Allow custom self column in join

The current `JoinQuery::addJoin()` method does not allow for a
custom `Column`. Below is an example of the use case for this
change:

```php
$query = new Select();

$query
  ->setTable('company')
  ->setColumns([
    'company_id' => 'id',
    'name' => 'name',
  ])
  ->join(
    'field_company_code',
    'id',
    'entity_id',
  )
  ->join(
    'company_codes',
    new Column('target_id', 'field_company_code'),
    new Column('id', 'company_codes'),
    ['code' => 'code']
  );
```

This query structure is common in Drupal when selecting values from
fields on entities that reference other entities through the Field
and Entity API.

src/Manipulation/JoinQuery.php

@@ -10,8 +10,9 @@
 
 namespace NilPortugues\Sql\QueryBuilder\Manipulation;
 
-use NilPortugues\Sql\QueryBuilder\Syntax\SyntaxFactory;
 use NilPortugues\Sql\QueryBuilder\Syntax\Where;
+use NilPortugues\Sql\QueryBuilder\Syntax\Column;
+use NilPortugues\Sql\QueryBuilder\Syntax\SyntaxFactory;
 
 /**
  * Class JoinQuery.
@@ -70,8 +71,8 @@ public function setTable($table)
 
     /**
      * @param string   $table
-     * @param string   $selfColumn
-     * @param string   $refColumn
+     * @param mixed    $selfColumn
+     * @param mixed    $refColumn
      * @param string[] $columns
      *
      * @return Select
@@ -83,8 +84,8 @@ public function leftJoin($table, $selfColumn = null, $refColumn = null, $columns
 
     /**
      * @param string   $table
-     * @param string   $selfColumn
-     * @param string   $refColumn
+     * @param mixed    $selfColumn
+     * @param mixed    $refColumn
      * @param string[] $columns
      * @param string   $joinType
      *
@@ -110,8 +111,8 @@ public function join(
 
     /**
      * @param Select $select
-     * @param string $selfColumn
-     * @param string $refColumn
+     * @param mixed  $selfColumn
+     * @param mixed  $refColumn
      *
      * @return Select
      */
@@ -121,11 +122,15 @@ public function addJoin(Select $select, $selfColumn, $refColumn)
         $table = $select->getTable()->getName();
 
         if (!isset($this->joins[$table])) {
-            $newColumn = array($selfColumn);
-            $select->joinCondition()->equals(
-                $refColumn,
-                SyntaxFactory::createColumn($newColumn, $this->select->getTable())
-            );
+            if (!$selfColumn instanceof Column) {
+                $newColumn = array($selfColumn);
+                $selfColumn = SyntaxFactory::createColumn(
+                    $newColumn,
+                    $this->select->getTable()
+                );
+            }
+
+            $select->joinCondition()->equals($refColumn, $selfColumn);
             $this->joins[$table] = $select;
         }
 
@@ -148,8 +153,8 @@ public function setJoin($isJoin = true)
 
     /**
      * @param string   $table
-     * @param string   $selfColumn
-     * @param string   $refColumn
+     * @param mixed    $selfColumn
+     * @param mixed    $refColumn
      * @param string[] $columns
      *
      * @internal param null $selectClass
@@ -163,8 +168,8 @@ public function rightJoin($table, $selfColumn = null, $refColumn = null, $column
 
     /**
      * @param string   $table
-     * @param string   $selfColumn
-     * @param string   $refColumn
+     * @param mixed    $selfColumn
+     * @param mixed    $refColumn
      * @param string[] $columns
      *
      * @return Select
@@ -176,8 +181,8 @@ public function crossJoin($table, $selfColumn = null, $refColumn = null, $column
 
     /**
      * @param string   $table
-     * @param string   $selfColumn
-     * @param string   $refColumn
+     * @param mixed    $selfColumn
+     * @param mixed    $refColumn
      * @param string[] $columns
      *
      * @return Select

tests/Builder/Syntax/SelectWriterTest.php

@@ -10,9 +10,10 @@
 
 namespace NilPortugues\Tests\Sql\QueryBuilder\Builder\Syntax;
 
-use NilPortugues\Sql\QueryBuilder\Builder\GenericBuilder;
-use NilPortugues\Sql\QueryBuilder\Manipulation\Select;
+use NilPortugues\Sql\QueryBuilder\Syntax\Column;
 use NilPortugues\Sql\QueryBuilder\Syntax\OrderBy;
+use NilPortugues\Sql\QueryBuilder\Manipulation\Select;
+use NilPortugues\Sql\QueryBuilder\Builder\GenericBuilder;
 
 /**
  * Class SelectWriterTest.
@@ -356,6 +357,33 @@ public function itShouldBeAbleToDoAJoinWithOrderByOnJoinedTable()
         $this->assertSame($expected, $this->writer->write($this->query));
     }
 
+    /**
+     * @test
+     */
+    public function itShouldBeAbleToDoAJoinWithCustomColumns()
+    {
+        $this->query
+            ->setTable('user')
+            ->setColumns(
+                array(
+                    'userId' => 'user_id',
+                    'username' => 'name',
+                    'email' => 'email',
+                    'created_at',
+                )
+            )
+            ->orderBy('user_id', OrderBy::DESC)
+            ->join('news', 'user_id', 'author_id', array('title', 'body', 'created_at', 'updated_at'))
+            ->orderBy('created_at', OrderBy::DESC)
+            ->join('articles', new Column('news_id', 'article'), new Column('id', 'news'));
+
+        $expected = 'SELECT user.user_id AS "userId", user.name AS "username", user.email AS "email", user.created_at,'.
+            ' news.title, news.body, news.created_at, news.updated_at FROM user JOIN news ON (news.author_id ='.
+            ' user.user_id) JOIN articles ON (news.id = article.news_id) ORDER BY user.user_id DESC, news.created_at DESC';
+
+        $this->assertSame($expected, $this->writer->write($this->query));
+    }
+
     /**
      * @test
      */