protoc-gen-entgrpc: mutating methods should regard null/zero values and field nullability

[rotemtam]

Summary 💡

Currently protoc-gen-entgrpc does not consider zero/nil values in the generated Create and Update methods.
For example, the Create method will Set all available fields:

res, err := svc.client.User.Create().
  SetExp(uint64(user.GetExp())).
  SetJoined(entproto.ExtractTime(user.GetJoined())).
  SetPoints(uint(user.GetPoints())).
  SetStatus(toEntUser_Status(user.GetStatus())).
  SetUserName(string(user.GetUserName())).
  SetGroupID(int(user.GetGroup().GetId())).
  Save(ctx)

If for example, the Joined field has a default value, the user has no way to pass a nil/zero value to let ent use the default for the field.

In addition, if the calling user does not set a Group with a valid ID, the generated code will execute .SetGroupId(0), which will cause the insert to fail on a foreign key constraint, since no Group with ID zero exists.

[rotemtam]

My initial thought on this is to use proto 3 Wrapper types instead of primitives for fields that are Nillable and then to check for presence before invoking the ent Set<Field>.

WDYT @Bladrak @tmc @godcong ?

[Bladrak]

Looks like a good insight indeed 👍