Split migrations folder (#21549)

There are too many files in `models/migrations` folder so that I split
them into sub folders.

models/migrations/v1_14/v157.go

@@ -0,0 +1,67 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package v1_14 //nolint
+
+import (
+	"xorm.io/xorm"
+)
+
+func FixRepoTopics(x *xorm.Engine) error {
+	type Topic struct {
+		ID        int64  `xorm:"pk autoincr"`
+		Name      string `xorm:"UNIQUE VARCHAR(25)"`
+		RepoCount int
+	}
+
+	type RepoTopic struct {
+		RepoID  int64 `xorm:"pk"`
+		TopicID int64 `xorm:"pk"`
+	}
+
+	type Repository struct {
+		ID     int64    `xorm:"pk autoincr"`
+		Topics []string `xorm:"TEXT JSON"`
+	}
+
+	const batchSize = 100
+	sess := x.NewSession()
+	defer sess.Close()
+	repos := make([]*Repository, 0, batchSize)
+	topics := make([]string, 0, batchSize)
+	for start := 0; ; start += batchSize {
+		repos = repos[:0]
+
+		if err := sess.Begin(); err != nil {
+			return err
+		}
+
+		if err := sess.Limit(batchSize, start).Find(&repos); err != nil {
+			return err
+		}
+
+		if len(repos) == 0 {
+			break
+		}
+
+		for _, repo := range repos {
+			topics = topics[:0]
+			if err := sess.Select("name").Table("topic").
+				Join("INNER", "repo_topic", "repo_topic.topic_id = topic.id").
+				Where("repo_topic.repo_id = ?", repo.ID).Desc("topic.repo_count").Find(&topics); err != nil {
+				return err
+			}
+			repo.Topics = topics
+			if _, err := sess.ID(repo.ID).Cols("topics").Update(repo); err != nil {
+				return err
+			}
+		}
+
+		if err := sess.Commit(); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}