如何使用 GreenDao ORM 库从 Android 中的资产创建数据库 [英] How to create database from Assets in Android using GreenDao ORM library

问题描述

我正在使用 GreenDao orm 库来创建数据库，它适用于从代码中创建数据库的第一个示例.

I am using GreenDao orm library for creating database, it works good with the First sample for Creating Database, from within the code.

现在的问题是我找不到任何文档或任何与数据库从资产文件夹复制到内存中的数据库相关的内容.

Now the problem is I can't find any documentation or anything related to the Database copying from Assets Folder to the databases inside memory.

推荐答案

接受的答案提供了一个解决方案，但它只是部分正确.查看我在下面发布的课程.这是greenDao 的OpenHelper 类的扩展.下面是它的使用示例以及如何使用它代替 OpenHelper 或 DevOpenHelper 来管理 sqlite 数据库的副本.

The accepted answer provides a solution but it's only partially correct. Check out the class I posted below. This is an extension of greenDao's OpenHelper class. Below that is an example of it's use and how you can use it instead of OpenHelper or DevOpenHelper to manage the copy of your sqlite database.

package com.example;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import com.example.R;
import com.example.DaoMaster.OpenHelper;

public class DatabaseOpenHelper extends OpenHelper {

    private Context context;

    private SQLiteDatabase sqliteDatabase;

    private static String DB_PATH;

    private static String DB_NAME;

    public DatabaseOpenHelper(Context context, String name, CursorFactory factory) {
        super(context, name, factory);
        this.context = context;
        this.DB_NAME = name;
        this.DB_PATH = context.getString(R.string.DB_PATH);
        try {
            createDataBase();
        } catch (Exception ioe) {
            throw new Error("Unable to create database");
        }
    }

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

    }

    /** Open Database for Use */
    public void openDatabase() {
        String databasePath = DB_PATH + DB_NAME;
        sqliteDatabase = SQLiteDatabase.openDatabase(databasePath, null,
                (SQLiteDatabase.OPEN_READWRITE));
    }

    /** Close Database after use */
    @Override
    public synchronized void close() {
        if ((sqliteDatabase != null) && sqliteDatabase.isOpen()) {
            sqliteDatabase.close();
        }
        super.close();
    }

    /** Get database instance for use */
    public SQLiteDatabase getSqliteDatabase() {
        return sqliteDatabase;
    }

    /** Create new database if not present */
    public void createDataBase() {
        SQLiteDatabase sqliteDatabase = null;

        if (databaseExists()) {
            /* Check for Upgrade */
        } else {
            /* Database does not exists create blank database */
            sqliteDatabase = this.getReadableDatabase();
            sqliteDatabase.close();

            copyDataBase();
        }
    }

    /** Check Database if it exists */
    private boolean databaseExists() {
        SQLiteDatabase sqliteDatabase = null;
        try {
            String databasePath = DB_PATH + DB_NAME;
            sqliteDatabase = SQLiteDatabase.openDatabase(databasePath, null,
                    SQLiteDatabase.OPEN_READONLY);
        } catch (SQLiteException e) {
            e.printStackTrace();
        }

        if (sqliteDatabase != null) {
            sqliteDatabase.close();
        }
        return sqliteDatabase != null ? true : false;
    }

    /**
     * Copy existing database file in system
     */
    public void copyDataBase() {

        int length;
        byte[] buffer = new byte[1024];
        String databasePath = DB_PATH + DB_NAME;

        try {
            InputStream databaseInputFile = this.context.getAssets().open(DB_NAME+".sqlite");
            OutputStream databaseOutputFile = new FileOutputStream(databasePath);

            while ((length = databaseInputFile.read(buffer)) > 0) {
                databaseOutputFile.write(buffer, 0, length);
                databaseOutputFile.flush();
            }
            databaseInputFile.close();
            databaseOutputFile.close();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

所以这是它的用法示例:

So here is an example of it's usage:

DatabaseOpenHelper helper = new DatabaseOpenHelper(this, "db", null);
db = helper.getWritableDatabase();
daoMaster = new DaoMaster(db);
daoSession = daoMaster.newSession();

这篇关于如何使用 GreenDao ORM 库从 Android 中的资产创建数据库的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！