Implement a code action adding a unique constraint to a relation

[pimeys]

Problem

Let's consider the following data model:

model Foo {
  id  Int   @id
  val Int
  Bar Bar[]
}

model Bar {
  id    Int @id
  fooId Int
  foo   Foo @relation(fields: [fooId], references: [val])
}

The relation gives a validation error:

error: Error parsing attribute "@relation": The argument `references` must refer to a unique criteria in the related model. Consider adding an `@unique` attribute to the field `val` in the model `Foo`.
  -->  schema.prisma:15
   | 
14 |   fooId Int
15 |   foo   Foo @relation(fields: [fooId], references: [val])
16 | }
   | 

It is hard to find in some cases the place where to add the needed constraint.

Suggested solution

Implement a code action to add the unique constraint to the correct position. This should also work with compound keys, adding a @@unique attribute to the correct model.