Develop Reference

How to filter content resolver query results in android? Passing selection parameter still doesn't work

I'm trying to filer out city names and return matching cities based on the selection parameter being passed.
However the query call still returns all the rows. Even tried putting in a fake city name that doesn't already exist in the database and it still spits out the same original rows.
public void addLocation(String cityName){
Cursor cursor = mContext.getResolver().query(
WeatherContract.LocationEntry.CONTENT_URI,
null,
WeatherContract.LocationEntry.COLUMN_LOCATION_SETTING +
" = " + cityName,
null,
null);
I've read the Android docs over and over, ContentResolver Query, and passing the selection parameter in doesn't seem to be doing anything.
public final Cursor query (Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder)

Assuming the provider you're using is androidx.core.content.FileProvider (according to what you've declared in your manifest), the selection, selectionArgs and sortOrder parameters of FileProvider.query are... ignored in AndroidX's implementation !
See the v1.2.0 source here (line 409)
The only solution I found is to filter and sort the results post-query, in your own code.
And yeah, that's kinda sad...

Instead of passing the value in the selection parameter, put it in selectionArgs.
public void addLocation(String cityName){
String[] args = { cityName };
Cursor cursor = mContext.getResolver().query(
WeatherContract.LocationEntry.CONTENT_URI,
null,
WeatherContract.LocationEntry.COLUMN_LOCATION_SETTING +
" = ?",
args,
null);

How to use selection args to query specific rows from a contentprovider in android

i have constructed a basic content provider that stores SMS messages for learning purposes, so far i can read(without selection args), insert, update and delete.
However i have been stumped trying to figure out how to format the selection args for the WHERE clause in my provider:
Basicly my application needs to search for a specific timestamp (in long format) and return its _id
say your database has an entry like this that your trying to access:
2|1|1410293471300|test type 1||testing|0
and the entire database looks like this:
_id|CLIENTTRXID|CREATED_AT|TYPE|MESSAGEPRIO|MESSAGE|ACCEPTED
1|1|1410293471000|test type 1||testing|0
2|1|1410293471300|test type 1||testing|0
3|1|1410293471600|test type 1||testing|0
in sql the query would be
"select _id from alerts where CREATED_AT=1410293471300;"
the code i was hoping would do the equivalent:
//normally i would get the string dynamically but to make it equal to the sql
String date = "1410293471300";
String[] selectionArgs = new String[]{ date };
Cursor cursor = getContext().getContentResolver().query(AlertContract.CONTENT_URI, null, AlertContract.Column.CREATED_AT, selectionArgs, AlertContract.DEFAULT_SORT);
seems to always produce the following error no matter what i try as selectionArgs
Exception caught﹕ Cannot bind argument at index 1 because the index is out of range. The statement has 0 parameters.
here is the query method of my contentprovider:
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
qb.setTables( AlertContract.TABLE);
switch (sURIMatcher.match(uri)) {
case AlertContract.STATUS_DIR:
break;
case AlertContract.STATUS_ITEM:
qb.appendWhere(AlertContract.Column.ID + "=" + uri.getLastPathSegment());
break;
default:
throw new IllegalArgumentException( "illegal uri: " + uri);
}
String orderBy = (TextUtils.isEmpty(sortOrder)) ? AlertContract.DEFAULT_SORT : sortOrder;
SQLiteDatabase db = dbHelper.getReadableDatabase();
Cursor cursor = qb.query(db, projection, selection, selectionArgs, null, null, orderBy);
//register for uri changes
cursor.setNotificationUri(getContext().getContentResolver(), uri);
Log.d(TAG, "queried records: "+cursor.getCount());
return cursor;
}
Presumably im missing something extremely obvious, and will feel quite silly for having posted this question.
But for the moment i would very much appreciate any help, as i am quite stumped.

It looks like your issue is with your selection, rather than with your selectionArgs per se. The selection should be the whole query after the "where". Here your selection is "CREATED_AT". You need two more items to get it to work:
an =, since you want equality (you can also do other operators, of course)
a ?. This is where your selectionArgument will be inserted (each argument needs a ? in the selection, so there should be the same number of ?s in the selection as selectionArguments.
The end result should be more like "CREATED_AT = ?"
Check out the documentation and this tutorial for more info on how to correctly construct a ContentProvider query.

