Android数据库SqLite实现增删改查

数据库操作的一般流程有以下步骤：
1.首先，写一个数据库操作帮助类Helper，这个类继承自SQLiteOpenHelper.
2.在自己的DAO层借助自己的Helper写数据库操作的一些方法
3.Activity调用DAO层的数据库操作方法进行操作

下面通过一个存储搜索记录的简单例子来了解Android中数据库操作。
一、写一个自己的数据库操作帮助类DbHelper，这个类继承自SQLiteOpenHelper,代码如下：

/**
 * Created by zhpan on 2016/10/27.
 */

public class DbHelper extends SQLiteOpenHelper {

    public static final String TB_NAME= "mydb.db";

    private static final int VERSION = 1;

    public DbHelper(Context context){
        this(context,TB_NAME);
    }

    public DbHelper(Context context, String name) {
        this(context, name, VERSION);
    }

    public DbHelper(Context context, String name, int version) {
        this(context, name, null, version);
    }

    public DbHelper(Context context, String name, SQLiteDatabase.CursorFactory factory,
            int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table if not exists history(id integer primary key autoincrement,item varchar(60))");

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        if(newVersion>oldVersion){
            //  更新数据库
        }
    }
}

二、在DAO层借助DbHelperf封装数据库操作的方法
在封装方法前先定义History的实体类，如下：

/**
 * Created by zhpan on 2016/10/27.
 */

public class SearchHistoryBean {
    private int id;
    private String item;    //搜索条目内容

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getItem() {
        return item;
    }

    public void setItem(String item) {
        this.item = item;
    }
}

接下来在Dao层封装数据库操作（增删改查）的方法，如下：

/**
 * Created by zhpan on 2016/10/27.
 */

public class SearchHistoryDao {


    DbHelper helper;

    public SearchHistoryDao(Context context) {
        helper = new DbHelper(context);
    }

    //添加历史记录
    public boolean insertHistory(SearchHistoryBean history) {
        SQLiteDatabase db = helper.getReadableDatabase();
        try {
            ContentValues values = new ContentValues();
            values.put("item", history.getItem());

            db.insert("history", null, values);

            return true;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            db.close();
        }
        return false;
    }

    //更新历史记录
    public boolean updateHistory(SearchHistoryBean history) {
        SQLiteDatabase db = helper.getReadableDatabase();
        try {
            ContentValues values = new ContentValues();
            values.put("item", history.getItem());
            db.update("history", values, "item = ?", new String[]{history.getId() + ""});
            return true;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            db.close();
        }
        return false;
    }

    //  通过ID删除历史
    public boolean delHistoryById(int id) {
        SQLiteDatabase db = helper.getReadableDatabase();
        try {
            db.delete("history", "id=?", new String[]{id + ""});
            return true;
        } catch (Exception e) {
            e.printStackTrace();//打印错误堆栈信息
        } finally {
            db.close();
        }
        return false;
    }

    //  通过item删除历史
    public boolean delHistoryByItem(String item) {
        SQLiteDatabase db = helper.getReadableDatabase();
        try {
            db.delete("history", "item=?", new String[]{item});

            return true;
        } catch (Exception e) {
            //打印错误堆栈信息
            e.printStackTrace();
        } finally {
            db.close();
        }
        return false;
    }

    //根据id查询历史记录
    public SearchHistoryBean findById(int id) {
        SQLiteDatabase db = helper.getReadableDatabase();
        Cursor cursor = db.query("history", null, "id=?", new String[]{id + ""}, null, null, null);
        SearchHistoryBean history = null;
        if (cursor.moveToNext()) {
            history = new SearchHistoryBean();
            history.setId(id);
            history.setItem(cursor.getString(cursor.getColumnIndex("item")));

        }
        return history;
    }

    //  查询是否已经存在该item
    public boolean isItemExists(String item) {
        SQLiteDatabase db = helper.getReadableDatabase();
        Cursor cursor = db.query("history", null, "item=?", new String[]{item}, null, null, null);
        int count = cursor.getCount();
        cursor.close();
        if (count > 0) {
            return true;
        } else {
            return false;

        }
    }

    //查询所有历史记录
    public List<SearchHistoryBean> findAll() {
        SQLiteDatabase db = helper.getReadableDatabase();
        Cursor cursor = db.query("history", null, null, null, null, null, "id desc");
        List<SearchHistoryBean> list = new ArrayList<>();
        SearchHistoryBean history = null;
        while (cursor.moveToNext()) {
            history = new SearchHistoryBean();
            history.setId(cursor.getInt(cursor.getColumnIndex("id")));
            history.setItem(cursor.getString(cursor.getColumnIndex("item")));
            list.add(history);
        }
        cursor.close();
        return list;
    }

    //查询前limit条历史记录
    public List<SearchHistoryBean> findLimit(int limit) {
        SQLiteDatabase db = helper.getReadableDatabase();
        //Cursor cursor = db.query("history", null, null, null, null, null, "id desc","limit 8");
        Cursor cursor = db.rawQuery("select * from history order by id desc limit ?", new String[]{limit+""});
        List<SearchHistoryBean> list = new ArrayList<>();
        SearchHistoryBean history;
        while (cursor.moveToNext()) {
            history = new SearchHistoryBean();
            history.setId(cursor.getInt(cursor.getColumnIndex("id")));
            history.setItem(cursor.getString(cursor.getColumnIndex("item")));
            list.add(history);
        }
        cursor.close();
        return list;
    }

    //  删除所有历史记录
    public boolean delAll() {
        SQLiteDatabase db = helper.getReadableDatabase();
        db.execSQL("delete from history");
        return false;
    }

}

完成以上操作后即可在Activity中通过SearchHistoryDao调用封装好的方法实现数据库增删改查的操作。