Method readIndices

app/src/main/java/androidx/room/TableInfo.java:273–304

@return null if we cannot read the indices due to older sqlite implementations.

(SupportSQLiteDatabase database, String tableName)

     * @return null if we cannot read the indices due to older sqlite implementations.
     */
    @Nullable
    private static Set<Index> readIndices(SupportSQLiteDatabase database, String tableName) {
        Cursor cursor = database.query("PRAGMA index_list(`" + tableName + "`)");
        try {
            final int nameColumnIndex = cursor.getColumnIndex("name");
            final int originColumnIndex = cursor.getColumnIndex("origin");
            final int uniqueIndex = cursor.getColumnIndex("unique");
            if (nameColumnIndex == -1 || originColumnIndex == -1 || uniqueIndex == -1) {
                // we cannot read them so better not validate any index.
                return null;
            }
            HashSet<Index> indices = new HashSet<>();
            while (cursor.moveToNext()) {
                String origin = cursor.getString(originColumnIndex);
                if (!"c".equals(origin)) {
                    // Ignore auto-created indices
                    continue;
                }
                String name = cursor.getString(nameColumnIndex);
                boolean unique = cursor.getInt(uniqueIndex) == 1;
                Index index = readIndex(database, name, unique);
                if (index == null) {
                    // we cannot read it properly so better not read it
                    return null;
                }
                indices.add(index);
            }
            return indices;
        } finally {
            cursor.close();
        }
    }

    /**
     * @return null if we cannot read the index due to older sqlite implementations.