feat(models): extend claim with Claim and Comment

examples/blog/app/models/claim.rb

@@ -0,0 +1,22 @@
+class Claim < Prism::Orm::Model
+  # counter_cache keeps Post#claims_count (and therefore
+  # Post#giveaway_remaining/#giveaway_sold_out?) O(1) to read - the whole
+  # point of ClaimsController#create locking the post first is to make that
+  # read-then-decide safe under concurrency, which would be undermined if
+  # the read itself required walking every Claim row instead.
+  belongs_to :post, counter_cache: true
+  belongs_to :user
+
+  # Not a user-facing "unclaim" - a claim has no destroy action anywhere in
+  # this app (see ClaimsController, create-only). Paranoid purely so
+  # Post#acts_as_paranoid's `dependent: :destroy` cascade (see the model)
+  # soft-deletes a giveaway's claims along with a trashed post instead of
+  # erasing the record of who already won a slot, and #restore(recursive:
+  # true) brings them back - same shape as Comment/Like.
+  acts_as_paranoid
+
+  # One claim per user per post - see the unique index on [:post_id,
+  # :user_id] in the create_claims migration for the same rule enforced at
+  # the Store level too, inside whatever transaction the insert runs in.
+  validates :user_id, presence: true, uniqueness: { scope: :post_id }
+end