如何从其他表中选择字段

Question

i want to select a field from another table, how i can do it in laravel, im still newby in laravel.

here my code

$company = Company::select(
['companies.id', 'companies.CompanyName', 'companies.Discount', 'companies.OrgNumber', 'companies.ExternalID', 'companies.DCity'])
 ->join('companystructures AS cs', 'cs.ChildCompanyID', '=', 'companies.id')
 ->where(['companies.Active' => 1, 'cs.Active' => 1])->get();

i want to add more select to field ParentCompanyID from table companystructures .

i try like this but got error

$company = Company::select(['companies.id', 'companies.CompanyName', 'companies.Discount', 'companies.OrgNumber','companies.ExternalID', 'companies.DCity', '**companystructures.ParentCompanyID**'])
 ->join('companystructures AS cs', 'cs.ChildCompanyID', '=', 'companies.id')
 ->where(['companies.Active' => 1, 'cs.Active' => 1])->get();

Answer 1

Remove ** and use cs.ParentCompanyID instead of companystructures.ParentCompanyID in select

$company = Company::select([
                 'companies.id', 
                 'companies.CompanyName', 
                 'companies.Discount', 
                 'companies.OrgNumber',
                 'companies.ExternalID', 
                 'companies.DCity', 
                 'cs.ParentCompanyID'
             ])
          ->join('companystructures AS cs', 'cs.ChildCompanyID', '=', 'companies.id')
          ->where(['companies.Active' => 1, 'cs.Active' => 1])
          ->get();

Answer 2

You shouldn't do it like this. There is an elegant way to do this using Eloquent Relationships on your Model

First we will define a hasMany relationship in the Company Model like this.

public function structures()
{
  return $this->hasMany(CompanyStructures::class, foreign_key, local_key);
}

Now when we try to query the "Company" model. We can do it like this

return Company::with('structures')->get([ALL_YOUR_SELECT_COLUMNS]);

This will return all the columns defined in the ->get() with all the columns matching in the structures table with primary key of "Company" model.

You can restrict the data with adding a closure to the ->with() pipe and get only the columns that you need. For example if I want to get only the "company structures location" property(I am assuming you would be having one), then we would do something like this.

return Company::with(['structures' => function(){
    return $query->select(columns_from_child_table);
}])->get([ALL_YOUR_SELECT_COLUMNS]);

I hope that solves your answer. I seriously suggest you read the documentation from the link I provided above and make sure you use laravel eloquent as much as possible. Refer the document version according to your laravel version.