Added support for relations (#18)

README.md

@@ -164,6 +164,22 @@ $customers = Customer::query()
 
 See the `QueryBuilder` class for all available methods.
 
+## Relations
+
+Any relations published on a page can be accessed as well using the resource.
+
+```php
+$salesOrder = SalesOrder::query()->first();
+
+// Get the lines via the "relation" method.
+$salesLines = $salesOrder->relation('Relation_Name', SalesLine::class)->get();
+
+// Or use the "lines" helper on the SalesOrder.
+$salesLines = $salesOrder->lines('Relation_Name')->get();
+```
+
+Note that the `relation` method itself returns an instance of a query builder. This means that you can add additional where-clauses like you would be able to on a regular resource.
+
 ## Creating records
 
 Create a new record.

src/OData/BaseResource.php

@@ -144,6 +144,11 @@ public function newQuery(): QueryBuilder
         return new QueryBuilder($this->client(), $this->connection, $this->endpoint, static::class);
     }
 
+    public function relation(string $relation, string $class): QueryBuilder
+    {
+        return new QueryBuilder($this->client(), $this->connection, $this->getResourceUrl().'/'.$relation, $class);
+    }
+
     public static function fake(): void
     {
         foreach (config('dynamics.connections') as $connection => $data) {

src/OData/Pages/SalesOrder.php

@@ -3,11 +3,17 @@
 namespace JustBetter\DynamicsClient\OData\Pages;
 
 use JustBetter\DynamicsClient\OData\BaseResource;
+use JustBetter\DynamicsClient\Query\QueryBuilder;
 
 class SalesOrder extends BaseResource
 {
     public array $primaryKey = [
         'Document_Type',
         'No',
     ];
+
+    public function lines(string $relation): QueryBuilder
+    {
+        return $this->relation($relation, SalesLine::class);
+    }
 }