Many to many relationship returns empty set - laravel

Question

I have a following table structure in my existing database :
tbl_Grzyby (ID, Nazwa, ...) - main table,
tblk_TypGrzyba (ID, TypGrzyba, OrderNo) - lookup table,
tblm_TypGrzyba (ID_Grzyb, ID_TypGrzyba) (many-to-many table).
I've created a grzyby Eloquent model class, which has a custom property, defined as:
class grzyby extends Model
{
protected $table = 'tbl_Grzyby';
public function typ_grzyba() {
return $this->belongsToMany('\App\Lookups\typ_grzyba', 'tblm_TypGrzyba','ID_Grzyb', 'ID_TypGrzyba');
}
}
I've also created the lookup table model, defined as:
class typ_grzyba extends Model {
protected $table = 'tblk_TypGrzyba';
public function grzyby() {
return $this->belongsToMany('\App\grzyby', 'tblm_TypGrzyba','ID_Grzyb', 'ID_TypGrzyba');
}
}
When I try with tinker to get record from main with ID=67, like:
$main_record=\App\grzyby::where('ID',67)->first();
it returns me all the details for that record fine. Returning all lookups runs also fine:
$types = \App\Lookups\typ_grzyba::all();
However, if I try to do the following:
$main_record_types = $main_record->typ_grzyba;
tinker returns me an empty collection, despite record existing in the many to many table:
When I run the query log it outputs me following SQL query:
select `tblk_TypGrzyba`.*, `tblm_TypGrzyba`.`ID_Grzyb` as `pivot_ID_Grzyb`, `tblm_TypGrzyba`.`ID_TypGrzyba` as `pivot_ID_TypGrzyba` from `tblk_TypGrzyba` inner join `tblm_TypGrzyba` on `tblk_TypGrzyba`.`id` = `tblm_TypGrzyba`.`ID_TypGrzyba` where `tblm_TypGrzyba`.`ID_Grzyb` is null
If I run that query against the database it returns me empty result, however, if I change the where clause manually to
where `tblm_TypGrzyba`.`ID_Grzyb` = 67
I'm getting the expected results in phpMyAdmin.
What's the reason of it and how I can fix that?

Answer 1

The solution was to add the primaryKey overrride because I was using uppercase for the ID field and then restart tinker.

Answer 2

You mixed up your foreign key defintion in your relationships. You wrote this twice:
return $this->belongsToMany('\App\grzyby', 'tblm_TypGrzyba','ID_Grzyb', 'ID_TypGrzyba');
I assume copy pasting? in the second model, justt swap the foreign key. Foreign key of the current model comes first.
In typ_grzyba model, do
public function grzyby() {
return $this->belongsToMany('\App\grzyby', 'tblm_TypGrzyba', 'ID_TypGrzyba', 'ID_Grzyb');
}