Eloquent BelongsToMany Relationship searches for is null - php

Question

I have 3 tables artist, catalog & cat_artist (pivot table). When retrieving a row from my catalog table I want to get all the associated artists with it. I could just do this with raw sql but since using laravel it feels wrong because it has many of the functions to do this already. So I have a the function in my product model (product modal references the catalog table) to create the join
public function artists()
{
return $this->belongsToMany('App\Artist', 'cat_artist', 'LOOK_UP_TO_CAT_ID', 'LOOK_UP_TO_ARTIST_ID');
}
I then call this before I return my view which gives me the the row from my catalog table
$product = Product::find($id);
Now I want to get all the artists that may belong to this product aswell so I call the following
$artists = $product->artists()->get();
This returns an emtpy result set
Here is the query log from the above
array(2) {
[0]=> array(3) {
["query"]=> string(60) "select * from `catelogue` where `catelogue`.`id` = ? limit 1"
["bindings"]=> array(1) {
[0]=> int(96033)
}
["time"]=> float(0.91)
}
[1]=> array(3) {
["query"]=> string(289) "select `artist`.*, `cat_artist`.`LOOK_UP_TO_CAT_ID` as `pivot_LOOK_UP_TO_CAT_ID`, `cat_artist`.`LOOK_UP_TO_ARTIST_ID` as `pivot_LOOK_UP_TO_ARTIST_ID` from `artist` inner join `cat_artist` on `artist`.`id` = `cat_artist`.`LOOK_UP_TO_ARTIST_ID` where `cat_artist`.`LOOK_UP_TO_CAT_ID` is null"
["bindings"]=> array(0) { }
["time"]=> float(0.37) } }
This is all happening before I return the view and pass the data to the view
Everything else in the query is right apart from this where it's looking for null
where `cat_artist`.`LOOK_UP_TO_CAT_ID` is null
It should be this
where `cat_artist`.`LOOK_UP_TO_CAT_ID` = ?
Please help. I can't figure out where I have gone wrong
EDIT
Here are my DB tables - watered down as showing all cols would be a waste
CREATE TABLE IF NOT EXISTS `artist` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`ARTIST` varchar(255) DEFAULT NULL,
PRIMARY KEY (`ID`),
KEY `ARTIST` (`ARTIST`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ;
CREATE TABLE `catelogue` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`CAT_NO` varchar(255) DEFAULT NULL,
`TITLE` varchar(255) DEFAULT NULL,
`BARCODE` varchar(15) DEFAULT NULL,
PRIMARY KEY (`ID`),
UNIQUE KEY `BARCODE` (`BARCODE`),
UNIQUE KEY `CAT_NO` (`CAT_NO`),
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `cat_artist` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`LOOK_UP_TO_CAT_ID` int(11) NOT NULL,
`LOOK_UP_TO_ARTIST_ID` int(11) NOT NULL DEFAULT '1',
PRIMARY KEY (`ID`),
UNIQUE KEY `unique_index` (`LOOK_UP_TO_CAT_ID`,`LOOK_UP_TO_ARTIST_ID`),
KEY `LOOK_UP_TO_CAT_ID` (`LOOK_UP_TO_CAT_ID`),
KEY `LOOK_UP_TO_ARTIST_ID` (`LOOK_UP_TO_ARTIST_ID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Hopefully an answer can be found as to why it is putting is null in the where statement rather than the product ID
Also I have tested the resulting raw SQl by replacing is null with a product id and it does work in phpMyAdmin so the SQL been generated is correct up to the is null

Answer 1

This may sounds stupid, but I think it's beacuse your field names are in uppercase letters. so laravel cannot find the id column in attributes list in Project model. so it assumes you are search for null ids.
So at least rename ID columns to id(lowercase).

Answer 2

After lots of digging I found that I was using the wrong var to set the $primaryKey. I was using $primary_id. How or where I picked this up I don't know but it seems to be the root cause because I wasn't changing the primaryKey var but rather declaring a new one - Stupid user error
To Any one else finding this - double check your code.
Make sure you are assigning the correct variable.
Wrapping a pre tag around my var_dump helps to read a large obeject/array and helped me to find the issue