ActiveDataProvider::prepareModels: wrong queries when using union subqueries and pagination

[santilin]

What steps will reproduce the problem?

Create a query with a union subquery and use it with a paginated dataprovider:

$q1 = (new ActiveQuery())->from('my_table');
$q2 = (new ActiveQuery())->from('my_table');
$q1->andWhere(['id' => 2]);
$q2->andWhere(['user_id' => 4]);
$union = $this->union($q2);
// create a dataprovider with a pagination.
$d = new ActiveDataProvider( ['query' => $union, 'pagination' => .....] );
print_r ($d->getModels());

What is the expected result?

No errors should be reported.

What do you get instead?

SQLSTATE[HY000]: General error: 1 LIMIT clause should come after UNION not before
Failed to prepare SQL: SELECT "my_table".* FROM "my_table" WHERE ("my_table".id=:qp0) LIMIT 10 UNION SELECT "my_table".* FROM "my_table" WHERE ("my_table".user_id=:qp2)

The problem lies in ActiveDataProvider::prepareModels():

    if (($pagination = $this->getPagination()) !== false) {
        $pagination->totalCount = $this->getTotalCount();
        if ($pagination->totalCount === 0) {
            return [];
        }
        $query->limit($pagination->getLimit())->offset($pagination->getOffset());
    }

The $query->limit should take into account that if there is a union clause, that limit should be put in the last union query:

          if (count($query->union)>0) {
              $query->union[count($query->union)-1]['query']->limit($pagination->getLimit())->offset($pagination->getOffset());
         } else {
            $query->limit($pagination->getLimit())->offset($pagination->getOffset());
         }

There ara also lots of problems with orderBy clauses and unions, but all of them can be sorted out removing all the orderBy clauses and adding just one to the last union subquery, but it would be nice if Yii2 made it for us.

[santilin]

Working on this issue, I find impossible to use a union query for a gridview with an activecord, because when I click on the header of a cell to sort its contents, the orderby is added to the main query and I get the error:

SQLSTATE[HY000]: General error: 1 ORDER BY clause should come after UNION not before

Using Yii2.0.52-dev and php8.1 and mysql 8.0.39

[santilin]

The final function that fixes all these problems would be:

/**
 * {@inheritdoc}
 */
protected function prepareModels()
{
    if (!$this->query instanceof QueryInterface) {
        throw new InvalidConfigException('The "query" property must be an instance of a class that implements the QueryInterface e.g. yii\db\Query or its subclasses.');
    }
    $query = clone $this->query;

    $has_union = $query->union && count($query->union);
    if (($pagination = $this->getPagination()) !== false) {
        $pagination->totalCount = $this->getTotalCount();
        if ($pagination->totalCount === 0) {
            return [];
        }
        if ($has_union) {
            $query->union[count($query->union)-1]['query']->limit($pagination->getLimit())->offset($pagination->getOffset());
        } else {
            $query->limit($pagination->getLimit())->offset($pagination->getOffset());
        }
    }
    if (($sort = $this->getSort()) !== false) {
        $query->addOrderBy($sort->getOrders());
    }
    if ($has_union) {
        if ($query->orderBy) {
            $query->union[count($query->union)-1]['query']->addOrderBy($query->orderBy);
            $query->orderBy = null;
        }
    }

    return $query->all($this->db);
}

[samdark]

Do you have time for a pull request?

[santilin]

Sure, I'll do it ASAP.

[cepaim]

From which branch should I make the pr?
How can I add a tests for that pr?
Note: I'll do it under a different user: cepaim

[samdark]

master, just add test files.

[santilin]

Have a look at this pr: #20246