无法通过两种不同的方法循环结果集

Question

I have ran in to a pickle with using a while loop to iterate over a result set.

I execute a query, and pass into a class, storing it as a private variable.

Then I use two separate methods to do a while loop over the result set.

The first method works, the second doesn't.

Here's some code to show example.

<?php

class DataFlow {

    private $resultSet;

    function __construct($results) {
        $this->resultSet = $results;
    }

    function method1() {
        while ($rows = CDB::GetAssoc($this->resultSet)) {
            // works here
            echo $rows;
        }
    }

    function method2() {
        while ($rows = CDB::GetAssoc($this->resultSet)) {
            // doesn't work here 
            echo $rows;
        }
    }

}

$sqlQuery = "....";
$results = CDB::ExecuteQuery($sql);
$dataFlow = new DataFlow($results);

echo $dataflow->method1(); // Works
echo $dataflow->method2(); // Doesn't work.
?>

Now if I edit this to include the query execution locally.. it works

<?php

class DataFlow {

    private $resultSet;

    function __construct($results) {
        $this->resultSet = $results;
    }

    function method1() {
        while ($rows = CDB::GetAssoc($this->resultSet)) {
            // works here
            echo $rows;
        }
    }

    function method2() {
        $sqlQuery = "....";
        $results = CDB::ExecuteQuery($sql);

        while ($rows = CDB::GetAssoc($results)) {
            // now works here 
            echo $rows;
        }
    }

}

$sqlQuery = "....";
$results = CDB::ExecuteQuery($sql);
$dataFlow = new DataFlow($results);

echo $dataflow->method1(); // Works
echo $dataflow->method2(); // Works
?>

I can't seem to figure out why I can't use a result set twice in the same class. Any ideas?

Answer 1

reading results from a database query involves iterating over some kind of a cursor going through the result rows. Depending on your database class, you might be able to reset this cursor to loop over the results several times if needed. If not, then you would have to perform the query again.