這篇文章是資料庫系列篇文章的第一篇，主要講Android Sqlite資料庫儲存，後面陸續出GreenDao，LitePal, Realm,wcdb的文章，一如既往，如果遇到任何關於Android中SQLite的問題，都可以直接在我的文章底部留言，或者直接在我的公眾號aserbao留言，文章會持續更新，希望這篇文章能為大家提供到幫助！如果覺得文章對你有用，就幫忙點個贊，若覺得文章寫得不好之處望指出，必將加以修正！

這篇文章主要講SQlite資料庫儲存，從資料庫建表到資料庫的增刪改查操作，再到資料庫升級操作，最後是文章總結及參考連結

專案效果地址：

SQlite

1. 建立資料庫

Android中使用SQlite，需要自己建立庫，建表，新增資料！好在Android中提供了SQLiteOpenHelper類來幫助建立使用資料庫，我們只需要繼承這個類就可以實現資料庫的建立和對資料的操作了！Android 中建立資料庫需要通過如下幾部：

1. 建立一個類繼承SQLiteOpenHelper，需要實現其三個方法：
   • 構造方法：需要給SQLiteOpenHelper傳遞四個引數:(上下文，資料庫名，遊標工廠(通常為null)，當前資料庫版本號)；
   • onCreate(): 表的建立，初始化操作
   • onUpgrade(): 表升級
   • 還有：onDowngrade(): 表降級,onOpen：每次開啟資料庫，onBeforeDelete：

public class ThingManagerDBOpenHelper extends SQLiteOpenHelper {
    public static final String DB_NAME = "mysql.db";
    private static final int VERSION = 1;
    public ThingManagerDBOpenHelper(Context context) {
        super(context, DB_NAME, null, VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE IF NOT EXISTS "
                + ThingDBController.TABLE_NAME
                + String.format(
                "("
                        + "%s INTEGER PRIMARY KEY AUTOINCREMENT, "
                        + "%s VARCHAR, "
                        + "%s INTEGER"
                        +")"
                , ThingManagerDBModel.ID
                , ThingManagerDBModel.MESSAGE
                , ThingManagerDBModel.TIME
        )) ;
    }


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

說下SQlite的資料型別 ：

2. 建立一個數據庫儲存物件

public final class ThingManagerDBModel {
    public static final String TABLE_NAME = "mysql_thing";
    public static final String ID = "_id";
    public static final String MESSAGE = "message";
    public static final String TIME = "time";

    int id;
    String message;
    long time;

    public int getId() {
        return id;
    }

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

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public long getTime() {
        return time;
    }

    public void setTime(long time) {
        this.time = time;
    }

    public ContentValues toContentValues(){
        ContentValues cv = new ContentValues();
        cv.put(MESSAGE, message);
        cv.put(TIME, time);
        return cv;
    }
}

3. 建立一個數據庫控制器實現增刪改查

1. 增

1. 使用Android APi來實現增加資料

 public boolean insertApi(int id, String message, long time){
        ThingManagerDBModel dbModel = new ThingManagerDBModel();
        if(id >= 0) {
            dbModel.id = id;
        }
        dbModel.message = message;
        dbModel.time = time;
        final boolean success = db.insert(TABLE_NAME, null, dbModel.toContentValues()) != -1;
        dbClose();
        return success;
    }

2. 使用Sql語句實現增加資料

 public void insertRaw(String message, long time){
        String sql = " insert into " + TABLE_NAME + "(message,time) values(?,?)";
        Object[] args = {message,time};
        db.execSQL(sql,args);
        dbClose();
    }

2. 刪

1. 使用Api

  public boolean deleteApi(String whereClause,String[] whereArgs){
        boolean sucess = db.delete(TABLE_NAME, whereClause,whereArgs) != -1;
        dbClose();
        return sucess;
    }

3. 使用Sql語句

 public void deleteRaw(String message){
        String sql = "delete from "+TABLE_NAME + " where message = ?";
        Object[] args = {message};
        db.execSQL(sql,args);
        dbClose();
    }

3. 改

1. 使用api

public boolean updateApi(int id,String message,long time){
        ThingManagerDBModel dbModel = new ThingManagerDBModel();
        if(id >= 0) {
            dbModel.id = id;
        }
        dbModel.message = message;
        dbModel.time = time;
        boolean success = db.update(TABLE_NAME, dbModel.toContentValues(), "_id = ?", new String[]{String.valueOf(id)}) != -1;
        dbClose();
        return success;
    }

2. 使用Sql條件修改

public void updateRaw(int id,String message,long time){
        String sql = "update "+TABLE_NAME + " set message = ?,time = ? where _id = ?";
        Object[] args = {message,time,id};
        db.execSQL(sql,args);
        dbClose();
    }

