我创建了一个包含产品和类别的数据库:

I have created a database with products and categories:

CREATE TABLE categoria(
id       int(255) auto_increment not null,
nombre     varchar(50),
CONSTRAINT pk_categoria PRIMARY KEY(id),
)ENGINE = InnoDb;

CREATE TABLE producto(
id       int(255) auto_increment not null,
nombre     varchar(50),
categoria int(11),
createdAt datetime,
updatedAt datetime,
CONSTRAINT pk_producto PRIMARY KEY(id),
CONSTRAINT fk_producto_categoria FOREIGN KEY(categoria) references categoria(id),
)ENGINE = InnoDb;

当使用 twig 打印产品时，它会显示除类别编号之外的所有字段，我收到错误消息:

When printing with twig the product, and it shows all the fields, except the one of the category number, that I get the error:

在渲染模板期间引发了异常(Catchable >Fatal Error: Object of class Proxies__CG__BackendBundleEntityCategoria >无法转换为字符串").

An exception has been thrown during the rendering of a template ("Catchable >Fatal Error: Object of class Proxies__CG__BackendBundleEntityCategoria >could not be converted to string").

有解决这个问题的办法吗?

Any idea to solved this issue?

BackendBundleEntityProducto:
    type: entity
    table: producto
    indexes:
        fk_producto_categoria:
            columns:
                - categoria
    id:
        id:
            type: integer
            nullable: false
            options:
                unsigned: false
            id: true
            generator:
                strategy: IDENTITY
    fields:
        nombre:
            type: string
            nullable: true
            length: 100
            options:
                fixed: false
        createdat:
            type: datetime
            nullable: true
            column: createdAt
        updatedat:
            type: datetime
            nullable: true
            column: updatedAt
    manyToOne:
        categoria:
            targetEntity: Categoria
            cascade: {  }
            fetch: LAZY
            mappedBy: null
            inversedBy: null
            joinColumns:
                categoria:
                    referencedColumnName: id
            orphanRemoval: false
    lifecycleCallbacks: {  }

categoria.orm.yml

BackendBundleEntityCategoria:
    type: entity
    table: categoria
    id:
        id:
            type: integer
            nullable: false
            options:
                unsigned: false
            id: true
            generator:
                strategy: IDENTITY
    fields:
        nombre:
            type: string
            nullable: true
            length: 50
            options:
                fixed: false
    lifecycleCallbacks: {  }

producto.php

<?php

namespace BackendBundleEntity;
use SymfonyComponentSecurityCoreUserUserInterface;

/**
 * Producto
 */
class Producto
{
    /**
     * @var integer
     */
    private $id;

    /**
     * @var string
     */
    private $nombre;

   /**
     * @var integer
     */
    private $categoria;

    /**
     * @var DateTime
     */
    private $createdAt;

    /**
     * @var DateTime
     */
    private $updatedAt;


    /**
     * Get id
     *
     * @return integer
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set nombre
     *
     * @param string $nombre
     *
     * @return Producto
     */
    public function setNombre($nombre)
    {
        $this->nombre = $nombre;

        return $this;
    }

    /**
     * Get nombre
     *
     * @return string
     */
    public function getNombre()
    {
        return $this->nombre;
    }

    /**
     * Set categoria
     *
     * @param integer $categoria
     *
     * @return Producto
     */
    public function setCategoria($categoria)
    {
        $this->categoria = $categoria;

        return $this;
    }

    /**
     * Get categoria
     *
     * @return integer
     */
    public function getCategoria()
    {
        return $this->categoria;
    }

    /**
     * 
     */
    public function __toString(){

        return $this->id;
    }

    /**
     * Set createdAt
     *
     * @param DateTime $createdAt
     *
     * @return Producto
     */
    public function setCreatedAt($createdAt)
    {
        $this->createdAt = $createdAt;

        return $this;
    }

    /**
     * Get createdAt
     *
     * @return DateTime
     */
    public function getCreatedAt()
    {
        return $this->createdAt;
    }

    /**
     * Set updatedAt
     *
     * @param DateTime $updatedAt
     *
     * @return Producto
     */
    public function setUpdatedAt($updatedAt)
    {
        $this->updatedAt = $updatedAt;

        return $this;
    }

    /**
     * Get updatedAt
     *
     * @return DateTime
     */
    public function getUpdatedAt()
    {
        return $this->updatedAt;
    }   

    /**
     * @var DateTime
     */
    private $createdat;

    /**
     * @var DateTime
     */
    private $updatedat;

}

推荐答案

你正试图通过 Twig 回显"一个对象.在这种情况下，类别"对象.您可能不想回显对象，而是想回显名称，例如；

You are trying to "echo" an object through Twig. In this case the "Categoria" object. Instead of echoing the object, you problably want to echo the name like;

{{ producto.categoria.nombre }} 

解决此问题的另一种方法是向 Categoria 实体添加一个 __toString 方法，例如 ;

Another way to solve this problem is adding a __toString method to the Categoria entity like ;

class Categoria
{
    ...

    /**
     * @var string
     */
    private $nombre;

    ...

    public function __toString()
    {
        return $this->nombre; 
    }
}

你在这里所做的就是告诉 PHP，无论何时你以字符串的形式访问对象Categoria"，你都应该使用它的名字.因此，当您尝试 echo $categoria 或 {{ categoria }} 时，PHP 将查找 __toString 方法并回显您在该方法中返回的任何内容.

What you do here is tell PHP that whenever you access the object "Categoria" as a string, you should use its name. So when you try echo $categoria or {{ categoria }} PHP will look for the __toString method and echo whatever you return in that method.

尽管我仍然更喜欢你明确地使用 {{ categoria.name }} ！

Allthough I still prefer you explicitly use {{ categoria.name }} !