tl;dr
I need an edit form for a uni-directional many-to-many relationship (doctrine), where the resulting join table has extra inherited properties. Is there a way to achieve this through the FormBuilder?
Entities
I have a uni-directional many-to-many relationship (doctrine), where the resulting join table has a relation to a third entity.
Form
The User edit-form should allow (un)crossing Deals easily through a checkbox, while also showing the relations' inherited fields from Discount. The discount's properties should be inherited from Deal by default and overridden on the UserDeal object if modified.
My approach
The way I have approached this, is by creating an auxiliary object UserDealState with two properties: a boolean active and a reference to the UserDeal. UserDealState has its own Type (checkbox and Discount fields).
I also added a transformer that converts the array of UserDeals to an array of UserDealStates, adding all the non-joined Deals (and setting active to false).
When I check the form inspector in the Symfony Profiler, I can see the transformation has taken place (the view data holds a collection of UserDealStates and is a much longer collection than the model data that holds a collection of UserDeals, which makes sense), but the form object only holds the amount of UserDealStates formViews that the original collection had of UserDeals had, not the much larger number it should.
Just to give a concrete example: say we have 10 Deals, and only one crossed UserDeals. On my form {{ form.userDeals.vars.value|length }} returns 10, {{ form.userDeals.children|length }} returns 1. Only one subform is rendered instead of 10.
Hera are my form-types: UserType, UserDealStateType, UserDealType, DiscountType.
Transformer: UserDealStateToUserDealTransformer
The question
How do you render a form with FormBuilder to edit the mapping between two entities in a many-to-many relationship and the relations' extra fields (as shown on the form mock-up above)?