Question

我需要读取（查询）数据库列的确切行。这是我的提供者的相关数据：

public class TravelOrderProvider extends ContentProvider {

    public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/travelorder");
    private static final int URI_TRAVELORDER = 1;
    private static final int URI_TRAVELORDER_ITEM = 2;
    private static final UriMatcher mUriMatcher;
    static {
        mUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        mUriMatcher.addURI(AUTHORITY, "travelorder", URI_TRAVELORDER);
        mUriMatcher.addURI(AUTHORITY, "travelorder/#", URI_TRAVELORDER_ITEM);
    }

    public class TravelOrder implements BaseColumns {
        public static final String NAME = "name";
        public static final String GROUP = "group";
        public static final String ORDER = "order";
    }

    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        database = mDbHelper.getWritableDatabase();
        int match = mUriMatcher.match(uri);
        SQLiteQueryBuilder qBuilder = new SQLiteQueryBuilder();
        qBuilder.setTables(TravelOrderDatabaseHelper.TABLE_NAME);

        switch (match){
            case URI_TRAVELORDER:
                //nothing
                break;
            case URI_TRAVELORDER_ITEM:
                String id = uri.getPathSegments().get(1);
                qBuilder.appendWhere(TravelOrder._ID + "=" + id);
                break;
            default:
                throw new IllegalArgumentException("Unknown URI: " + uri);
        }
        Cursor c = qBuilder.query(database, projection, selection, selectionArgs, null, null, sortOrder);
        c.setNotificationUri(getContext().getContentResolver(), uri);

        return c;
    }

现在，这就是我在我的活动中尝试做的事情：

private static final String[] PROJECTION = {TravelOrder._ID, TravelOrder.NAME, TravelOrder.GROUP, TravelOrder.ORDER};

Cursor c = getContentResolver().query(TravelOrderProvider.CONTENT_URI, PROJECTION, null, null, null);

我的问题是：如何获得GROUP列的特定行？我现在应该在上面的最后一个代码行中完成，但是我尝试在selection和selectionArgs定义中定义列和行而没有结果。

Answer 1

关于这个问题：

如何获得GROUP列的特定行？

关于如何在Android培训页面上"Read Information from a Database"，有一个很好的解释示例。

引用：

SQLiteDatabase db = mDbHelper.getReadableDatabase();

// Define a projection that specifies which columns from the database
// you will actually use after this query.
String[] projection = {
    FeedEntry._ID,
    FeedEntry.COLUMN_NAME_TITLE,
    FeedEntry.COLUMN_NAME_UPDATED,
    ...
    };

// How you want the results sorted in the resulting Cursor
String sortOrder =
    FeedEntry.COLUMN_NAME_UPDATED + " DESC";

Cursor c = db.query(
    FeedEntry.TABLE_NAME,  // The table to query
    projection,                               // The columns to return
    selection,                                // The columns for the WHERE clause
    selectionArgs,                            // The values for the WHERE clause
    null,                                     // don't group the rows
    null,                                     // don't filter by row groups
    sortOrder                                 // The sort order
    );

因此，通过相应地更改selection和selectionArgs参数，您肯定可以获取数据库的GROUP列的特定行。

例如，假设您要获取与GROUP列的特定值匹配的行。所以你应该像这样设置你的查询：

SQLiteDatabase db = mDbHelper.getReadableDatabase();

/* The columns used for the SELECT statement. */
String[] projection = {
    "ID",
    "GROUP"
};

/* 
* The columns used for the WHERE statement, 
* they should be formatted as a prepared statement.
*/
String selection = "`ID` = ? AND `GROUP` = ?";

/* 
* The arguments that will be replaced for each ? 
* in the above statement. 
*/
String[] selectionArgs = {
    desiredId, desiredGroup
};

String sortOrder = "`ID` ASC";

Cursor c = db.query(
    "MY_TABLE",             // The table to query
    projection,             // The columns to return
    selection,              // The columns for the WHERE clause
    selectionArgs,          // The values for the WHERE clause
    null,                   // don't group the rows
    null,                   // don't filter by row groups
    sortOrder               // The sort order
);

数据库从所选列中获取一行

1 个答案: