From fa2b97242dcd00ece6174b87043769651153fe82 Mon Sep 17 00:00:00 2001
From: Nazar Kanaev <nkanaev@live.com>
Date: Wed, 10 Mar 2021 21:58:00 +0000
Subject: [PATCH] storage fixes

---
 src/server/crawler.go    |  4 +--
 src/storage/item.go      |  2 +-
 src/storage/migration.go | 77 +++++++++++++++++++++++++---------------
 3 files changed, 52 insertions(+), 31 deletions(-)

diff --git a/src/server/crawler.go b/src/server/crawler.go
index 3351027..946f798 100644
--- a/src/server/crawler.go
+++ b/src/server/crawler.go
@@ -238,11 +238,11 @@ func convertItems(items []*gofeed.Item, feed storage.Feed) []storage.Item {
 		if item.Author != nil {
 			author = item.Author.Name
 		}
-		podcastUrl := ""
+		var podcastUrl *string
 		if item.Enclosures != nil {
 			for _, enclosure := range item.Enclosures {
 				if strings.ToLower(enclosure.Type) == "audio/mpeg" {
-					podcastUrl = enclosure.URL
+					podcastUrl = &enclosure.URL
 				}
 			}
 		}
diff --git a/src/storage/item.go b/src/storage/item.go
index 4a1eaab..b37a328 100644
--- a/src/storage/item.go
+++ b/src/storage/item.go
@@ -55,7 +55,7 @@ type Item struct {
 	DateUpdated *time.Time `json:"date_updated"`
 	Status      ItemStatus `json:"status"`
 	Image       string     `json:"image"`
-	PodcastURL  string     `json:"podcast_url"`
+	PodcastURL  *string    `json:"podcast_url"`
 }
 
 type ItemFilter struct {
diff --git a/src/storage/migration.go b/src/storage/migration.go
index 63ecdf9..67ecbe2 100644
--- a/src/storage/migration.go
+++ b/src/storage/migration.go
@@ -26,34 +26,58 @@ func migrate(db *sql.DB, log *log.Logger) error {
 	log.Printf("db version is %d. migrating to %d", version, maxVersion)
 
 	for v := version + 1; v <= maxVersion; v++ {
-		migratefunc := migrations[v - 1]
-		var tx *sql.Tx
-		var err error
+		// Migrations altering schema using a sequence of steps due to SQLite limitations.
+		// Must come with `pragma foreign_key_check` at the end. See:
+		// "Making Other Kinds Of Table Schema Changes"
+	    // https://www.sqlite.org/lang_altertable.html
+		trickyAlteration := (v == 3)
 
 		log.Printf("[migration:%d] starting", v)
-		if tx, err = db.Begin(); err != nil {
-			log.Printf("[migration:%d] failed to start transaction", v)
-			return err
-		}
-		if err = migratefunc(tx); err != nil {
-			log.Printf("[migration:%d] failed to migrate", v)
-			tx.Rollback()
-			return err
-		}
-		if _, err = tx.Exec(fmt.Sprintf("pragma user_version = %d", v)); err != nil {
-			log.Printf("[migration:%d] failed to bump version", v)
-			tx.Rollback()
-			return err
-		}
-		if err = tx.Commit(); err != nil {
-			log.Printf("[migration:%d] failed to commit changes", v)
+
+		if trickyAlteration {
+			db.Exec("pragma foreign_keys=off;")
+		}
+
+		err := migrateVersion(v, db)
+
+		if trickyAlteration {
+			db.Exec("pragma foreign_keys=on;")
+		}
+
+		if err != nil {
 			return err
 		}
+
 		log.Printf("[migration:%d] done", v)
 	}
 	return nil
 }
 
+func migrateVersion(v int64, db *sql.DB) error {
+	var err error
+	var tx *sql.Tx
+	migratefunc := migrations[v - 1]
+	if tx, err = db.Begin(); err != nil {
+		log.Printf("[migration:%d] failed to start transaction", v)
+		return err
+	}
+	if err = migratefunc(tx); err != nil {
+		log.Printf("[migration:%d] failed to migrate", v)
+		tx.Rollback()
+		return err
+	}
+	if _, err = tx.Exec(fmt.Sprintf("pragma user_version = %d", v)); err != nil {
+		log.Printf("[migration:%d] failed to bump version", v)
+		tx.Rollback()
+		return err
+	}
+	if err = tx.Commit(); err != nil {
+		log.Printf("[migration:%d] failed to commit changes", v)
+		return err
+	}
+	return nil
+}
+
 func m01_initial(tx *sql.Tx) error {
 	sql := `
 		create table if not exists folders (
@@ -136,10 +160,7 @@ func m02_feed_states_and_errors(tx *sql.Tx) error {
 
 func m03_on_delete_actions(tx *sql.Tx) error {
 	sql := `
-		-- 01. disable foreignkey constraint
-		pragma foreign_keys=off;
-
-		-- 02. create altered tables
+		-- 01. create altered tables
 		create table if not exists new_feeds (
 		 id             integer primary key autoincrement,
 		 folder_id      references folders(id) on delete set null,
@@ -176,25 +197,25 @@ func m03_on_delete_actions(tx *sql.Tx) error {
 		 error          string
 		);
 
-		-- 03. transfer content into new tables
+		-- 02. transfer data into new tables
 		insert into new_feeds select * from feeds;
 		insert into new_items select * from items;
 		insert into new_http_states select * from http_states;
 		insert into new_feed_errors select * from feed_errors;
 
-		-- 04. drop old tables
+		-- 03. drop old tables
 		drop table feeds;
 		drop table items;
 		drop table http_states;
 		drop table feed_errors;
 
-		-- 05. rename new tables
+		-- 04. rename new tables
 		alter table new_feeds rename to feeds;
 		alter table new_items rename to items;
 		alter table new_http_states rename to http_states;
 		alter table new_feed_errors rename to feed_errors;
 
-		-- 06. reconstruct indexes & triggers
+		-- 05. reconstruct indexes & triggers
 		create index if not exists idx_feed_folder_id on feeds(folder_id);
 		create unique index if not exists idx_feed_feed_link on feeds(feed_link);
 		create index if not exists idx_item_feed_id on items(feed_id);
@@ -205,8 +226,8 @@ func m03_on_delete_actions(tx *sql.Tx) error {
 		  delete from search where rowid = old.search_rowid;
 		end;
 
+		-- 06. check consistency
 		pragma foreign_key_check;
-		pragma foreign_keys=on;
 	`
 	_, err := tx.Exec(sql)
 	return err