当Doctrine不允许我将复合主键与另一个实体的外键关联时，如何为ER图建模？

Question

I am trying to model the ManyToOne relations between

1. product_pricename and category_pricename
2. price_history and product_pricename , as in the diagram below:

How?

Where I'm at

I note that this ER Diagram contains a composite foreign key ,

I am talking about table product_pricename with key of (category_pricename_category_id, category_pricename_pricename_id)

which is part of another entity's primary key

I am talking about category_pricename with PRIMARY KEY of (category_id, pricename_id)

Which is totally okay by MySQL. But when I try to model this in Doctrine I get an error:

[Doctrine\ORM\Mapping\MappingException]
It is not possible to map entity 'CategoryPricename' with a composite 
primary key as part of the primary key of another entity
'ProductPricename#categoryPricename'.

I so far have not visualized a proper way to do this in Doctrine.

I'm thinking I could introduce a surrogate PRIMARY KEY to entities product_pricename and category_pricename and re-model my tables. But would that be a way to do it?

Relevant Code

class CategoryPricename
{

    /**
     * @Id @ManyToOne(targetEntity="Category")
     * @JoinColumn(name="category_id", referencedColumnName="id", nullable=false)
     *
     * @var Category
     */
    private $category;

    /**
     * @Id @ManyToOne(targetEntity="Pricename")
     * @JoinColumn(name="pricename_id", referencedColumnName="id", nullable=false)
     *
     * @var Pricename
     */
    private $pricename;
}

class ProductPricename
{

    /**
     * @Id @ManyToOne(targetEntity="Product")
     * @JoinColumn(name="product_id", referencedColumnName="id", nullable=false)
     *
     * @var Product
     */
    private $product;

    /**
     * Note:  I shortened the column names for my code
     * by removing "category_pricename_" prefix for brevity
     * as reflected in JoinColumn's name attributes
     *
     * @Id
     * @ManyToOne(targetEntity="CategoryPricename")
     * @JoinColumns({
     *   @JoinColumn(name="category_id", referencedColumnName="category_id", nullable=false),
     *   @JoinColumn(name="pricename_id", referencedColumnName="pricename_id", nullable=false)
     * })
     *
     * @var CategoryPricename
     */
    private $categoryPricename;
}

Natural vs Surrogate keys

It seems like with Doctrine I have to use surrogate keys in my tables to make my design work with Doctrine's limitations.

OR

I could go with mysqli and use natural keys (as in some tables of the ER Diagram now)

Part of me goes... which route do I go, surrogate (Doctrine) or natural (mysqli)

Answer 1

Modeling of more complex relations in Doctrine requires:

1. Model all relations as an entity. Have each such relation entity have a surrogate id primary key.
2. Instead of ManyToMany relation use ManyToOne for each side.

For the above to work, you may need change the structure of your tables to where you have no composite primary keys. That is due to Doctrine does allowing composite primary keys to be associated with foreign ids. It is a limitation. To work with this limitation means having more surrogate keys and less natural keys, which means having more table joins for ie querying price_history .

Alternative way is to use mysqli or PDO.

Alternative way is to not use Doctrine. Set up your tables however you need, and use mysqli or PDO . I chose to go this route because for my design I wanted to use full power of ER Design and DBMS and not have to deal with a lot of table joins.