4. 查

1. 使用Api

/**
     * @param cloums 要查詢的欄位
     * @param selection 查詢條件
     * @param selectionArgs 填充查詢條件的值
     * @return
     */
    public List<Thing> queryApi(String[] cloums,String selection,String[]  selectionArgs){
        try {
            Cursor c = db.query(TABLE_NAME, cloums, selection, selectionArgs, null, null, null);
            ArrayList<Thing> arrayList = new ArrayList<>();
            if (!c.moveToLast()) {
                return arrayList;
            }
            do {
                Thing model = new Thing();
                model.setId(c.getInt(c.getColumnIndexOrThrow(ThingManagerDBModel.ID)));
                model.setTime(c.getLong(c.getColumnIndexOrThrow(ThingManagerDBModel.TIME)));
                model.setMessage(c.getString(c.getColumnIndexOrThrow(ThingManagerDBModel.MESSAGE)));
                arrayList.add(model);
            } while (c.moveToPrevious());
            c.close();
            return arrayList;
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            dbClose();
        }

        return new ArrayList<>();
    }

3. 使用sql條件

 public List<Thing> queryRawById(String  id){
 	//cursor獲取的一定是在這裡申明的查詢條件值
        String sql = "select _id,message,time from "+TABLE_NAME + " where _id = ?";
        Cursor cursor = db.rawQuery(sql, new String[]{id});
        ArrayList<Thing> arrayList = new ArrayList<>();
        if (!cursor.moveToLast()) {
            return arrayList;
        }
        do {
            Thing model = new Thing();
            model.setId(cursor.getInt(cursor.getColumnIndex(ThingManagerDBModel.ID)));
            model.setTime(cursor.getLong(cursor.getColumnIndex(ThingManagerDBModel.TIME)));
           model.setMessage(cursor.getString(cursor.getColumnIndexOrThrow(ThingManagerDBModel.MESSAGE)));
            arrayList.add(model);
        } while (cursor.moveToPrevious());
        cursor.close();
        dbClose();
        return arrayList;
    }

4. 資料庫的升級

在開發的過程中，我們避免不了需要修改資料庫結構，新增欄位或者刪除欄位！我們通過增加傳遞給SQLiteOpenHelper的版本值，得到onUpgrade方法的回撥來實現對資料庫的操作來進行升級。這裡需要注意的是，如果使用者安裝版本1之後直接跳裝版本3，這時候我們就需要在onUpgrade方法中通過oldVersion來進行每一個版本的逐漸升級，方法如下：

public class ThingManagerDBOpenHelper extends SQLiteOpenHelper {
    public static final String DB_NAME = "mysql.db";
    private static final int VERSION = 3;
    ……
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        switch (oldVersion){
            case 1:
                upToDbVersion2(db);
            case 2:
                upToDbVersion3(db);
            default:
              break;
        }
    }
    public void upToDbVersion2(SQLiteDatabase db){
        db.execSQL("ALTER TABLE " + ThingDBController.TABLE_NAME + " ADD COLUMN add_user_name text");
    }

    public void upToDbVersion3(SQLiteDatabase db) {
        ContentValues values = new ContentValues();
        values.put("message", "版本升級後的資料");
        db.update(ThingDBController.TABLE_NAME, values, null, null);
    }
}

問題

查詢問題

Cursor只會擁有你查詢的資料，如果在查詢條件裡面沒有申請，Cursor裡面就不會包含這個值，就會出現如下異常：
錯誤寫法：

 String sql = "select message,time from "+TABLE_NAME + " where _id = ?";//條件裡面沒有申請查詢_id的值
 ……something……
 model.setId(cursor.getInt(cursor.getColumnIndex(ThingManagerDBModel.ID)));//在這裡提取會報異常

正確寫法：

 String sql = "select  _id,message,time from "+TABLE_NAME + " where _id = ?";//條件裡面沒有申請查詢_id的值
 ……something……
 model.setId(cursor.getInt(cursor.getColumnIndex(ThingManagerDBModel.ID)));//這裡進行id值的提取

異常：

  java.lang.IllegalStateException: Couldn't read row 0, col -1 from CursorWindow.  Make sure the Cursor is initialized correctly before accessing data from it.
        at android.database.CursorWindow.nativeGetLong(Native Method)
        at android.database.CursorWindow.getLong(CursorWindow.java:513)
        at android.database.CursorWindow.getInt(CursorWindow.java:580)
        at android.database.AbstractWindowedCursor.getInt(AbstractWindowedCursor.java:69)
        at com.aserbao.aserbaosandroid.functions.database.mySql.beans.ThingDBController.queryRawById(ThingDBController.java:109)
        at com.aserbao.aserbaosandroid.functions.database.mySql.MySqlActivity.queryData(MySqlActivity.java:70)
        at com.aserbao.aserbaosandroid.functions.database.base.DataBaseBaseActivity.onViewClicked(DataBaseBaseActivity.java:85)
        at com.aserbao.aserbaosandroid.functions.database.base.DataBaseBaseActivity_ViewBinding$2.doClick(DataBaseBaseActivity_ViewBinding.java:48)
        at butterknife.internal.DebouncingOnClickListener.onClick(DebouncingOnClickListener.java:22)
        at android.view.View.performClick(View.java:6291)
        at android.view.View$PerformClick.run(View.java:24931)
        at android.os.Handler.handleCallback(Handler.java:808)
        at android.os.Handler.dispatchMessage(Handler.java:101)
        at android.os.Looper.loop(Looper.java:166)
        at android.app.ActivityThread.main(ActivityThread.java:7425)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)

參考連結