如何在 Laravel 中正确使用 with() 关系？

Question

I just wanted to clarify using the relationship in tables. Right now, I wanted to fetch records of designation names from designation_id in employees table.

 <?php namespace App\Models; use Illuminate\Database\Eloquent\Factories\HasFactory; use Illuminate\Database\Eloquent\Model; use App\Models\{ Designations, Positions }; class Employees extends Model { use HasFactory; protected $table = 'employees'; protected $primaryKey = 'id'; public $timestamps = true; protected $casts = [ 'designation_id' => 'array', 'position_id' => 'array', 'basic_pay' => 'decimal:2', ]; protected $dates = ['created_at', 'updated_at']; protected $fillable = [ 'first_name', 'last_name', 'designation_id', 'position_id', 'basic_pay', ]; public function designations() { return $this->hasMany(Designations::class, 'id', 'designation_id'); } public function positions() { return $this->hasMany(Positions::class, 'id', 'position_id'); } }

Here's my designation model:

 <?php namespace App\Models; use Illuminate\Database\Eloquent\Factories\HasFactory; use Illuminate\Database\Eloquent\Model; use App\Models\Employees; class Designations extends Model { use HasFactory; protected $table = 'designations'; protected $primaryKey = 'id'; public $timestamps = true; protected $dates = ['created_at', 'updated_at']; protected $fillable = [ 'name', 'description' ]; public function employees() { return $this->belongsTo(Employees::class, 'designation_id'); } }

Here's my EmployeeController.php :

 <?php namespace App\Http\Controllers; use Illuminate\Http\Request; use App\Models\{ Employees, Designations }; class EmployeesController extends Controller { public function index() { $employees = Employees::with('designations', 'positions')->get(); return array_reverse($employees); } }

I checked my api url, http://localhost:8000/api/employees and got this error:

SQLSTATE[HY093]: Invalid parameter number (SQL: select * from designations where designations . id in (52))

Answer 1

Your relationships parameters are wrong. It's

hasMany(class, foreignKey, relatedPrimaryKey)

# Employee
public function designations()
{
    return $this->hasMany(Designations::class, 'employee_id', 'id');
}

public function positions()
{
    return $this->hasMany(Positions::class, 'employee_id', 'id');
}

If you're eager loading more than 1 relationship, use array notation.

Also, $employees will be an instance of a Collection , so you can't use it as an argument to array_reverse .

You can either use collection methods to achieve the same result, or use $employees->all() to get the underlying array.

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use App\Models\Employees;

class EmployeesController extends Controller
{
    public function index()
    { 
        $employees = Employees::with(['designations', 'positions'])->get();

        return $employees->reverse()->values()->all();
        // OR
        return array_reverse($employees->all());
    }
}

---

This is assuming your tables have a structure like this:

Schema::create('employees', function (Blueprint $table) {
    $table->id();
    ...    
});

Schema::create('designations', function (Blueprint $table) {
    $table->id();
    $table->foreignId('employee_id')->constained('employees');
    ...
});

Schema::create('positions', function (Blueprint $table){
    $table->id();
    $table->foreignId('employee_id')->constained('employees');
    ...
});

Since you're using increments instead of id() , the code has to be a little different.

Schema::create('employees', function (Blueprint $table) {
    $table->increments('id')->unique();
    ...    
});

Schema::create('designations', function (Blueprint $table) {
    $table->increments('id')->unique();
    $table->unsignedInteger('employee_id');
    $table->foreign('employee_id')->references('id')->on('employees');
    ...
});

Schema::create('positions', function (Blueprint $table){
    $table->increments('id')->unique();
    $table->unsignedInteger('employee_id');
    $table->foreign('employee_id')->references('id')->on('employees');
    ...
});

Answer 2

I would recommend you to install phpstorm, it gives you hints of function parameters and you won't have this kind of issues anymore.

correct format is:

 return $this->hasMany('App\Comment', 'foreign_key', 'local_key');

in your designations model:

 public function DesignationNames() { return $this->hasMany(\App\Models\Employees::class, 'designation_id', 'id'); }

When you retrieve them in your controller you need to use the with() method as:

Designations::with('DesignationNames')->get();

And then to access properties in the related employee collection you would need to:

$designation->DesignationNames->DesignationProperty