Android:ContentResolver中的Distinct和GroupBy

Question

什么是添加一种合适的方式DISTINCT和/或GROUPBY以ContentResolver-基于查询.现在我必须为每个特殊情况创建自定义URI.有没有更好的办法？(我仍以1.5为最低共同标准编程)

Answer 1

在查询contentResolver时你可以做得很好,使用:

String selection = Models.SOMETHING + "=" + something + ") GROUP BY (" + Models.TYPE;

Answer 2

由于没有人来回答我只是想告诉我如何解决这个问题.基本上我会为每个案例创建自定义URI并传递selection参数中的条件.然后在里面ContentProvider#query我将识别案例并根据表名和选择参数构造原始查询.

这是一个简单的例子:

switch (URI_MATCHER.match(uri)) {
    case TYPES:
        table = TYPES_TABLE;
        break;
    case TYPES_DISTINCT:
        return db.rawQuery("SELECT DISTINCT type FROM types", null);
    default:
        throw new IllegalArgumentException("Unknown URI " + uri);
    }
    return db.query(table, null, selection, selectionArgs, null, null, null);

Answer 3

如果要将DISTINCT与SELECT一起使用多一列,则需要使用GROUP BY.
使用以下内容的Mini Hack over ContentResolver.query:

Uri uri = Uri.parse("content://sms/inbox");
        Cursor c = getContentResolver().query(uri, 
            new String[]{"DISTINCT address","body"}, //DISTINCT
            "address IS NOT NULL) GROUP BY (address", //GROUP BY
            null, null);
        if(c.moveToFirst()){
            do{
                Log.v("from", "\""+c.getString(c.getColumnIndex("address"))+"\"");
                Log.v("text", "\""+c.getString(c.getColumnIndex("body"))+"\"");

            } while(c.moveToNext());
        }

此代码从设备收件箱中为每个发件人选择最后一个短信.
注意:在GROUP BY之前,我们总是需要编写至少一个条件.结果ContentResolver.query方法中的SQL查询字符串将:

SELECT DISTINCT address, body FROM sms WHERE (type=1) AND (address IS NOT NULL) GROUP BY (address) 

Answer 4

在重写的ContentProvider查询方法中,有一个特定的URI映射到使用distinct.

然后使用SQLiteQueryBuilder并调用该setDistinct(boolean)方法.

@Override
public Cursor query(Uri uri, String[] projection, String selection,
        String[] selectionArgs, String sortOrder)
{
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();

    boolean useDistinct = false;

    switch (sUriMatcher.match(uri))
    {
    case YOUR_URI_DISTINCT:
        useDistinct = true;
    case YOUR_URI:
        qb.setTables(YOUR_TABLE_NAME);
        qb.setProjectionMap(sYourProjectionMap);
        break;

    default:
        throw new IllegalArgumentException("Unknown URI " + uri);
    }

    // If no sort order is specified use the default
    String orderBy;
    if (TextUtils.isEmpty(sortOrder))
    {
        orderBy = DEFAULT_SORT_ORDER;
    }
    else
    {
        orderBy = sortOrder;
    }
    // Get the database and run the query
    SQLiteDatabase db = mDBHelper.getReadableDatabase();
            // THIS IS THE IMPORTANT PART!
    qb.setDistinct(useDistinct);
    Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, orderBy);

    if (c != null)
    {
        // Tell the cursor what uri to watch, so it knows when its source data changes
        c.setNotificationUri(getContext().getContentResolver(), uri);
    }

    return c;
}

Answer 5

虽然我没有使用Group By,但我在内容解析器查询中使用了Distinct.

Cursor cursor = contentResolver .query(YOUR_URI, new String[] {"Distinct "+ YOUR_COLUMN_NAME}, null, null, null);