Exception thrown when merging: 'Error reading from database"

[bskamboj]

Please have a look below error message and let know me what is the issue and solution:
Exception thrown when merging: 'Error reading from database".
Unknown column 'id' in 'field list'
Trace:
#0 /var/www/html/moodle/lib/dml/mysqli_native_moodle_database.php(1247): moodle_database->query_end(false)
#1 /var/www/html/moodle/admin/tool/mergeusers/lib/table/generictablemerger.php(297): mysqli_native_moodle_database->get_records_sql('SELECT id FROM ...')
#2 /var/www/html/moodle/admin/tool/mergeusers/lib/table/generictablemerger.php(73): GenericTableMerger->get_records_to_be_updated(Array, 'userid')
#3 /var/www/html/moodle/admin/tool/mergeusers/lib/mergeusertool.php(268): GenericTableMerger->merge(Array, Array, Array)
#4 /var/www/html/moodle/admin/tool/mergeusers/lib/mergeusertool.php(192): MergeUserTool->_merge('13630', '17840')
#5 /var/www/html/moodle/admin/tool/mergeusers/index.php(135): MergeUserTool->merge('13630', '17840')
#6 {main}

Thank you

[Jordi Pujol-Ahulló]

Hi!

Thanks for reporting and detailing the error.

This kind of errors like Unknown column 'id' in 'field list' is produced when there are custom tables in the Moodle database that do not contain the id column.

Moodle forces by design that any table have to have an id column.

Therefore, if that table does not contain any user information, you can skip merging that table. An easy solution would be adding a custom config in the file config/config.local.php (create it if not exists, because it is not delivered with the plugin), and then put a content like this:

return array(
    'exceptions' => array (
        'your_table_name_with_no_id_column',
    ),
);

This content will be merged with the default config, and it will skip processing your table without id column.

Your task is to identify the table that does not contain the id column (it is no detailed in the stacktrace, unfortunately), and update the file config.local.php.

Give us feedback.

As always, try this in a testing environment first.

Regards,

Jordi

[Jordi Pujol-Ahulló]

I'm closing this issue.

[pmonty]

Hi @jpahullo, thought I might just post here since I experienced the exact same issue and resolved it (kind of with your fix).

I identified the table with no id column and added it to the array but now when I attempted to merge I get the following

Exception - Call to a member function merge() on null

Progress, but not sure why it is null

EDIT
Actually looks like this for loop in lib.php doesn't like it...

    foreach ($config->exceptions as $exception) {
        $options[$exception] = $exception;
    }

cause i get Warning: Invalid argument supplied for foreach() in

UPDATE
I carelessly forgot to put <?php at top of my file... so now it is

<?php

return array(
    'exceptions' => array (
        'mdl_auth_wncon_extdata',
    ),
);

despite this it now shows the original error error reading from database...

[pmonty]

Got it working after removing the mdl_ prefix on the table name :)

[Jordi Pujol-Ahulló]

Good to know! yes, table names have to not have the table prefix ;-)