从实体关系获取唯一的ID，而不会在Doctrine中获取整个对象 [英] Getting only ID from entity relations without fetching whole object in Doctrine

问题描述

假设我有一个实体，它引用自身来映射父子关系

  class Food 
 {
 / ** 
 * @ ORM\Id 
 * @ ORM\Column（type =integer）
 * @ ORM\GeneratedValue（strategy =AUTO ）
 * / 
 protected $ id; 
 
 / ** 
 * @ ORM\ManyToOne（targetEntity =Food，inversedBy =foodChildren）
 * @ ORM\JoinColumn（name =food_group_id ，nullable = true）
 * / 
 protected $ foodGroup; 
 
 / ** 
 * @ ORM\OneToMany（targetEntity =Food，mappedBy =foodGroup，fetch =LAZY，cascade = {remove}）
 * / 
 protected $ foodChildren; 
  

我有一个用例，我想要得到 food_group_id ，而不会从数据库中获取完整的父对象。使用 fetch =LAZY不会让Doctrine再次查询。有没有办法只在获得 $ food-> getFoodGroup（）时返回ID？

解决方案

不要使你的生活复杂化，你可以做

  $ food-> getFoodGroup ） - > getId（）
  

此不会执行任何其他查询或触发懒惰加载！

为什么？因为您的 $ food-> foodGroup 是一个知道它的ID的代理对象。如果您调用某个尚未加载的字段的getter方法，则只会执行延迟加载。

Assume I've an entity, which references itself to map parent-child-relations

class Food
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

    /**
     * @ORM\ManyToOne(targetEntity="Food", inversedBy="foodChildren")
     * @ORM\JoinColumn(name="food_group_id", nullable=true)
     */
    protected $foodGroup;

    /**
     * @ORM\OneToMany(targetEntity="Food", mappedBy="foodGroup", fetch="LAZY", cascade={"remove"})
     */
    protected $foodChildren;

I have a use case where I want to get food_group_id of an entity without getting full parent object from database. Using fetch="LAZY" doesn't keep Doctrine from querying again. Is there a way to return only the ID when getting $food->getFoodGroup()?

解决方案

Don't complicate your life, you can just do

$food->getFoodGroup()->getId()

This WILL NOT perform any additional query or trigger lazy load!

Why? Because your $food->foodGroup is a proxy object which knows about it's ID. It will only do lazy load if you call a getter method of some field which hasn't been loaded.

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