[Form] DoctrineOrmTypeGuesser causes error for DecimalType

[ricohumme]

Symfony version(s) affected: 4.3.0

Description
The TypeGuesser (DoctrineOrmTypeGuesser) sets the option input to string which causes the StringToFloatTransformer to take effect. Passing a float from the model to the form causes the transformation to fail

Possible Solution
Remove the option input: string from the TypeGuesser or allow values which are already a float to pass the transformer.
Why this option is added for a DecimalType (as a default) in the first place is a riddle to me.

[xabbuh]

This is expected behaviour. The decimal type maps values to a PHP string (see https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/basic-mapping.html#doctrine-mapping-types).

[ricohumme]

Expected as it may be regarding the doctrine mapping, the transformer introduces a BC break here. In that case I would expect the transformer to pass when the value enters the transformer as a float.
Wouldn’t you agree?

[xabbuh]

I would first investigate why your data is a float in the first place as it's probably even not guaranteed that it will work with Doctrine in all cases.

As a quick workaround you can probably also add the input option of your form type to number explicitly to not rely on the guessing of the option.

[ricohumme]

Well, to the why it is a float is simple, the model says it is a float and the return type of the method as well as the declaration of the property is configured that way.

I have in fact implemented the field with the number type in the form explicitly now so the pressure is off at the moment.
However, this is the case for one of our projects. We use a generic form which relies on the guesser to pass correct information and in this case an assumption is made which is false imo.

But I’m interested to hear what others think.

[ricohumme]

After discussing this with my colleague I tried to alter the type of my model from Decimal to Float and the following came to light:
Previous:
Model:
@ORM\Column(type="decimal", precision=9, scale=2, nullable=true)
Database:
Datatype: DECIMAL(9,2)

After:
Model:
@ORM\Column(type="float", precision=9, scale=2, nullable=true)
Database:
Datatype: DOUBLE

As long as the precision and scale are defined, the form enforces the values to meet these demands, however on database level these constraints are no longer present.
I have yet to test what would happen if the value is updated through the model without a form. Updating the value directly in the database shows there is no restriction for decimals.

[xabbuh]

See #32125 where we try to relax the data transformer. Does that help here?

[ricohumme]

I think this will do the trick. Let me test this tomorrow