Silverstripe: Filtering a $DataObject::get()

I'm building an archive page and I'm having trouble pulling and filtering my results by year.

The page type has a dropdown to select which year should be displayed

private static $db = array(
    "SubType" => "Enum(array('2013', '2014', '2015', '2016', '2017', '2018'))"
);

The template calls a function GetFilms

public function GetFilms()
{
    $films = DataObject::get("Film");
    return $films;
}

If I use the function above it works but displays all the films.

When I try to modify it to filter using the year its been passed,

public function GetFilms($SubType)
{
    $films = DataObject::get("Film","'Year' = '$SubType'");
    return $films;
}

The page no longer displays any of the films. Does anyone know what I'm doing wrong?

Here's the code for displaying the results,

<% loop GetFilms($SubType) %>
    <div class="film" data-title="$Title">
        <a href="$Top.Link?film=$ID">
        <div class="inner">
            <h3 class="filmTitle">$Title</h3>
            <img class="filmImg" src="$FilmImage.URL" alt="$Title" />
        </div>
        </a>
    </div>
<% end_loop %>

Thank you for your help!

Solution

What I'd suggest is doing some debugging. You can add some points into GetFilms() e.g. var_dump($SubType); to see what the template is passing in. You should check that your Film DataObjects can be accessed manually by using dummy values, e.g. Film::get()->filter(['Year' => 2013]), then once you've eliminated the data source and the method's input as problem areas you can piece it back together.

I'd also suggest moving away from DataObject::get arguments to a chainable approach using DataList methods, e.g.:

public function GetFilms($SubType)
{
    return Film::get()->filter(['Year' => $SubType]);
}