CakePHP 4 - for 2 foreign keys in Table A, get corresponding data from Table B

Question

Using CakePHP 4.1.6

I have two tables in my database called Categories and CategoryChanges . The Categories table is simple in that it contains a list with ID's and names of several categories, eg

id | name
------------
1  | Foo
------------
2  | Bar
------------
3  | Baz
------------

My other table, CategoryChanges , is a log of when categories (as in Categories ) in the application have been changed, as well as some other data such as who changed them and when.

In CategoryChanges there are two columns category_id_from and category_id_to which correspond to Categories.id .

So as an example CategoryChanges may include the following:

id | category_id_from | category_id_to | created    | user | notes 
--------------------------------------------------------------------
80 | 2                | 3              | 2021-02-03 | John | abcdef
--------------------------------------------------------------------
81 | 3                | 3              | 2021-03-15 | Jack | ghi
--------------------------------------------------------------------
82 | 1                | 2              | 2021-03-18 | Dave | zzz
--------------------------------------------------------------------

What I'm trying to do is output a table on a webpage which shows the above information but instead of having category_id_from and category_id_to as the numerical ID, I want Categories.name to appear. Note that it is also possible for some rows that the "from" and "to" values are the same (as an example see CategoryChanges.id = 81 ).

So the output I want would be this:

id | category_from | category_to | created    | user | notes 
--------------------------------------------------------------------
80 | Bar           | Baz         | 2021-02-03 | John | abcdef
--------------------------------------------------------------------
81 | Baz           | Baz         | 2021-03-15 | Jack | ghi
--------------------------------------------------------------------
82 | Foo           | Bar         | 2021-03-18 | Dave | zzz
--------------------------------------------------------------------

After reading the Query Builder docs I can't see how to do this.

My assumption is that I need to read from the CategoryChanges table which is straightforward:

// in a Controller method
$CategoryChanges = $this->getTableLocator->get('CategoryChanges');
$query = $CategoryChanges->find();

If I execute $query->toArray() I would get the second table above, which contains the numerical ID's for category_id_from and category_id_to .

I assume that $query needs additional conditions - or possibly virtual fields - for "category from" and "category to". I can't see how to join these two columns to Categories such that I can get Categories.name as per table 3.

Answer 1

You could for example simply add two belongsTo associations for those fields to your CategoryChanges table, and then comfortably use innerJoinWith() with your query, like:

$this
    ->belongsTo('CategoryFrom')
    ->setClassName('Categories')
    ->setForeignKey('category_id_from');
    
$this
    ->belongsTo('CategoryTo')
    ->setClassName('Categories')
    ->setForeignKey('category_id_to');

$query = $CategoryChanges
    ->find()
    ->select([
        'id',
        'category_from' => 'CategoryFrom.name',
        'category_to' => 'CategoryTo.name',
        'created',
        'user',
        'notes',
    ])
    ->innerJoinWith('CategoryFrom')
    ->innerJoinWith('CategoryTo');