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Commit 0ba1cb06 authored by Tom O'Neill's avatar Tom O'Neill
Browse files

ContentResolver.query() includes performance considerations 

Mention the desirability of using "?"-substitution in the where clause,
and reemphasize the importance of using an explicit projection.

Change-Id: Iaa489d50db409f34e78bcd55253e5a4e53445cf2
parent d1265feb

core/java/android/content/ContentResolver.java

+28 −16
Original line number Diff line number Diff line
@@ -173,13 +173,25 @@ public abstract class ContentResolver { 
    }



    /**

     * <p>

     * Query the given URI, returning a {@link Cursor} over the result set.

     * </p>

     * <p>

     * For best performance, the caller should follow these guidelines:

     * <ul>

     * <li>Provide an explicit projection, to prevent

     * reading data from storage that aren't going to be used.</li>

     * <li>Use question mark parameter markers such as 'phone=?' instead of

     * explicit values in the {@code selection} parameter, so that queries

     * that differ only by those values will be recognized as the same

     * for caching purposes.</li>

     * </ul>

     * </p>

     *

     * @param uri The URI, using the content:// scheme, for the content to

     *         retrieve.

     * @param projection A list of which columns to return. Passing null will

     *         return all columns, which is discouraged to prevent reading data

     *         from storage that isn't going to be used.

     *         return all columns, which is inefficient.

     * @param selection A filter declaring which rows to return, formatted as an

     *         SQL WHERE clause (excluding the WHERE itself). Passing null will

     *         return all rows for the given URI.