$many_many relation in summary fields

Question

I have two classes with a $many_many and $belongs_many_many relation between them. I tried to define $summary_fields in the class that contains the $many_many to display the relation between the classes but that column ('Column2.Column2') displays blank results. How do I set $summary_fields to display this data correctly?

Here is my code

class Table1 extends DataObject {

    private static $db = array(
        'Column1' => 'Varchar(32)'
    );

    private static $many_many = array (
        'Column2' => 'Table2'
    );

    private static $summary_fields = array (
        'Column1' => 'Column 1',
        'Column2.Column2' => 'Column 2'
    );
}

class Table2 extends DataObject {

    private static $db = array(
        'Column2' => 'Varchar(32)'
    );

    private static $belongs_many_many = array (
        'Column1' => 'Table1'
    );
}

Answer 1

The issue is a $many_many relationship or a $has_many relationship can be linked to multiple objects. We cannot put a $many_many or $has_many into $summary_fields as a single row as the GridField does not know how to display more than one item.

For example, say we have Columns.Title where Columns is a $many_many relationship on the current object. If we have three Columns objects linked to the current object, the system doesn't know to display the Title of the three columns.

What we can do is create a function to return a string displaying the data that we want to display.

The following code is written for Silverstripe 3.

class Table1 extends DataObject
{
    private static $db = [
        'Title' => 'Varchar(32)',
    ];

    private static $many_many = [
        'Columns' => 'Table2',
    ];

    private static $field_labels = [
        'ColumnsString' => 'Columns',
    ];

    private static $summary_fields = [
        'Title',
        'ColumnsString',
    ];

    public function ColumnsString()
    {
        return implode(', ', $this->Columns()->column('Title'));
    }
}

class Table2 extends DataObject
{
    private static $db = [
        'Title' => 'Varchar(32)',
    ];

    private static $belongs_many_many = [
        'Columns' => 'Table1',
    ];
}