Ensure that only one typecaster is attached.

If multiple type casters are attached we waste cycles. More importantly,
we also cause fatal errors for folks loading datetimes in non-english
locales.

Refs #8157

src/Database/Query.php

@@ -129,6 +129,13 @@ class Query implements ExpressionInterface, IteratorAggregate
      */
     protected $_selectTypeMap;
 
+    /**
+     * Tracking flag to ensure only one type caster is appended.
+     *
+     * @var bool
+     */
+    protected $_typeCastAttached = false;
+
     /**
      * Constructor.
      *
@@ -183,8 +190,9 @@ public function execute()
         $driver = $this->_connection->driver();
         $typeMap = $this->selectTypeMap();
 
-        if ($typeMap->toArray()) {
+        if ($typeMap->toArray() && $this->_typeCastAttached === false) {
             $this->decorateResults(new FieldTypeConverter($typeMap, $driver));
+            $this->_typeCastAttached = true;
         }
 
         $this->_iterator = $this->_decorateStatement($statement);
@@ -1630,6 +1638,7 @@ public function decorateResults($callback, $overwrite = false)
     {
         if ($overwrite) {
             $this->_resultDecorators = [];
+            $this->_typeCastAttached = false;
         }
 
         if ($callback !== null) {

tests/TestCase/Database/QueryTest.php

@@ -3547,7 +3547,6 @@ public function testSelectTypeMap()
     public function testSelectTypeConversion()
     {
         $query = new Query($this->connection);
-        $time = new \DateTime('2007-03-18 10:50:00');
         $query
             ->select(['id', 'comment', 'the_date' => 'created'])
             ->from('comments')

tests/TestCase/ORM/QueryTest.php

@@ -3197,4 +3197,25 @@ public function testNotMatchingNested()
         ];
         $this->assertEquals($expected, $results->first());
     }
+
+    /**
+     * Test that type conversion is only applied once.
+     *
+     * @return void
+     */
+    public function testAllNoDuplicateTypeCasting()
+    {
+        $table = TableRegistry::get('Comments');
+        $query = $table->find()
+            ->select(['id', 'comment', 'created']);
+
+        // Convert to an array and make the query dirty again.
+        $result = $query->all()->toArray();
+        $query->limit(99);
+
+        // Get results a second time.
+        $result2 = $query->all()->toArray();
+
+        $this->assertEquals(1, $query->__debugInfo()['decorators'], 'Only one typecaster should exist');
+    }
 }