Merge pull request #2787 from zsilbi/relation-params-callback

Feature: callable relation params

en/db-models-relationships.md

@@ -301,6 +301,8 @@ Depending on the needs of our application we might want to store data in one tab
 
 Using relationships, you can get only those `Customers` that relate to our `Invoices` that have a certain `cst_status_flag`. Defining that constraint in the relationship allows you to let the model do all the work.
 
+It also accepts a closure, which is evaluated every time before the related records are accessed. This enables the conditions to be automatically updated between queries.
+
 ```php
 <?php
 
@@ -334,6 +336,27 @@ class Invoices extends Model
                 ]
             ]
         );
+
+        $container = $this->getDI();
+
+        $this->hasMany(
+            'inv_cst_id',
+            Customers::class,
+            'cst_id',
+            [
+                'reusable' => true,
+                'alias'    => 'customersNearby',
+                'params'   => function() use ($container) {
+                    return [
+                        'conditions' => 'cst_location = :location:',
+                        'bind'       => [
+                            // Location can change between queries
+                            'location' => $container->getShared('myLocationService')->myLocation,
+                         ]
+                    ];
+                }
+            ]
+        );
     }
 }
 ```