SQLSTATE[42S22]: Column not found: 1054 Unknown column 'cid' in 'where clause' (SQL: select * from `category` where `cid` is null)

In Category Schema, there is no column named as 'cid'.

Schema should be like:

Schema::create('category', function (Blueprint $table) {
        $table->increments('ctid');
        $table->integer('cid');
        $table->string('name');
        $table->timestamps();
    });

You don't have cid field on category table. Did you meant ctid?

$categories = category::where('ctid', $cid)->with('Contract')->get();

or

$categories = category::whereHas('Contract', function ($query) use ($cid) {
    $query->where('cid', $cid);
})->get();

@Yorki I tried the first solution see the error i got

(E_RECOVERABLE_ERROR) Argument 2 passed to with() must be callable or null, object given, called in C:\xampp\htdocs\project\app\Http\Controllers\HomeController.php on line 107

Looks to me like you've swapped cid and ctid around in your definitions. This is why you should avoid abbreviating your column names.

@Yorki I tried the second solution and i am still getting errors

Symfony \ Component \ Debug \ Exception \ FatalThrowableError (E_ERROR) Call to a member function getRelationExistenceQuery() on null

Post your models, specifically, the relationships you've defined in them.

You have messed up models. Try with lowercase in whereHas('contract'). You should name you models with camel case.

The error is maybe in your Controller code:

$cid = $contracts->id; 

//should be 

$cid = $contracts->cid;

Maybe the setup for the pivot-table is not working correct, it should be singular and in alphabetical order category_contract to work out of the box

The SQL Error will result from the wrong call

$categories = category::where('cid', $cid)->with('Contract')->get();

because 'cid' is no field of the category table

@36864 these are the models

Ignoring the capitalization issues for now, you've simply defined your relationships wrong. You're not even returning anything from the Contract relationship in your category class.

What you have here is a many-to-many relationship between category and contract. This should be defined like this:

//category model
public function contract() 
{
    return $this->belongsToMany(Contract::class, 'contract_categories');
}

//contract model
public function category()
{
    return $this->belongsToMany(Category::class, 'contract_categories');
}

This is the crap

$categories = category::where('cid', $cid)->with('Contract')->get();

1. schema should be

      Schema::create('categories', function (Blueprint $table) {
          $table->increments('id');
          $table->string('name');
          $table->timestamps();
      });
   
   Schema::create('contracts', function (Blueprint $table) {
          $table->increments('id');
          $table->string('number');
          $table->timestamps();
      });
   
      Schema::create('category_contract', function (Blueprint $table) {
          $table->unsignedInteger('category_id');
          $table->unsignedInteger('contract_id');
      });
   
   

2. The Model setup

   class Category extends Model
   {
       public function contract() {
           return $this->belongsToMany(Contract::class);
       }
   }
   
   class Contract extends Model
   {
       public function category() {
           return $this->belongsToMany(Category::class);
       }
   }
   

3. Controller code

   // get contract with id=1 with all categories
   $contract = App\Contract::with('category')->where('id', 1)->first();
   
   // or get all contracts by category with id=1 
   $category = App\Category::with('contract')->where('id', 1)->first();
   
   // get all categories
   $categories = App\Category::all();
   
   return view('contractTable')
      ->with([
      'categories' => $categories,
      'contract' => $contract
      ]);
   
   

4. View code

 ```php
 <h3>all categories</h3>
 @foreach($categories as $category)
     <ul>
         <li>{{ $category->name }}</li>
         </ul>
 @endforeach 

 <h3>contract number</h3>
 {{ $contract->number }}

 ```

or you fetch all contracts with categories and filter the collection by id without querying the database again

$contracts = App\Contract::with('category')->get();
$contract1 = $contracts->firstWhere('id', 1);
//...
$contract9 = $contracts->firstWhere('id', 9); 

//or a subset

$some_contracts = $contracts->where('id', '>', 1); 

@pantox thannks for your suggestion, but if i alter my schema, the rest of the project will fall apart, also this is my models

contract_category model ...

like @36864 suggested, you have to be explicit in your definition of the manyToMany relationship

with your schema you have to define your models (Category and Contract) like this

class Category extends Model
{
    public function contract() {
        return $this->belongsToMany(Contract::class, 'contract_categories', 'ctid' , 'cid');
    }
}

class Contract extends Model
{
    public function category() {
        return $this->belongsToMany(Category::class, 'contract_categories', 'cid', 'ctid');
    }
}