我如何在我的项目中使用预先创建的数据库

Question

package com.m;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class HellowWebView extends SQLiteOpenHelper {
    static final String UR_DB_NAME="mimo.sqlite";
    public static final String KEY_ROWID = "_syid"; 
    public static final String KEY_ROWIDc = "_conid";
    static final String tableName = "CATEGORY";
    static final String New_tableName = "CATEGORY_NEW";
    static final String col_name = "NAME";
    static final String col_id = "PARENT_ID";
    static final String col_name_new = "NAME";
    static final String col_id_new = "PARENT_ID";
    public static final int version='1';
    public static Context context;

    SQLiteDatabase sql;

    public HellowWebView(Context context) {
        super(context, UR_DB_NAME, null, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        try{
        sql = context.openOrCreateDatabase(UR_DB_NAME, 0, null);
        getWritableDatabase();
        db.execSQL("CREATE TABLE " + New_tableName + "(_syid INTEGER PRIMARY 
KEY,col_name_new TEXT,col_id_new NUMBER)");     
        db.execSQL("INSERT INTO UR_DB_NAME.New_tableName(col_name_new,col_id_new) 
SELECT * from tableName",null);
        db.close();
        }catch(Exception e){
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
    }
}

Answer 1

您可以在创建的db文件中复制现有的db文件：为此，您可以按照以下步骤进行操作 -

1. 检查现有数据库。 （第一次没有数据库）。
2. 创建数据库。
3. 现在，您将在创建的db文件上以实用方式替换预先创建的数据库。

以下是可供参考的代码：

 private boolean checkDataBase() {
    try {
        String myPath = DB_PATH + DB_NAME;
        try {
            Log.v("---DatabaseHelper--",
                    "---within checkDataBase opening database----");
            myDataBase = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY);

        } catch (SQLiteException e) {
            Log.v("---DatabaseHelper--", "---within checkDataBase----" + e);

        }

        if (myDataBase != null) {

            myDataBase.close();

        }
    } catch (Throwable e) {
        StringWriter errorLog = new StringWriter();
        e.printStackTrace(new PrintWriter(errorLog));
        serverComm.sendErrorLog(errorLog.toString());

    }

    return myDataBase != null ? true : false;
}

然后getReadableDatabase（），为你的应用程序创建一个空白数据库..然后用你的数据库替换它你将它放在资产文件夹中 -

private void copyDataBase() throws IOException {
    try {
        Log.v("---DatabaseHelper--", "---within copyDataBase----");

        // Open your local db as the input stream
        InputStream myInput = myContext.getAssets().open(
                "DB_NAME.sqlite");
        // Path to the just created empty db
        String outFileName = DB_PATH + DB_NAME;
        // Open the empty db as the output stream
        OutputStream myOutput = new FileOutputStream(outFileName);
        // transfer bytes from the inputfile to the outputfile
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myInput.read(buffer)) > 0) {
            myOutput.write(buffer, 0, length);

        }
        Log.v("---DatabaseHelper--", "--- after coping----");
        // Close the streams
        myOutput.flush();
        myOutput.close();
        myInput.close();
    } catch (Throwable e) {
        StringWriter errorLog = new StringWriter();
        e.printStackTrace(new PrintWriter(errorLog));
        serverComm.sendErrorLog(errorLog.toString());

    }

}

Answer 2

这个here有一个很好的解决方案。

1. 准备SQLite数据库文件。

假设您已经创建了sqlite数据库，我们需要对其进行一些修改。 如果您没有sqlite管理器，我建议您下载适用于Win / Linux / Mac的开源SQLite数据库浏览器。

打开数据库并添加一个名为“android_metadata”的新表，您可以执行以下SQL语句来执行此操作：

CREATE TABLE "android_metadata" ("locale" TEXT DEFAULT 'en_US')

现在在“android_metadata”表中插入一行文本“en_US”：

INSERT INTO "android_metadata" VALUES ('en_US')

然后，有必要将表的主id字段重命名为“_id”，以便Android知道绑定表的id字段的位置。 您可以使用SQLite数据库浏览器轻松执行此操作，方法是按编辑表按钮编辑表，然后选择要编辑的表，最后选择要重命名的字段。

将所有数据表的id字段重命名为“_id”并添加“android_metadata”表后，您的数据库就可以在Android应用程序中使用了。



注意：在此图片中，我们会看到表格“类别”和“内容”，其中ID字段已重命名为“_id”，而刚刚添加的表格为“android_metadata”。

1. 在Android中复制，打开和访问您的数据库 应用

现在只需将数据库文件放在项目的“assets”文件夹中，并通过从“android.database.sqlite”包中扩展SQLiteOpenHelper类来创建Database Helper类。

使您的DataBaseHelper类看起来像这样：

public class DataBaseHelper extends SQLiteOpenHelper{

//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/YOUR_PACKAGE/databases/";

private static String DB_NAME = "myDBName";

private SQLiteDatabase myDataBase;

private final Context myContext;

/**
  * Constructor
  * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
  * @param context
  */
public DataBaseHelper(Context context) {

super(context, DB_NAME, null, 1);
this.myContext = context;
}   

/**
  * Creates a empty database on the system and rewrites it with your own database.
  * */
public void createDataBase() throws IOException{

boolean dbExist = checkDataBase();

if(dbExist){
//do nothing - database already exist
}else{

//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();

try {

copyDataBase();

} catch (IOException e) {

throw new Error("Error copying database");

}
}

}

/**
  * Check if the database already exist to avoid re-copying the file each time you open the application.
  * @return true if it exists, false if it doesn't
  */
private boolean checkDataBase(){

SQLiteDatabase checkDB = null;

try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

}catch(SQLiteException e){

//database does't exist yet.

}

if(checkDB != null){

checkDB.close();

}

return checkDB != null ? true : false;
}

/**
  * Copies your database from your local assets-folder to the just created empty database in the
  * system folder, from where it can be accessed and handled.
  * This is done by transfering bytestream.
  * */
private void copyDataBase() throws IOException{

//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);

// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;

//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);

//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}

//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();

}

public void openDataBase() throws SQLException{

//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

}

@Override
public synchronized void close() {

if(myDataBase != null)
myDataBase.close();

super.close();

}

@Override
public void onCreate(SQLiteDatabase db) {

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

// Add your public helper methods to access and get content from the database.
// You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
// to you to create adapters for your views.

}

就是这样。 现在，您可以创建此DataBaseHelper类的新实例，并调用createDataBase（）和openDataBase（）方法。请记住将“YOUR_PACKAGE”更改为DB_PATH字符串中的应用程序包命名空间（即：com.examplename.myapp）。

 ...

    DataBaseHelper myDbHelper = new DataBaseHelper();
    myDbHelper = new DataBaseHelper(this);

    try {

    myDbHelper.createDataBase();

    } catch (IOException ioe) {

    throw new Error("Unable to create database");

    }

    try {

    myDbHelper.openDataBase();

    }catch(SQLException sqle){

    throw sqle;

    }

    ...