try

class/espece.php

@@ -2,6 +2,7 @@
 
 class Espece extends Objet
 {
+    protected $_primaryAttr = "nom";
     protected $nom;
     protected $prix_consultation;
 

class/objet.php

@@ -129,8 +129,8 @@ class Objet
         $dbName = self::dbName();
         $bdd = new Db();
 
-        $requete_prepare = $bdd->db->prepare("SELECT * FROM ".$dbName." WHERE ".$this->_primaryAttr." = :".$this->getAll()[0]); // on prépare notre requête
-        $requete_prepare->execute(array("{$this->getAll()[0]}" => $id));
+        $requete_prepare = $bdd->db->prepare("SELECT * FROM ".$dbName." WHERE ".$this->_primaryAttr." = :id"); // on prépare notre requête
+        $requete_prepare->execute(array("id" => $id));
 
         $ligne = $requete_prepare->fetch(PDO::FETCH_ASSOC);
         $this->fromDb($ligne);

class/race.php

@@ -2,6 +2,7 @@
 
 class Race extends Objet
 {
+    protected $_primaryAttr = "nom";
     protected $nom;
     protected $espece;
     protected $prix_intervention;