DB_PATH = "/data" + Environment.getDataDirectory().getAbsolutePath() + "/" + PACKAGE_NAME; //在手機裏存放數據庫的位置
 private static final String DB_FILE = DB_PATH + "/" + DB_NAME;

private static SQLiteDatabase database;

public DBManager() {
 onCreate();
 }

private static void onCreate() {
 if (!(new File(DB_FILE).exists())) {//判斷數據庫文件是否存在，若不存在則新建(執行導入)，否則跳過
 /* 導入已有數據庫
 InputStream is = context.getAssets().open(DB_NAME); //欲導入的數據庫
 FileOutputStream fos = new FileOutputStream(DB_FILE);
 byte[] buffer = new byte[BUFFER_SIZE];
 int count;
 while ((count = is.read(buffer)) > 0) {
 fos.write(buffer, 0, count);
 }
 fos.close();
 is.close();
 */
 database = SQLiteDatabase.openOrCreateDatabase(DB_FILE,null);
 database.execSQL("CREATE TABLE [Type_](" +
 " [type_code] INTEGER PRIMARY KEY AUTOINCREMENT," +
 " [type_name] VARCHAR(50) NOT NULL)");
 database.execSQL("CREATE TABLE [Subject_](" +
 " [subject_code] VARCHAR(5) PRIMARY KEY," +
 " [subject_name] VARCHAR(50) NOT NULL," +
 " [subject_count] INTEGER NOT NULL DEFAULT 0)");
 database.execSQL("CREATE TABLE [Data_](" +
 " [data_subject] VARCHAR(5) NOT NULL REFERENCES [Subject_]([subject_code]) ON DELETE CASCADE ON UPDATE CASCADE," +
 " [data_code] INTEGER PRIMARY KEY AUTOINCREMENT, " +
 " [data_question] TEXT NOT NULL," +
 " [data_keys] VARCHAR(10) NOT NULL," +
 " [data_type] INTEGER NOT NULL REFERENCES [Type_]([type_code]) ON DELETE CASCADE ON UPDATE CASCADE)");
 database.execSQL("CREATE TABLE [Extra_](" +
 " [extra_code] VARCHAR NOT NULL," +
 " [extra_text] TEXT NOT NULL," +
 " [extra_data] INTEGER NOT NULL REFERENCES [Data_]([data_code]) ON DELETE CASCADE ON UPDATE CASCADE)");
 database.execSQL("CREATE TABLE [Wrong_](" +
 " [wrong_data] INTEGER NOT NULL REFERENCES [Data_]([data_code]) ON DELETE CASCADE ON UPDATE CASCADE)");
 database.execSQL("INSERT INTO [Type_] ([type_code],[type_name]) VALUES (1000101,'單選題')");
 database.execSQL("INSERT INTO [Type_] ([type_code],[type_name]) VALUES (1000102,'多選題')");
 database.execSQL("INSERT INTO [Type_] ([type_code],[type_name]) VALUES (1000103,'判斷題')");
 database.execSQL("INSERT INTO [Type_] ([type_code],[type_name]) VALUES (1000104,'辨析題')");
 database.execSQL("INSERT INTO [Type_] ([type_code],[type_name]) VALUES (1000105,'填空題')");
 database.execSQL("INSERT INTO [Type_] ([type_code],[type_name]) VALUES (1000106,'計算題')");
 database.execSQL("INSERT INTO [Type_] ([type_code],[type_name]) VALUES (1000107,'應用題')");
 database.execSQL("INSERT INTO [Type_] ([type_code],[type_name]) VALUES (1000108,'思考題')");
 database.close();
 }
 }

public static void OpenDatabase() {
 database = SQLiteDatabase.openOrCreateDatabase(DB_FILE,null);
 }

public static String Clear(){
 String str;

try {
 database.execSQL("delete from [Data_]");
 database.execSQL("delete from [Extra_]");
 database.execSQL("delete from [Subject_]");
 database.execSQL("update [sqlite_sequence] SET [seq] = 0 where [name] = 'Data_'");

return null;
 }catch (Exception e){
 str = e.getMessage();
 }

return str;
 }

public static void CloseDatabase() {
 database.close();
 }

/**
 * 插入
 * @param question 題目信息
 */
 public static void Insert(Question question){
 String sql = "select [subject_count] from [Subject_] where [subject_code] = '"+question.getCode()+"'";
 Cursor cursor = database.rawQuery(sql,null);
 cursor.moveToNext();
 int count = cursor.getInt(0);
 cursor.close();

