目前推荐使用哪种SQLite设计模式？

Question

我正在考虑为我的应用程序的数据库实现单例设计模式，而不是经历制作和销毁数据库实例的代价高昂的操作。

然而，稍后我会读到，有几个Android和SQLite的选项（但我不记得是什么，我找不到链接），所以我想知道，这些数据库推荐哪些设计模式，以及它们的优点/缺点是什么？

感谢， 利亚姆

Answer 1

我用这种形式给出。我使用这些单例类SQLiteHelper，SelectionBuilder。

public class SQLiteHelper extends SQLiteOpenHelper { 

public static final int DATABASE_VERSION = 1; 
public static final String DATABASE_NAME = "test.db"; 

public static final String PRIMARY_KEY = " PRIMARY KEY"; 
public static final String TYPE_TEXT = " TEXT"; 
public static final String TYPE_INTEGER = " INTEGER"; 
public static final String TYPE_REAL = " REAL"; 
public static final String COMMA_SEP = ","; 

public SQLiteHelper(Context context) { 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    db.execSQL(Category.SQL_CREATE_TABLE); 
    db.execSQL(Article.SQL_CREATE_TABLE); 
    db.execSQL(IntroImage.SQL_CREATE_TABLE); 
    db.execSQL(Asset.SQL_CREATE_TABLE); 
} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    db.execSQL(Category.SQL_DROP_TABLE); 
    db.execSQL(Article.SQL_DROP_TABLE); 
    db.execSQL(IntroImage.SQL_DROP_TABLE); 
    db.execSQL(Asset.SQL_DROP_TABLE); 
} 

}

SQLiteOpenHelper是的DB创建和升级单。 SelectionBuilder的名字就是帮助构建选择条款。

public class SelectionBuilder { 
private static final String TAG = SelectionBuilder.class.getSimpleName(); 

private String mTable = null; 
private Map<String, String> mProjectionMap = Maps.newHashMap(); 
private StringBuilder mSelection = new StringBuilder(); 
private ArrayList<String> mSelectionArgs = Lists.newArrayList(); 

/** 
* Reset any internal state, allowing this builder to be recycled. 
*/ 
public SelectionBuilder reset() { 
    mTable = null; 
    mSelection.setLength(0); 
    mSelectionArgs.clear(); 
    return this; 
} 

/** 
* Append the given selection clause to the internal state. Each clause is 
* surrounded with parenthesis and combined using {@code AND}. 
*/ 
public SelectionBuilder where(String selection, String... selectionArgs) { 
    if (TextUtils.isEmpty(selection)) { 
     if (selectionArgs != null && selectionArgs.length > 0) { 
      throw new IllegalArgumentException(
        "Valid selection required when including arguments="); 
     } 

     // Shortcut when clause is empty 
     return this; 
    } 

    if (mSelection.length() > 0) { 
     mSelection.append(" AND "); 
    } 

    mSelection.append("(").append(selection).append(")"); 
    if (selectionArgs != null) { 
     Collections.addAll(mSelectionArgs, selectionArgs); 
    } 

    return this; 
} 

public SelectionBuilder table(String table) { 
    mTable = table; 
    return this; 
} 

private void assertTable() { 
    if (mTable == null) { 
     throw new IllegalStateException("Table not specified"); 
    } 
} 

public SelectionBuilder mapToTable(String column, String table) { 
    mProjectionMap.put(column, table + "." + column); 
    return this; 
} 

public SelectionBuilder map(String fromColumn, String toClause) { 
    mProjectionMap.put(fromColumn, toClause + " AS " + fromColumn); 
    return this; 
} 

/** 
* Return selection string for current internal state. 
* 
* @see #getSelectionArgs() 
*/ 
public String getSelection() { 
    return mSelection.toString(); 
} 

/** 
* Return selection arguments for current internal state. 
* 
* @see #getSelection() 
*/ 
public String[] getSelectionArgs() { 
    return mSelectionArgs.toArray(new String[mSelectionArgs.size()]); 
} 

private void mapColumns(String[] columns) { 
    for (int i = 0; i < columns.length; i++) { 
     final String target = mProjectionMap.get(columns[i]); 
     if (target != null) { 
      columns[i] = target; 
     } 
    } 
} 

@Override 
public String toString() { 
    return "SelectionBuilder[table=" + mTable + ", selection=" + getSelection() 
      + ", selectionArgs=" + Arrays.toString(getSelectionArgs()) + "]"; 
} 

/** 
* Execute query using the current internal state as {@code WHERE} clause. 
*/ 
public Cursor query(SQLiteDatabase db, String[] columns, String orderBy) { 
    return query(db, columns, null, null, orderBy, null); 
} 

/** 
* Execute query using the current internal state as {@code WHERE} clause. 
*/ 
public Cursor query(SQLiteDatabase db, String[] columns, String groupBy, 
        String having, String orderBy, String limit) { 
    assertTable(); 
    if (columns != null) mapColumns(columns); 
    Log.v(TAG, "query(columns=" + Arrays.toString(columns) + ") " + this); 
    return db.query(mTable, columns, getSelection(), getSelectionArgs(), groupBy, having, 
      orderBy, limit); 
} 

/** 
* Execute distinct query using the current internal state as {@code WHERE} clause. 
*/ 
public Cursor queryDistinct(SQLiteDatabase db, String[] columns, String orderBy) { 
    return queryDistinct(db, columns, null, null, orderBy, null); 
} 
/** 
* Execute distinct query using the current internal state as {@code WHERE} clause. 
*/ 
public Cursor queryDistinct(SQLiteDatabase db, String[] columns, String groupBy, 
        String having, String orderBy, String limit) { 
    assertTable(); 
    if (columns != null) mapColumns(columns); 
    Log.v(TAG, "queryDistinct(columns=" + Arrays.toString(columns) + ") " + this); 
    return db.query(true, mTable, columns, getSelection(), getSelectionArgs(), groupBy, having, 
      orderBy, limit); 
} 

/** 
* Execute update using the current internal state as {@code WHERE} clause. 
*/ 
public int update(SQLiteDatabase db, ContentValues values) { 
    assertTable(); 
    Log.v(TAG, "update() " + this); 
    return db.update(mTable, values, getSelection(), getSelectionArgs()); 
} 

/** 
* Execute delete using the current internal state as {@code WHERE} clause. 
*/ 
public int delete(SQLiteDatabase db) { 
    assertTable(); 
    Log.v(TAG, "delete() " + this); 
    return db.delete(mTable, getSelection(), getSelectionArgs()); 
} 
} 

所以这两个帮手，你可以用的ContentProvider结合为您创建和使用这些帮助你定义你的查询，插入，更新和删除方法的模型。另外对我来说，最好的办法是将Google Sync Framework与Loaders结合使用。

http://developer.android.com/training/sync-adapters/index.html