Adds exists rule for relation key validation

Author: Mark Salmon

src/Translators/Rules.php

@@ -46,6 +46,11 @@ public static function fromColumn(Column $column, string $context = null)
             if (Str::startsWith($column->dataType(), 'unsigned')) {
                 $rules = array_merge($rules, ['gt:0']);
             }
+
+            if (Str::endsWith($column->name(), '_id')) {
+                [$table, $field] = explode('_', $column->name());
+                $rules = array_merge($rules, ['exists:' . Str::plural($table) . ',' . $field]);
+            }
         }
 
         if (in_array($column->dataType(), [

tests/Feature/Translators/RulesTest.php

@@ -90,8 +90,19 @@ public function forColumn_returns_numeric_rule_for_numeric_types($data_type)
     public function forColumn_returns_integer_rule_for_integer_types($data_type)
     {
         $column = new Column('test', $data_type);
+        $this->assertContains('integer', Rules::fromColumn($column));
+    }
+
+    /**
+     * @test
+     * @dataProvider integerDataTypesProvider
+     */
+    public function forColumn_returns_exists_rule_for_foreign_keys($data_type)
+    {
+        $column = new Column('test_id', $data_type);
 
         $this->assertContains('integer', Rules::fromColumn($column));
+        $this->assertContains('exists:tests,id', Rules::fromColumn($column));
     }
 
     /**