perf: improve mapping lookup performance

mapping-experiment.php

@@ -0,0 +1,168 @@
+<?php declare(strict_types=1);
+
+// Todo: do not merge this experiment
+
+/**
+ * A task that holds a reference to a string and the source id of the mapping
+ *
+ * It makes it possible to update the referenced string at a later point
+ */
+class MappingTask
+{
+    public function __construct(
+        public string &$reference,
+        public string $sourceId
+    ) {
+    }
+}
+
+class MappingService
+{
+    /**
+     * @var list<MappingTask>
+     */
+    private array $pendingTasks = [];
+
+    /**
+     * Important: this method returns a reference to a string which is also internally stored.
+     * It must be called like this:
+     *
+     * $data['someId'] = &$mappingService->getMapping('sourceId');
+     *
+     * The use of '&' is very important, otherwise it will only copy the placeholder string.
+     * More info on this can be found in the PHP docs:
+     * https://www.php.net/manual/en/language.references.return.php
+     */
+    public function &getMapping(string $sourceId): string
+    {
+        // previously we would fetch the mapping from the DB here,
+        // but reaching out to the DB every time is expensive
+
+        // so instead we just return a placeholder string
+        // and update it later, when we know all mappings that are needed
+
+        // and then use the string reference to update the placeholders
+
+        $pointer = 'placeholder-mapping-uuid';
+
+        $task = new MappingTask($pointer, $sourceId);
+        $this->pendingTasks[] = $task;
+
+        return $pointer;
+    }
+
+    public function resolvePendingMappings(): void
+    {
+        // in here we can fetch all requested mappings from the DB
+        // in a single query and update all corresponding strings
+        foreach ($this->pendingTasks as $task) {
+            $task->reference = 'changed-' . $task->sourceId;
+            unset($task->reference);
+        }
+    }
+}
+
+// a stripped-down example of a converter
+function convertData(MappingService $mappingService): array
+{
+    $data['name'] = 'John Doe';
+    $data['manufacturerId'] = &$mappingService->getMapping('manufacturer01');
+    $data['price'] = [];
+    for ($i = 0; $i < 3; ++$i) {
+        $data['price'][] = convertCurrency($i, $mappingService);
+    }
+
+    return $data;
+}
+
+// a stripped-down example of internal logic in a converter
+function convertCurrency(int $i, MappingService $mappingService): array
+{
+    $price = [
+        'id' => $i,
+        // unfortunately, this does not work, but there is an easy workaround below
+        // 'currencyId' => &$mappingService->getMapping('currency0' . $i),
+    ];
+
+    // this works fine
+    $price['currencyId'] = &$mappingService->getMapping('currency0' . $i);
+
+    return $price;
+}
+
+// === Main logic below ===
+
+$mappingService = new MappingService();
+$convertedData = convertData($mappingService);
+echo '============== Initial data after converter run ==============' . \PHP_EOL;
+var_dump($convertedData);
+
+echo '============== data after mapping tasks got resolved ==============' . \PHP_EOL;
+$mappingService->resolvePendingMappings();
+var_dump($convertedData);
+
+// === Output looks like this ===
+/*
+============== Initial data after converter run ==============
+array(3) {
+  ["name"]=>
+  string(8) "John Doe"
+  ["manufacturerId"]=>
+  &string(24) "placeholder-mapping-uuid"
+  ["price"]=>
+  array(3) {
+    [0]=>
+    array(2) {
+      ["id"]=>
+      int(0)
+      ["currencyId"]=>
+      &string(24) "placeholder-mapping-uuid"
+    }
+    [1]=>
+    array(2) {
+      ["id"]=>
+      int(1)
+      ["currencyId"]=>
+      &string(24) "placeholder-mapping-uuid"
+    }
+    [2]=>
+    array(2) {
+      ["id"]=>
+      int(2)
+      ["currencyId"]=>
+      &string(24) "placeholder-mapping-uuid"
+    }
+  }
+}
+============== data after mapping tasks got resolved ==============
+array(3) {
+  ["name"]=>
+  string(8) "John Doe"
+  ["manufacturerId"]=>
+  string(22) "changed-manufacturer01"
+  ["price"]=>
+  array(3) {
+    [0]=>
+    array(2) {
+      ["id"]=>
+      int(0)
+      ["currencyId"]=>
+      string(18) "changed-currency00"
+    }
+    [1]=>
+    array(2) {
+      ["id"]=>
+      int(1)
+      ["currencyId"]=>
+      string(18) "changed-currency01"
+    }
+    [2]=>
+    array(2) {
+      ["id"]=>
+      int(2)
+      ["currencyId"]=>
+      string(18) "changed-currency02"
+    }
+  }
+}
+ */