DDC-2772: One class can be mapped to multiple discriminator values

[doctrinebot]

Jira issue originally created by user mouyang:

I'm not sure if this is intentional or not, but this appears to a valid discriminator map. The problem I am running into is that it's impossible to create an instance of ClassB with a discriminator value "DiscB" (it's always "DiscC" - I'm assuming last one wins here).

<entity name="ClassB" ...>
  <discriminator-map>
    <discriminator-mapping value="DiscA" class="ClassA" />
    <discriminator-mapping value="DiscB" class="ClassB" />
    <discriminator-mapping value="DiscC" class="ClassB" />
  </discriminator-map>
</entity>

Eventhough DiscB and DiscC map to the same class, I do want to maintain some sort of logical separation in the database using the two discriminator values. That does not appear to be possible. I can provide more details about my data model, if necessary.

These are the possible solutions I can think of.

1. Enforce a strict one-to-one relationship between value and class. This means I would have to modify my code to reflect this.
2. (I know this has been rejected before, but I'm in favour of this solution.) Expose the discriminator field but validate it before committing to the database. I'm actually using the discriminator as part of a compound primary key, so this would be very helpful to me.

[guilhermeblanco]

Our intended solution is 1. "Enforce a strict one-to-one relationship between value and class. This means I would have to modify my code to reflect this."

An enforcement should be added restricting people to map multiple discriminator values to a single class. This should be done at mapping level by checking count(array_unique($map)) === count($map) and adding a MappingException if it doesn't match.

[beberlei]

This makes sense for ORM 3.0 but also requires a deprecation message to be thrown in 2.x

[derrabus]

Do you want to work on it? 🙃

[javijavo]

Hello,
I would like to ask why is this not possible?
If I have a let's say two possible classes Mammals and Reptiles and I want to discriminate "cat", "dog" to Mammals and "turtle" to Reptile? How do we do it after this deprecation?

(The example is very basic but I have some entity that works thay way)

Thanks

[beberlei]

@javijavo but there is no way to new Mamal() and have it stored as either dog or cat. Do you create these entities outside the ORM?

[javijavo]

I have a very old and huge legacy application progressively adating it to Doctrine and yes the data is already stored.

But I see the problem of having multiple values, didn't have in mind the "standard" scenario instead my ugly one.
Will look for another way to meet my requirements.

Thanks