feat: add book reviews

backend/drizzle/20261110140402_book_reviews/migration.sql

@@ -0,0 +1,22 @@
+CREATE TABLE "book_reviews" (
+	"id" integer PRIMARY KEY GENERATED ALWAYS AS IDENTITY (sequence name "book_reviews_id_seq" INCREMENT BY 1 MINVALUE 1 MAXVALUE 2147483647 START WITH 1 CACHE 1),
+	"user_id" text NOT NULL,
+	"book_id" integer NOT NULL,
+	"rating" smallint NOT NULL,
+	"comment" text,
+	"created_at" timestamp DEFAULT now() NOT NULL,
+	"updated_at" timestamp DEFAULT now() NOT NULL,
+	CONSTRAINT "book_reviews_user_id_book_id_unique" UNIQUE("user_id","book_id"),
+	CONSTRAINT "book_reviews_rating_check" CHECK ("rating" between 1 and 5)
+);
+--> statement-breakpoint
+ALTER TABLE "books" ADD COLUMN "initial_rating" real;--> statement-breakpoint
+ALTER TABLE "books" ADD COLUMN "initial_num_ratings" integer;--> statement-breakpoint
+CREATE INDEX "book_reviews_book_id_created_at_idx" ON "book_reviews" ("book_id","created_at");--> statement-breakpoint
+CREATE INDEX "book_reviews_user_id_created_at_idx" ON "book_reviews" ("user_id","created_at");--> statement-breakpoint
+ALTER TABLE "book_reviews" ADD CONSTRAINT "book_reviews_user_id_user_id_fkey" FOREIGN KEY ("user_id") REFERENCES "user"("id") ON DELETE CASCADE;--> statement-breakpoint
+ALTER TABLE "book_reviews" ADD CONSTRAINT "book_reviews_book_id_books_id_fkey" FOREIGN KEY ("book_id") REFERENCES "books"("id") ON DELETE CASCADE;--> statement-breakpoint
+
+-- Custom SQL: the existing rating columns hold the dataset values, so copy them to the new initial columns.
+-- There are no user reviews yet, so rating and num_ratings already hold the correct values.
+UPDATE "books" SET "initial_rating" = "rating", "initial_num_ratings" = "num_ratings";