Improve the alias generator to create valid non numeric entries.

module/config/services.php

@@ -10,6 +10,7 @@
  */
 
 use Interop\Container\ContainerInterface;
+use Netzmacht\Contao\Leaflet\Alias\DefaultAliasFilter;
 use Netzmacht\Contao\Leaflet\Boot;
 use Netzmacht\Contao\Leaflet\ContaoAssets;
 use Netzmacht\Contao\Leaflet\Dca\ControlCallbacks;
@@ -138,7 +139,8 @@ $container[LeafletServices::ALIAS_GENERATOR] = $container->share(
             $filters = [
                 new ExistingAliasFilter(),
                 new SlugifyFilter($fields),
-                new SuffixFilter(false),
+                new DefaultAliasFilter($dataContainerName),
+                new SuffixFilter(),
             ];
 
             $validator = new UniqueDatabaseValueValidator(

src/Netzmacht/Contao/Leaflet/Alias/DefaultAliasFilter.php

@@ -0,0 +1,61 @@
+<?php
+
+/**
+ * @package    netzmacht
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2016 netzmacht David Molineus. All rights reserved.
+ * @filesource
+ *
+ */
+
+namespace Netzmacht\Contao\Leaflet\Alias;
+
+use Netzmacht\Contao\Toolkit\Data\Alias\Filter\AbstractFilter;
+
+/**
+ * Class DefaultAliasFilter creates an prefix of the alias.
+ *
+ * @package Netzmacht\Contao\Leaflet\Alias
+ */
+class DefaultAliasFilter extends AbstractFilter
+{
+    /**
+     * Alias prefix.
+     *
+     * @var string
+     */
+    private $prefix;
+
+    /**
+     * DefaultAliasFilter constructor.
+     *
+     * @param string $dataContainerName Data container name.
+     * @param int    $combine           Combine strategy.
+     */
+    public function __construct($dataContainerName, $combine = self::COMBINE_REPLACE)
+    {
+        parent::__construct(true, $combine);
+
+        $this->prefix = str_replace('tl_leaflet_', '', $dataContainerName);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function repeatUntilValid()
+    {
+        return false;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function apply($model, $value, $separator)
+    {
+        if (!$value) {
+            return $this->prefix . $separator . $model->id;
+        }
+
+        return $value;
+    }
+}