[bugfix] Add proper constraints on status faves, dedupe (#1674)

* [bugfix] Start working on multiple like issue

* finish up

internal/db/bundb/migrations/20230405130021_status_fave_unique_constraints.go

@@ -0,0 +1,166 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package migrations
+
+import (
+	"context"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/uptrace/bun"
+)
+
+func init() {
+	up := func(ctx context.Context, db *bun.DB) error {
+		// To update fave constraints, we need to migrate faves into a new table.
+		// See section 7 here: https://www.sqlite.org/lang_altertable.html
+
+		return db.RunInTx(ctx, nil, func(ctx context.Context, tx bun.Tx) error {
+			// Remove any duplicate faves that were created before constraints.
+			// We need to ensure that we don't just delete all faves that are
+			// duplicates--we should keep the original, non-duplicate fave.
+			// So, produced query will look something like this:
+			//
+			//	DELETE FROM "status_faves"
+			//	WHERE id IN (
+			//		WITH cte AS (
+			//			SELECT
+			//				"id",
+			//				ROW_NUMBER() OVER(
+			//					PARTITION BY "account_id", "status_id"
+			//					ORDER BY "account_id", "status_id"
+			//				) AS "row_number"
+			//			FROM status_faves
+			//		)
+			//		SELECT "id" FROM cte
+			//		WHERE "row_number" > 1
+			//	)
+			//
+			// The above query only deletes status_faves with ids that are
+			// in the subquery. The subquery selects the IDs of all duplicate
+			// status faves past the first one, where 'duplicate' means 'has
+			// the same account id and status id'.
+			overQ := tx.NewRaw(
+				"PARTITION BY ?, ? ORDER BY ?, ?",
+				bun.Ident("account_id"),
+				bun.Ident("status_id"),
+				bun.Ident("account_id"),
+				bun.Ident("status_id"),
+			)
+
+			rowNumberQ := tx.NewRaw(
+				"SELECT ?, ROW_NUMBER() OVER(?) AS ? FROM status_faves",
+				bun.Ident("id"),
+				overQ,
+				bun.Ident("row_number"),
+			)
+
+			inQ := tx.NewRaw(
+				"WITH cte AS (?) SELECT ? FROM cte WHERE ? > 1",
+				rowNumberQ,
+				bun.Ident("id"),
+				bun.Ident("row_number"),
+			)
+
+			if _, err := tx.
+				NewDelete().
+				Table("status_faves").
+				Where("id IN (?)", inQ).
+				Exec(ctx); err != nil {
+				return err
+			}
+
+			// Create the new faves table.
+			if _, err := tx.
+				NewCreateTable().
+				ModelTableExpr("new_status_faves").
+				Model(&gtsmodel.StatusFave{}).
+				Exec(ctx); err != nil {
+				return err
+			}
+
+			// Specify columns explicitly to
+			// avoid any Postgres shenanigans.
+			columns := []string{
+				"id",
+				"created_at",
+				"updated_at",
+				"account_id",
+				"target_account_id",
+				"status_id",
+				"uri",
+			}
+
+			// Copy remaining faves to the new table.
+			if _, err := tx.
+				NewInsert().
+				Table("new_status_faves").
+				Table("status_faves").
+				Column(columns...).
+				Exec(ctx); err != nil {
+				return err
+			}
+
+			// Drop the old table.
+			if _, err := tx.
+				NewDropTable().
+				Table("status_faves").
+				Exec(ctx); err != nil {
+				return err
+			}
+
+			// Rename new table to old table.
+			if _, err := tx.
+				ExecContext(
+					ctx,
+					"ALTER TABLE ? RENAME TO ?",
+					bun.Ident("new_status_faves"),
+					bun.Ident("status_faves"),
+				); err != nil {
+				return err
+			}
+
+			// Add indexes to the new table.
+			for index, columns := range map[string][]string{
+				"status_faves_id_idx":         {"id"},
+				"status_faves_account_id_idx": {"account_id"},
+				"status_faves_status_id_idx":  {"status_id"},
+			} {
+				if _, err := tx.
+					NewCreateIndex().
+					Table("status_faves").
+					Index(index).
+					Column(columns...).
+					Exec(ctx); err != nil {
+					return err
+				}
+			}
+
+			return nil
+		})
+	}
+
+	down := func(ctx context.Context, db *bun.DB) error {
+		return db.RunInTx(ctx, nil, func(ctx context.Context, tx bun.Tx) error {
+			return nil
+		})
+	}
+
+	if err := Migrations.Register(up, down); err != nil {
+		panic(err)
+	}
+}