PHP print_r清除mysqli连接对象的状态？

Question

I have a MySQL table where I require three columns to each be unique across the table, userName, userEmail and userUID. The table is set up with UNIQUE for each of these columns. In order to prevent race conditions I try a single insert of a new user and then pick up the 'duplicate entry' error, parse the error message to determine which column gave problems and then ask the user for new info. I was trying to debug this code and placed print_r($dbConn, true) to capture the outcome of the INSERT statemment before doing any of the tests for the duplicate column name. This broke things big time as it seemed to wipe out the errno and error values in the mysqli connection object. Here's a cut down sample that illustrates the problem:

<?php
    error_reporting(E_ALL);
    echo 'PHP Version: ' . phpversion() . PHP_EOL;
    $dbConn = @new mysqli('127.0.0.1', 'userX', 'passwordX', 'databaseX');
    $dbConn->query('CREATE TABLE IF NOT EXISTS print_r_test (' .
            'username VARCHAR(64), UNIQUE (username)');
    echo 'Created print_r_test table.' . PHP_EOL;
    $dbConn->query('TRUNCATE TABLE print_r_test');
    echo 'Truncated print_r_test table.' . PHP_EOL;
    $dbConn->query('INSERT INTO print_r_test (username) VALUES (\'testuser\')');
    echo '' . 'INSERT#1: ' . $dbConn->errno . ': ' . $dbConn->error . PHP_EOL;
    // This next one fails with duplicate entry 'testuser' for 'username'
    $dbConn->query('INSERT INTO print_r_test (username) VALUES (\'testuser\')');
//  echo '$dbConn: ' . print_r($dbConn, true) . PHP_EOL;
    echo '' . 'INSERT#2: ' . $dbConn->errno . ': ' . $dbConn->error . PHP_EOL;
?>

Note that line 14 is commented out.

If you run this as is (after changing userX, passwordX and databaseX) it works as expected:

H:>php print_r_test2.php
PHP Version: 5.4.10
Created print_r_test table.
Truncated print_r_test table.
INSERT#1: 0:
INSERT#2: 1062: Duplicate entry 'testuser' for key 'username'

The first INSERT at line 10 works and reports errno=0. The second insert fails with errno=1-62 and a message indicating the duplicate username.

Now, removing the //'s on line 14 so that the $dbConn contents are printed to the output and I get:

H:>php print_r_test2.php
PHP Version: 5.4.10
Created print_r_test table.
Truncated print_r_test table.
INSERT#1: 0:
$dbConn: mysqli Object
(
    [affected_rows] => -1
    [client_info] => mysqlnd 5.0.10 - 20111026 - $Id: b0b3b15c693b7f6aeb3aa66b646fee339f175e39 $
    [client_version] => 50010
    [connect_errno] => 0
    [connect_error] =>
    [errno] => 1062
    [error] => Duplicate entry 'testuser' for key 'username'
    [error_list] => Array
        (
            [0] => Array
                (
                    [errno] => 1062
                    [sqlstate] => 23000
                    [error] => Duplicate entry 'testuser' for key 'username'
                )

        )

    [field_count] => 0
    [host_info] => 127.0.0.1 via TCP/IP
    [info] =>
    [insert_id] => 0
    [server_info] => 5.6.19
    [server_version] => 50619
    [stat] => Uptime: 26920  Threads: 2  Questions: 97  Slow queries: 0  Opens: 85  Flush tables: 1  Open tables: 61  Queries per second avg: 0.003
    [sqlstate] => 00000
    [protocol_version] => 10
    [thread_id] => 20
    [warning_count] => 0
)

INSERT#2: 0:

The second INSERT reports 0 for OK but it clearly failed.

What seems to happen here is that the print_r($dbConn, true) results in the errno and error properties of the $dbConn conenction object being set to zero. That results in my code that looks for the 1062 error failing to find it.

If I leave the print_r line commented out and duplicate the INSERT#2 line then it prints out the 1062 error message twice.

If I duplicate the print_r line then I see the second one print out errno -> 0 and error is empty. What I have noticed is that the second one shows the Questions count in the connection stat has been increased by one. So my thinking is that the print_r of the $dbConn results in an additional query to MySQL which succeeds and returns 0 for OK and blows away the previous values in there.

This doesn't seem to be very helpful or is there something blindingly obvious that I'm missing here?

Thanks.

Following @Phil's comment below, my question is what am I doing wrong (if anything) that breaks the errno and error returns in the $dbConn object?

It's nothing to do with print_r . Replacing the last line with:

echo '' . 'INSERT#2: ' . $dbConn->errno . ': ' . $dbConn->error . PHP_EOL . $dbConn->stat . PHP_EOL;
echo '' . 'INSERT#2: ' . $dbConn->errno . ': ' . $dbConn->error . PHP_EOL . $dbConn->stat . PHP_EOL;

results in the output being:

INSERT#2: 1062: Duplicate entry 'testuser' for key 'username'
Uptime: 29364  Threads: 2  Questions: 136  Slow queries: 0  Opens: 91  Flush tables: 1  Open tables: 61  Queries per second avg: 0.004
INSERT#2: 0:
Uptime: 29364  Threads: 2  Questions: 137  Slow queries: 0  Opens: 91  Flush tables: 1  Open tables: 61  Queries per second avg: 0.004

Doing this:

echo '' . 'INSERT#2: ' . $dbConn->errno . ': ' . $dbConn->error . PHP_EOL;
echo '' . 'INSERT#2: ' . $dbConn->errno . ': ' . $dbConn->error . PHP_EOL;

results in:

INSERT#2: 1062: Duplicate entry 'testuser' for key 'username'
INSERT#2: 1062: Duplicate entry 'testuser' for key 'username'

If reading the connection object isn't an idempotent operation then that looks like a bear trap to me and the source of problems and frustration. So my question is, again, is there something that I'm doing wrong or missing or is this some strange feature of mysqli?

Answer 1

If you look at the documentation for mysqli->stat() , it is a function that executes a command 'mysqladmin status' on the server and returns whatever the server returns for that. If you look at the documentation for mysqli->errno you'll see that it "returns the error code for the most recent function call".

So what happens?

You execute your query, and you read the error code. Then you execute an other command that does not fail and you read the error code for that command. This is exactly what you should expect to happen.

---

If you need to value of errno or error after you call stat(), nothing prevents you from storing these values in a variable before you call stat():

$a = $dbConn->errno;
$b = $dbConn->error;
$c = $dbConn->stat();

echo $a . $b . $c;

Answer 2

It's an interesting question and I found out the answer after looking through the documentation: http://php.net/manual/en/class.mysqli.php

These are object properties: errno, error. Hence accessing them does not affect the state of the object.

On the other hand, stat() is a method call on the object. This means that errno and error will be updated to reflect whether that call succeeded or failed.