Hi Everyone,

Long time stalker, first time poster. I'm still a SilverStripe noob so please be gentle. I'm working with a Course class and a page that has_many Courses. Defined below:

<?php
	class Course extends DataObject {
		static $db = array(
			"Name" => "Varchar",
			"Number" => "Int",
			"Description" => "Text",
			"Active" => "Boolean"
		);
		
		static $has_one = array(
			"Category" => "CourseCategory"
		);
		
		public function getCMSFields_forPopup()
		{
			$categories = DataObject::get("CourseCategory");
			$dropdown = new DropdownField('Category');
			
			if ($categories) {
				$map = $categories->toDropDownMap('ID', 'Name');	
				$dropdown = new DropdownField('CategoryID', 'Category', $map);
			}
			
			return new FieldSet(
				$dropdown,
				new TextField('Name'),
				new TextField('Number'),
				new TextareaField('Description'),
				new CheckboxField('Active')
			);
		}
	}




<?php
class CoursesPage extends StandardPage {

	static $has_many = array(
		"Courses" => "Course"
	);

	public function getCMSFields() {
		$fields = parent::getCMSFields();
		
		$course_fields = new DataObjectManager(
			$this,
			"Courses",
			"Course",
			array("Category.Name" => "Category", "Number" => "Number","Name" => "Name", "Description" => "Description", "Active" => "Active"),
			"getCMSFields_forPopup"
		);
		
		$course_category_fields = new DataObjectManager(
			$this,
			"Categories",
			"CourseCategory",
			array("Name" => "Name"),
			"getCMSFields_forPopup"
		);

		$fields->addFieldToTab("Root.Content.Courses", $course_fields);
		$fields->addFieldToTab("Root.Content.Categories", $course_category_fields);
		
		return $fields;
	}

}

class CoursesPage_Controller extends StandardPage_Controller {

	public function init() {
		parent::init();
		Requirements::themedCSS('courses');
	}
	
}
?>

The front-end errors out with the following when I try to call Courses:

Error at sapphire/core/model/MySQLDatabase.php line 525: Couldn't run query: 
SELECT "Course"."ClassName", "Course"."Created", "Course"."LastEdited", "Course"."Name", "Course"."Number", "Course"."Description", "Course"."Active", "Course"."CategoryID", "Course"."ID", CASE WHEN "Course"."ClassName" IS NOT NULL THEN "Course"."ClassName" ELSE 'Course' END AS "RecordClassName"
FROM "Course"
WHERE ("ParentID" = '11') 

Unknown column 'ParentID' in 'where clause' ({SITE_URL}/courses)

At one point I actually dropped Course and CourseCategory from the Database because they were giving me so many problems. Now I feel like that missing field is a product of myself messing with the database. I'm hoping there's an easy solution to this or I've overlooked something.

Many thanks!

Figured it out. I missed the fact that a $has_many relationship requires a $has_one on the related class.