Laravel belongsTo returning null when using 'with' - php

Question

I'm just getting started with Laravel so please forgive any noobness.
I have a User and Order model, a user has many orders:
# Inside User model
public function orders()
{
$this->hasMany('Order');
}
# Inside Order
public function user()
{
return $this->belongsTo('User');
}
// Not sure if this is upsetting anything (also in Order)
public function products()
{
return $this->belongsToMany('Product');
}
So I think I have the above right.
But when I do this:
$users = User::with('orders')->find(1);
return $users;
I get Call to a member function addEagerConstraints() on null.
However, if I do it the other way around, it works great:
$orders = Order::with('User')->get();
return $orders;
What am I doing wrong / what don't I understand?! Or is my problem bigger than I think?
Database:

Answer 1

The problem is you don't have return for your orders relationship. It should be:
public function orders(){
return $this->hasMany('Order');
}
You should also use your relationships case sensitive. you showed:
$orders = Order::with('User')->get();
is working, but you should rather use
$orders = Order::with('user')->get();
to avoid extra queries to your database in future

Answer 2

For anyone else that runs across this, I was having the same issue, but my problem was that I had the foreign/local keys swapped. Example:
// This is correct for hasX relationships
public function user() {
return $this->hasOne('App\Models\User', 'user_id', 'local_key_user_id');
}
// This is correct for belongsTo relationships
public function user() {
return $this->belongsTo('App\Models\User', 'local_key_user_id', 'user_id');
}
Notice that for hasX relationships, the foreign key is the second parameter, and the local key is the third. However, for belongsTo relationships, these two are swapped.

Answer 3

Probably doesn't answer this particular question but it relates to the title. I had the same issue here is the wrong query
$offer = Offer::with([
'images:name,id,offer_id',
'offer_options:offer_option,value,id,offer_id',
'user:id,name,avatar'])
->select(['id', 'views', 'type', 'status'])
->where('id', $id)->get();
the model look like this
class Offer extends Model {
function user(): BelongsTo {
return $this->belongsTo(User::class);
}
}
The User
class User extends ..... {
function offer(): HasMany {
return $this->hasMany(Offer::class);
}
}
The issue with the query is I was not selecting user_id, i.e in my select function user_id column was not included and that is why I was getting null for user
according to Laravel docs
When using this feature, you should always include the id column and
any relevant foreign key columns in the list of columns you wish to
retrieve.
So the correct query is
$offer = Offer::with([
'images:name,id,offer_id',
'offer_options:offer_option,value,id,offer_id',
'user:id,name,avatar'])
->select(['id', 'views', 'type', 'status','user_id'])
->where('id', $id)->get();