INSERT not complete before SELECT query - php

Question

I have a PHP script that is split into two separate PHP scripts (As they each serve a purpose and are quite lengthy). For simplicity let's call these 1.php and 2.php.
Script 1.php does an API call to a website passes the payload to a function. Once has truncated and inserted the new records into the table, it then includes the 2nd script. This is where the issue begins. Seemingly when I query the marketPlace table it returns a null array however if I insert a sleep(1) before I include 2.php it works! I can only summize that somehow the truncate and insert queries in 1.php had not completed before the next queries were called? (I've never come across this before!).
There is only one database connection and is defined by a database class which is contained in 1.php:
class Database
{
// This class allows us to access the database from any function with ease
// Just call it with Database::$conn
/** TRUE if static variables have been initialized. FALSE otherwise
*/
private static $init = FALSE;
/** The mysqli connection object
*/
public static $conn;
/** initializes the static class variables. Only runs initialization once.
* does not return anything.
*/
public static function initialize()
{
Global $servername;
Global $username;
Global $password;
Global $dbname;
try {
if (self::$init===TRUE)return;
self::$init = TRUE;
self::$conn = new mysqli($servername, $username, $password, $dbname);
}
catch (exception $e) {
date('Y-m-d H:i:s',time()) . " Cant' connect to MySQL Database - re-trying" . PHP_EOL;
}
}
public static function checkDB()
{
if (!mysqli_ping(self::$conn)) {
self::$init = FALSE;
self::initialize();
}
}
}
The function that trunctated and inserted into the marketplace is:
function processMarketplace($marketData) {
// Decode to JSON
$outputj = json_decode($marketData, true);
$marketplaceCounter = 0;
// Check for success
if (($outputj['success']==true) && (!stristr($marketData, "error"))) {
// Create the blank multiple sql statement
$sql = "TRUNCATE marketplace;"; // Clears down the current marketPlace table ready for new INSERTS
//Loop through each multicall
foreach ($outputj['multiCall'] as $orderBook) {
foreach ($orderBook['marketplace'] as $orderLine) {
$type = $orderLine['type'];
$price = $orderLine['amountCurrency'];
// Add new SQL record (This ignores any duplicate values)
$sql .="INSERT IGNORE INTO marketplace (type, price) VALUES ('" . $type . "'," . $price . ");";
}
$marketplaceCounter++;
}
// Now run all the SQL's to update database table
if (strlen($sql) > 0) {
if (Database::$conn->multi_query($sql) === TRUE) {
echo mysqli_error(Database::$conn);
//echo "New records created successfully";
} else {
echo mysqli_error(Database::$conn);
echo "Error: " . $sql . "<br>" . Database::$conn->error;
}
}
echo date('Y-m-d H:i:s',time()) . " == Marketplace Orderbook retreived == <BR><BR>" . PHP_EOL;
} else {
echo date('Y-m-d H:i:s',time()) . " Failed to get Marketplace data. Output was: " . $marketData . "<BR>" . PHP_EOL;
die();
}
}
I've chased this around for hours and hours and I really don't understand why adding the sleep(1) delay after I have called the processMarketplace() function helps. I've also tried merging 1.php and 2.php together as one script and this yields the same results. 2.php simply does a SELECT * FROM marketPlace query and this returns NULL unless i have the sleep(1).
Am I missing something easy or am I approaching this really badly?
I should add I'm using InnoDB tables.
This is how its called in 1.php:
$marketData = getData($user,$api); // Get Marketplace Data
processMarketplace($marketData); // Process marketplace data
sleep(1); // Bizzare sleep needed for the select statement that follows in 2.php to return non-null
include "2.php"; // Include 2nd script to do some select statements on marketPlace table
2.php contains the following call:
$typeArray = array('1','2','3');
foreach ($typeArray as $type) {
initialPopulate($type);
}
function initialPopulate($type) {
// Reset supplementary prices
mysqli_query(Database::$conn, "UPDATE marketPlace SET price_curr = '999999' WHERE type='" . $type . "'");
echo mysqli_error(Database::$conn);
// Get marketplace data <--- This is the one that is strangely returning Null (after the first loop) unless I place the sleep(1) before including 1.php
$query = "SELECT * FROM marketPlace WHERE type='" . $type . "'";
$result = mysqli_query(Database::$conn, $query);echo mysqli_error(Database::$conn);
$resultNumRows = mysqli_num_rows($result);echo mysqli_error(Database::$conn);
// Create array from mysql data
$rows = array();
while($r = mysqli_fetch_assoc($result)) {
$rows[] = $r;
}
// Get information from the offertypes table
$query2 = "SELECT offerID FROM queryTypes WHERE type='" . $type . "'";
$result2 = mysqli_query(Database::$conn, $query2);echo mysqli_error(Database::$conn);
// Create array from mysql data
$rows2 = array();
while($r2 = mysqli_fetch_row($result2)) {
$rows2[] = $r2;
}
// Loop through marketplace data and apply data from the offertypes table
$sql1 = ""; // Create a blank SQL array that we will use to update the database
$i = 0;
foreach ($rows as $row) {
$sql1 .= "UPDATE marketPlace SET enrichmentType = " . $rows2[$i][0] . " WHERE type='" . $type . "';";
$i++;
}
// Now run all the SQL's to update database table
if (strlen($sql1) > 0) {
if (Database::$conn->multi_query($sql1) === TRUE) {
echo mysqli_error(Database::$conn);
//echo "New records created successfully";
} else {
echo mysqli_error(Database::$conn);
echo "Error: " . $sql1 . "<br>" . Database::$conn->error;
}
}
}

Answer 1

You are using mysqli:multi_query.
Unlike query, multi_query does not retrieve the results immediately. Retrieving the results must be done using mysqli::use_result
An example from the documentation:
/* execute multi query */
if ($mysqli->multi_query($query)) {
do {
/* store first result set */
if ($result = $mysqli->use_result()) {
while ($row = $result->fetch_row()) {
printf("%s\n", $row[0]);
}
$result->close();
}
/* print divider */
if ($mysqli->more_results()) {
printf("-----------------\n");
}
} while ($mysqli->next_result());
}
You don't need to print the results, but if you don't retrieve them, you are not guaranteed the INSERT has completed.
Note in the documentation for use_result at
https://www.php.net/manual/en/mysqli.use-result.php
it states
"Either this or the mysqli_store_result() function must be called
before the results of a query can be retrieved, and one or the other
must be called to prevent the next query on that database connection
from failing."
As a result of not calling store_result or use_result, you are having unpredictable results.