//插入題目基本信息
 sql = "insert into [Data_] ([data_subject],[data_question],[data_type],[data_keys]) values (?,?,?,?)";
 database.execSQL(sql,new String[]{question.getCode(),question.getQuestion(),""+ STManger.GetTypeCode(question.getType()),question.getKeys()});
 //插入額外信息 如：選擇題選項，問答題詳細答案
 if(question.getExtra()!=null && !question.getExtra().isEmpty()){
 cursor = database.rawQuery("select last_insert_rowid()",null);
 cursor.moveToNext();
 String extra_data = cursor.getString(0);
 cursor.close();
 for(QuestionExtra extra:question.getExtra()) {
 sql = "insert into [Extra_] ([extra_code],[extra_text],[extra_data]) values (?,?,?)";
 database.execSQL(sql, new String[]{""+extra.getExtra_code(),extra.getExtra_text(),extra_data});
 }
 }

//數量增加
 count++;
 sql = "update [Subject_] set [subject_count] = "+count+" where [subject_code] = '"+question.getCode()+"'";
 database.execSQL(sql);
 }

/**
 * 獲取Data_部分
 * @return 題目信息
 */
 public static Cursor GetInfo(String keys, int type_code, String subject_code){
 String sql = "select [data_subject],[data_code],[data_question],[data_keys],[type_name] from [Type_],[Data_] where [type_code] = [data_type] and [data_question] like '%"+keys+"%'";
 if(type_code != 0){
 sql +=" and [data_type] = " + type_code +" and [type_code] = " + type_code;
 }

if(subject_code != null){
 sql +=" and [data_subject] = '"+subject_code+"'";
 }

return database.rawQuery(sql,null);
 }

/**
 * 獲取Extra部分
 * @param code 編號
 * @return 選項信息
 */
 public static Cursor GetExtra(int code){
 String sql = "select [extra_code],[extra_text] from [Extra_] where [extra_data] = " + code;
 return database.rawQuery(sql,null);
 }

/**
 * 獲取題型 或 科目
 * @param table 獲取目標
 * @return Cursor
 */
 public static Cursor GetTypeOrSubject(String table){
 if(table.equals("Type_"))
 return database.rawQuery("select [type_code],[type_name] from [Type_]",null);
 else
 return database.rawQuery("select [subject_code],[subject_name],[subject_count] from [Subject_]",null);
 }

/**
 * 查看錯誤題目
 * @param keys 關鍵字
 * @param type_code 題型
 * @param subject_code 科目
 * @return Cursor
 */
 public static Cursor GetWrong(String keys,int type_code,String subject_code){
 String sql = "select [data_subject],[data_code],[data_question],[data_keys],[type_name] from [Type_],[Data_],[Wrong_] " +
 "where [type_code] = [data_type] and [data_code] = [wrong_data] and [data_question] like '%"+keys+"%'";
 if(type_code != 0){
 sql +=" and [data_type] = " + type_code +" and [type_code] = " + type_code;
 }

if(subject_code != null){
 sql +=" and [data_subject] = '"+subject_code+"'";
 }

return database.rawQuery(sql,null);
 }

/**
 * 刪除指定題目
 * @param question 題目信息
 */
 public static void DeleteQuestion(Question question) {
 //刪除題目
 String sql = "delete from [Data_] where [data_code] = " + question.getNum();
 database.execSQL(sql);

//數量減少
 sql = "select [subject_count] from [Subject_] where [subject_code] = '"+question.getCode()+"'";
 Cursor cursor = database.rawQuery(sql,null);
 cursor.moveToNext();
 int count = cursor.getInt(0);
 cursor.close();
 count--;
 sql = "update [Subject_] set [subject_count] = "+count+" where [subject_code] = '"+question.getCode()+"'";
 database.execSQL(sql);
 }

public static void DeleteSubject(String code){
 //刪除科目
 String sql = "delete from [Subject_] where [subject_code] = '" + code + "'";
 database.execSQL(sql);
 }

/**
 * 添加科目
 * @param code 科目代碼
 * @param name 科目名稱
 */
 public static void AddNewSubject(String code, String name) {
 String sql = "insert into [Subject_] ([subject_code],[subject_name]) values ('"+code+"','"+name+"')" ;
 database.execSQL(sql);
 }
}

考慮到要經常使用所有選擇用static來標識，不過具體情況還是要具體分析。

SQLite裏，一次只能執行一條語句，如果要執行第二條，需要第二次調用相關函數，而不能想管理程序一樣直接用‘;’來輸入多行sql語句。

其他語言也儘量選擇一次執行一條，這樣也方便異常處理。