When you query the content provider, try the following. The selection should be AlertContract.Column.CREATED_AT + "=?"
Cursor cursor = getContext().getContentResolver().query(AlertContract.CONTENT_URI, null, AlertContract.Column.CREATED_AT + "=?", selectionArgs, AlertContract.DEFAULT_SORT);

Cursorloader not refreshing when underlying data changes

I have a content provider, a content resolver, and a cursor loader. The loader is used to indirectly populate a listview (ie not a simple cursor adapter, rather an array adapter, since I need to use the cursor's results to gather other data).
When I change the underlying data, the listview does not re-populate as the onLoadFinished(Loader<Cursor>, Cursor) call back is not called.
As suggested while I'm writing this, there are a lot of questions on this issue.
eg
CursorLoader not updating after data change
And all the questions point out two things:
In your content provider query() method, you need to tell the cursor about notifications a'la
c.setNotificationUri(getContext().getContentResolver(), uri);
In your content provider insert/update/delete method, you need to notify on the URI:
getContext().getContentResolver().notifyChange(uri, null);
I'm doing those things.
I'm also NOT closing any of the cursors I get back.
Note, my content provider lives in a separate app (think of it as a content provider app -- no launcher main activity). A com.example.provider APK, and the com.example.app is calling (in the content resolver) via the content://com.example.provider/table URI etc. The content resolver (dbhelper) lives in a library project (com.example.appdb) that the activity links in. (This way, multiple projects can use the dbhelper via linking, and all content providers are installed via single APK)
I have turned on debugging in the loader manager, and can see where I force a refresh after the data changes (ie the loader being restarted and previous being marked inactive), but nothing that says anything is happening automatically -- rather, in response to my force refresh.
Any ideas why my loader isn't being refreshed ?
-- EDIT --
The loader create:
Log.d(TAG, "onCreateLoader ID: " + loaderID);
// typically a switch on the loader ID, and then
return dbHelper.getfoo()
Where getfoo() returns a cursor loader via:
return new CursorLoader(context, FOO_URI, foo_Fields, foo_query, foo_argArray, foo_sort );
Loader Finish takes the cursor and populates a table (and does some processing) -- nothing fancy there.
public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
Log.d(TAG, "onLoadFinished id: " + loader.getId());
// switch on loader ID ..
FillTable(cursor, (FooAdapter) foo_info.listview.getAdapter();
Loader Reset clears the table.
public void onLoaderReset(Loader<Cursor> loader) {
Log.d(TAG, "onLoaderReset id: " + loader.getId());
// normally a switch on loader ID
((FooAdapter)foo_info.listview.getAdapter()).clear();
The content provider does:
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
Cursor cursor;
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
SQLiteDatabase db = dbHelper.getReadableDatabase();
switch (sUriMatcher.match(uri)) {
case FOO:
qb.setTables(FOO);
qb.setProjectionMap(FooProjectionMap);
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, sortOrder);
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}
Then insert/update is similar:
public Uri insert(Uri uri, ContentValues initialValues) {
ContentValues values;
if (initialValues != null) {
values = new ContentValues(initialValues);
} else {
values = new ContentValues();
}
String tableName;
Uri contentUri;
switch (sUriMatcher.match(uri)) {
case FOO:
tableName = FOOTABLE;
contentUri = FOO_URI;
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
SQLiteDatabase db = dbHelper.getWritableDatabase();
long rowId = db.insert(tableName, null, values);
if (rowId > 0) {
Uri objUri = ContentUris.withAppendedId(contentUri, rowId);
getContext().getContentResolver().notifyChange(objUri, null);
return objUri;
}
throw new SQLException("Failed to insert row into " + uri);
}

I see that you aren't calling swapCursor or changeCursor in your onLoadFinished and onLoaderReset. You need to do that for your adapter to access the data loaded into the new cursor.
in onLoadFinished, call something like:
mAdapter.swapCursor(cursor)
In onLoaderReset, call this to remove references to the old cursor:
mAdapter.swapCursor(null)
Where mAdapter is your listView's adapter.
More info: http://developer.android.com/guide/components/loaders.html#onLoadFinished

So, for anyone who looks this up and has this problem:
Make certain that the URI you register the cursor on, and the URI you notify the cursor on are the same.
In my case, I was using a different URI to query than was used in other code that modified the underlying table. There wasn't an easy fix to make notification work, so I kept resetting the loader in OnResume() as the solution.

