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If Joe sends an invitation to Alice, and later in the day Fred also sends an invite to Alice, we lose the information that Joe sent the initial invite. There's only one invited_by field, and the value stored there is the last inviter.
This doesn't meet the requirements for my application because we give credit to members for inviting other members. When Alice accepts the invitation, the second inviter, Fred, receives credit. Joe should also receive credit.
The best way to fix this would be to create a separate table for invitations. invited_by would become a has_many :through relationship rather than a belongs_to relationship. Invitations would belong_to inviter and also belong_to resource. So Invitations would be a many-to-many mapping table.
This may be more complication than you want to get into for the gem, but I'm not sure of another good way to fix this problem. A lot of sites want to give users credit for invites, so this seems like something that would be useful.
Thanks for the gem!
Are there any plans for doing something like this?