Android ContentProvider URI方案，用于通知CursorAdapters监听OUTER JOIN查询

I have an Android ContentProvider which allows to do LEFT OUTER JOIN queries on a SQLite database.

我有一个Android ContentProvider，允许在SQLite数据库上执行LEFT OUTER JOIN查询。

Let's assume in the database I have 3 tables, Users, Articles and Comments. The ContentProvider is something like the following:

让我们假设在数据库中我有3个表，用户，文章和评论。 ContentProvider类似于以下内容：

public class SampleContentProvider extends ContentProvider {
    private static final UriMatcher sUriMatcher;
    public static final String AUTHORITY = "com.sample.contentprovider";
    private static final int USERS_TABLE = 1;
    private static final int USERS_TABLE_ID = 2;
    private static final int ARTICLES_TABLE = 3;
    private static final int ARTICLES_TABLE_ID = 4;
    private static final int COMMENTS_TABLE = 5;
    private static final int COMMENTS_TABLE_ID = 6;
    private static final int ARTICLES_USERS_JOIN_TABLE = 7;
    private static final int COMMENTS_USERS_JOIN_TABLE = 8;

    // [...] other ContentProvider methods

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

        // SQLiteWrapper is a wrapper class to manage a SQLiteHelper
        Cursor c = SQLiteWrapper.get(getContext()).getHelper().getReadableDatabase()
                .query(table, projection, selection, selectionArgs, null, null, sortOrder);

        c.setNotificationUri(getContext().getContentResolver(), uri);
        return c;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        String table = getTableName(uri);

        // SQLiteWrapper is a wrapper class to manage a SQLiteHelper
        long id = SQLiteWrapper.get(getContext()).getHelper().getWritableDatabase()
                .insert(table, null, values);

        Uri itemUri = ContentUris.withAppendedId(uri, id);
        getContext().getContentResolver().notifyChange(itemUri, null);

        return itemUri;
    }

    private String getTableName(Uri uri) {
        switch (sUriMatcher.match(uri)) {
        case USERS_TABLE:
        case USERS_TABLE_ID:
            return "Users";

        case ARTICLES_TABLE:
        case ARTICLES_TABLE_ID:
            return "Articles";

        case COMMENTS_TABLE:
        case COMMENTS_TABLE_ID:
            return "Comments";

        case ARTICLES_USERS_JOIN_TABLE:
            return "Articles a LEFT OUTER JOIN Users u ON (u._id = a.user_id)";

        case COMMENTS_USERS_JOIN_TABLE:
            return "Comments c LEFT OUTER JOIN Users u ON (u._id = c.user_id)";

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

    static {
        sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        sUriMatcher.addURI(AUTHORITY, "users", USERS_TABLE);
        sUriMatcher.addURI(AUTHORITY, "articles", ARTICLES_TABLE);
        sUriMatcher.addURI(AUTHORITY, "comments", COMMENTS_TABLE);
        sUriMatcher.addURI(AUTHORITY, "users" + "/#", USERS_TABLE_ID);
        sUriMatcher.addURI(AUTHORITY, "articles" + "/#", ARTICLES_TABLE_ID);
        sUriMatcher.addURI(AUTHORITY, "comments" + "/#", COMMENTS_TABLE_ID);
        sUriMatcher.addURI(AUTHORITY, "???", ARTICLES_USERS_JOIN_TABLE); // what uri here?
        sUriMatcher.addURI(AUTHORITY, "???", COMMENTS_USERS_JOIN_TABLE); // what uri here?
    }
}

What's the best URI scheme to notify all CursorAdapters listening on joined and non-joined queries every time I insert (or update) a row in the Users table?

每次在Users表中插入（或更新）行时，通知所有监听已加入和未加入查询的CursorAdapter的最佳URI方案是什么？

In other words, if I add or update a new row in one of the tables, I want to send a single notification with getContext().getContentResolver().notifyChange(itemUri, null) so that all the CursorAdapters listening on any query (USERS_TABLE, ARTICLES_USERS_JOIN_TABLE, COMMENTS_USERS_JOIN_TABLE) receive a notification to update their content.

换句话说，如果我在其中一个表中添加或更新新行，我想用getContext（）。getContentResolver（）。notifyChange（itemUri，null）发送一个通知，以便所有CursorAdapters监听任何查询（ USERS_TABLE，ARTICLES_USERS_JOIN_TABLE，COMMENTS_USERS_JOIN_TABLE）会收到更新其内容的通知。

If this is not possible, is there an alternative way to notify all the observers?

如果这是不可能的，是否有另一种方式通知所有观察者？

2 个解决方案

#1

You can have special Uri's to query with:

您可以使用特殊的Uri来查询：

    sUriMatcher.addURI(AUTHORITY, "articlesusers", ARTICLES_USERS_JOIN_TABLE);
    sUriMatcher.addURI(AUTHORITY, "commentsusers", COMMENTS_USERS_JOIN_TABLE);

But I can't think of a way to send a single notification. It seems your best choice is to send a notification for each Uri that refers to the table being modified. So your insert/update/delete methods would call notifyChange multiple times depending on the table affected. For changes to "users" it would be 3 notifications--users, articlesusers and commentsusers--since they all depend on the "users" table.

但我想不出发送单一通知的方法。看来你最好的选择是为每个引用被修改表的Uri发送通知。因此，您的插入/更新/删除方法会多次调用notifyChange，具体取决于受影响的表。对于“用户”的更改，它将是3个通知 - 用户，文章用户和评论用户 - 因为它们都依赖于“用户”表。

#2

As answered by prodaea, here is another alternative you can use for notification Uri. This is not a perfect solution, but it uses only one Uri for notification.

正如prodaea所回答的，这是另一种可以用于通知Uri的替代方案。这不是一个完美的解决方案，但它只使用一个Uri进行通知。

The solution is to use the main Uri without any table name (e.g:content://com.example.app.provider/) as the notification Uri in the query method for ARTICLES_USERS_JOIN_TABLE and COMMENTS_USERS_JOIN_TABLE. So, the related cursor will be notified whenever there is change in any table. There is one limitation though. That is, ARTICLES_USERS_JOIN_TABLE cursor will be notified even when there is change in Articles table.

解决方案是使用主要的Uri而不使用任何表名（例如：content：//com.example.app.provider/）作为ARTICLES_USERS_JOIN_TABLE和COMMENTS_USERS_JOIN_TABLE的查询方法中的通知Uri。因此，只要任何表发生更改，就会通知相关游标。但有一个限制。也就是说，即使Article表中有变化，也会通知ARTICLES_USERS_JOIN_TABLE游标。

For tables, Users' andArticles', you can use their specific Uris for notification.

对于表格“用户”和“文章”，您可以使用其特定的Uris进行通知。

#1