This is not a direct answer to this specific problem, but may help others in a similar situation. In my case, I had a join and even though I used the full tablename.columnname in the projection and query. It ended up using the wrong ID values anyway. So be sure to check your ContentProvider or SQL syntax.

GROUP BY with CursorLoader

How do I define a GROUP BY query for my CursorLoader?
The two constructors for a CursorLoader I see take either a single Context or a Context, Uri, projection, selection, selectionArgs and sortOrder.
But no groupBy.
(I'm using the support package for a Android 2.3 device)

Not really...
You can define a specific URI to your specific GROUP BY clause.
For example, if you have a table mPersonTable, possibly grouped by gender, you can define the following URIs:
PERSON
PERSON/#
PERSON/GENDER
When querying, switch between your queries so you can add your group by parameter:
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
String groupBy = null;
switch (mUriMatcher.match(uri)) {
case PERSON_ID:
...
break;
case PERSON_GENDER:
groupBy = GENDER_COLUMN;
case PERSON:
SQLiteQueryBuilder builder = new SQLiteQueryBuilder();
builder.setTables(mPersonTable);
builder.setProjectionMap(mProjectionMap);
return builder.query(db, projection, selection, selectionArgs, groupBy, having, sortOrder, limit);
default:
break;
}
}
In fact, you could pass any sort of parameters to your query
Obs.: Use a UriMatcher to match the uri with your query implementation.

You can add Group by with selection parameter
new CursorLoader(context,URI,
projection,
selection+") GROUP BY (coloum_name",
null,null);

Apparently (and this is a bit embarrassing) the very first line in the documentation clearly states that the CursorLoader queries the ContentResolver to retrieve the Cursor. While the ContentResolver doesn't expose any means to GROUP BY there is, hence, no way the CursorLoader could expose such functionality either.
So the apparent answer to my very own question is: You can't!

How do I get the _count in my content provider?

What should I do to get my content provider to return the _count column with the count of records? The documentation says it is automatic, but maybe it's only taking about some built-in content provider. Running a query to the database seems not to return it.

If you are using contentProvider then you have to do it like count(*) AS count.
If you use cursor.getCount(), that would not be as efficient as the above approach. With cursor.getCount() you are fetching all the records just to get counts. The entire code should look like following -
Cursor countCursor = getContentResolver().query(CONTENT_URI,
new String[] {"count(*) AS count"},
null,
null,
null);
countCursor.moveToFirst();
int count = countCursor.getInt(0);
The reason why this works is because android needs a column name to be defined.

If you are using ContentProvider.query() a Cursor is returned. Call Cursor.getCount() to get a count of records in the returned cursor.

I had a similiar problem and found this worked for me. In the example below I wanted to get the count of images from the MediaStore provider.
final String[] imageCountProjection = new String[] {
"count(" + MediaStore.Images.ImageColumns._ID + ")",
};
Cursor countCursor = getContentResolver().query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
imageCountProjection,
null,
null,
null);
countCursor.moveToFirst();
int existingImageCount = countCursor.getInt(0);

With cursor.getCount() you can not assure that it returns the real number of items returned. There are much better ways:
1- If you are using Content Providers, you can do a query and use the Column (_COUNT) included in BaseColumns for your projection
#Override
public Cursor query(SQLiteDatabase db, Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
...
projection = new String[] {
ContentContract.NotificationCursor.NotificationColumns._COUNT,
};
...
Cursor cursor = queryBuilder.query(db, projection, selection, selectionArgs, groupBy, having, sortOrder);
return cursor;
}
2- To do a rawQuery using SELECT COUNT(*) as #saurabh says in his response.