Add withOneByJoin method

src/Definition.php

@@ -134,6 +134,27 @@ public function withMany(Definition $definition, string $name, string $foreignCo
         return $this;
     }
 
+    /**
+     * Adds a one-to-one relationship through a joined table.
+     *
+     * @param Definition $definition
+     * @param string $name
+     * @param string $foreignColumn
+     * @param string $localColumn
+     * @param string $joinTable
+     * @param string $joinForeignColumn
+     * @param string $joinLocalColumn
+     * @return Definition
+     */
+    public function withOneByJoin(Definition $definition, string $name, string $foreignColumn, string $localColumn, string $joinTable, string $joinForeignColumn, string $joinLocalColumn)
+    {
+        $property = new Property($name, false, $definition, $localColumn, $foreignColumn);
+        $property->join($joinTable, $joinLocalColumn, $joinForeignColumn);
+
+        $this->properties[] = $property;
+        return $this;
+    }
+
     /**
      * Adds a one-to-many relationship through a joined table.
      *

tests/Fixtures.sql

@@ -14,6 +14,9 @@ CREATE TABLE discounts (id INTEGER PRIMARY KEY, order_id INTEGER, description TE
 DROP TABLE IF EXISTS orders_fulfillments;
 CREATE TABLE orders_fulfillments (order_id INTEGER, employee_id INTEGER);
 
+DROP TABLE IF EXISTS employees;
+CREATE TABLE employees (id INTEGER PRIMARY KEY, name TEXT);
+
 -- Seed database
 INSERT INTO customers (id, name) VALUES
 (1, 'John Doe'),
@@ -34,3 +37,11 @@ INSERT INTO items (id, order_id, description, amount) VALUES
 
 INSERT INTO discounts (id, order_id, description, amount) VALUES
 (1, 2, '$10', 10);
+
+INSERT INTO employees (id, name) VALUES
+(1, 'Alice'),
+(2, 'Bob');
+
+INSERT INTO orders_fulfillments (order_id, employee_id) VALUES
+(1, 1),
+(2, 2);

tests/MappingTest.php

@@ -560,6 +560,51 @@ public function testFindOneWithDirectAndSecondaryLeft()
         $this->assertEquals(400, $customer['orders'][0]['items'][1]['amount']);
     }
 
+    public function testFindAllWithOneByJoin()
+    {
+        $orders = $this->getWithOneByJoinMapping()->findAll();
+
+        $this->assertCount(3, $orders);
+
+        $this->assertEquals('Alice', $orders[0]['employee']['name']);
+        $this->assertEquals('Bob', $orders[1]['employee']['name']);
+        $this->assertNull($orders[2]['employee']);
+    }
+
+    public function testFindOneWithOneByJoin()
+    {
+        $order = $this->getWithOneByJoinMapping()->eq('id', 2)->findOne();
+
+        $this->assertNotNull($order);
+        $this->assertEquals(2, $order['id']);
+        $this->assertEquals('Bob', $order['employee']['name']);
+    }
+
+    public function testFindAllWithManyByJoin()
+    {
+        $employees = $this->getWithManyByJoinMapping()->findAll();
+
+        $this->assertCount(2, $employees);
+
+        $this->assertEquals('Alice', $employees[0]['name']);
+        $this->assertCount(1, $employees[0]['orders']);
+        $this->assertEquals('2018-01-01', $employees[0]['orders'][0]['date_created']);
+
+        $this->assertEquals('Bob', $employees[1]['name']);
+        $this->assertCount(1, $employees[1]['orders']);
+        $this->assertEquals('2018-01-02', $employees[1]['orders'][0]['date_created']);
+    }
+
+    public function testFindOneWithManyByJoin()
+    {
+        $employee = $this->getWithManyByJoinMapping()->eq('id', 1)->findOne();
+
+        $this->assertNotNull($employee);
+        $this->assertEquals('Alice', $employee['name']);
+        $this->assertCount(1, $employee['orders']);
+        $this->assertEquals('2018-01-01', $employee['orders'][0]['date_created']);
+    }
+
     /**
      * Returns a new mapping for testing.
      *
@@ -599,6 +644,40 @@ public function getMapping()
         ]);
     }
 
+    /**
+     * Returns a mapping using withOneByJoin for testing.
+     *
+     * @return Mapping
+     */
+    public function getWithOneByJoinMapping()
+    {
+        $employee = (new Definition('employees'))
+            ->withColumns('id', 'name');
+
+        $order = (new Definition('orders'))
+            ->withColumns('id', 'date_created')
+            ->withOneByJoin($employee, 'employee', 'id', 'id', 'orders_fulfillments', 'employee_id', 'order_id');
+
+        return new Mapping($this->db, $order);
+    }
+
+    /**
+     * Returns a mapping using withManyByJoin for testing.
+     *
+     * @return Mapping
+     */
+    public function getWithManyByJoinMapping()
+    {
+        $order = (new Definition('orders'))
+            ->withColumns('id', 'date_created');
+
+        $employee = (new Definition('employees'))
+            ->withColumns('id', 'name')
+            ->withManyByJoin($order, 'orders', 'id', 'id', 'orders_fulfillments', 'order_id', 'employee_id');
+
+        return new Mapping($this->db, $employee);
+    }
+
     /**
      * Returns a new mapping for testing.
      *