Move db related basic functions to models/db (#17075)

* Move db related basic functions to models/db

* Fix lint

* Fix lint

* Fix test

* Fix lint

* Fix lint

* revert unnecessary change

* Fix test

* Fix wrong replace string

* Use *Context

* Correct committer spelling and fix wrong replaced words

Co-authored-by: zeripath <art27@cantab.net>

1 files changed, 110 insertions, 0 deletions

diff --git a/models/db/index.go b/models/db/index.go
new file mode 100644
index 0000000000..873289db54
--- /dev/null
+++ b/models/db/index.go
@@ -0,0 +1,110 @@
+// Copyright 2021 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 db
+
+import (
+	"errors"
+	"fmt"
+
+	"code.gitea.io/gitea/modules/setting"
+)
+
+// ResourceIndex represents a resource index which could be used as issue/release and others
+// We can create different tables i.e. issue_index, release_index and etc.
+type ResourceIndex struct {
+	GroupID  int64 `xorm:"pk"`
+	MaxIndex int64 `xorm:"index"`
+}
+
+// UpsertResourceIndex the function will not return until it acquires the lock or receives an error.
+func UpsertResourceIndex(e Engine, tableName string, groupID int64) (err error) {
+	// An atomic UPSERT operation (INSERT/UPDATE) is the only operation
+	// that ensures that the key is actually locked.
+	switch {
+	case setting.Database.UseSQLite3 || setting.Database.UsePostgreSQL:
+		_, err = e.Exec(fmt.Sprintf("INSERT INTO %s (group_id, max_index) "+
+			"VALUES (?,1) ON CONFLICT (group_id) DO UPDATE SET max_index = %s.max_index+1",
+			tableName, tableName), groupID)
+	case setting.Database.UseMySQL:
+		_, err = e.Exec(fmt.Sprintf("INSERT INTO %s (group_id, max_index) "+
+			"VALUES (?,1) ON DUPLICATE KEY UPDATE max_index = max_index+1", tableName),
+			groupID)
+	case setting.Database.UseMSSQL:
+		// https://weblogs.sqlteam.com/dang/2009/01/31/upsert-race-condition-with-merge/
+		_, err = e.Exec(fmt.Sprintf("MERGE %s WITH (HOLDLOCK) as target "+
+			"USING (SELECT ? AS group_id) AS src "+
+			"ON src.group_id = target.group_id "+
+			"WHEN MATCHED THEN UPDATE SET target.max_index = target.max_index+1 "+
+			"WHEN NOT MATCHED THEN INSERT (group_id, max_index) "+
+			"VALUES (src.group_id, 1);", tableName),
+			groupID)
+	default:
+		return fmt.Errorf("database type not supported")
+	}
+	return
+}
+
+var (
+	// ErrResouceOutdated represents an error when request resource outdated
+	ErrResouceOutdated = errors.New("resource outdated")
+	// ErrGetResourceIndexFailed represents an error when resource index retries 3 times
+	ErrGetResourceIndexFailed = errors.New("get resource index failed")
+)
+
+const (
+	maxDupIndexAttempts = 3
+)
+
+// GetNextResourceIndex retried 3 times to generate a resource index
+func GetNextResourceIndex(tableName string, groupID int64) (int64, error) {
+	for i := 0; i < maxDupIndexAttempts; i++ {
+		idx, err := getNextResourceIndex(tableName, groupID)
+		if err == ErrResouceOutdated {
+			continue
+		}
+		if err != nil {
+			return 0, err
+		}
+		return idx, nil
+	}
+	return 0, ErrGetResourceIndexFailed
+}
+
+// DeleteResouceIndex delete resource index
+func DeleteResouceIndex(e Engine, tableName string, groupID int64) error {
+	_, err := e.Exec(fmt.Sprintf("DELETE FROM %s WHERE group_id=?", tableName), groupID)
+	return err
+}
+
+// getNextResourceIndex return the next index
+func getNextResourceIndex(tableName string, groupID int64) (int64, error) {
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return 0, err
+	}
+	var preIdx int64
+	_, err := sess.SQL(fmt.Sprintf("SELECT max_index FROM %s WHERE group_id = ?", tableName), groupID).Get(&preIdx)
+	if err != nil {
+		return 0, err
+	}
+
+	if err := UpsertResourceIndex(sess, tableName, groupID); err != nil {
+		return 0, err
+	}
+
+	var curIdx int64
+	has, err := sess.SQL(fmt.Sprintf("SELECT max_index FROM %s WHERE group_id = ? AND max_index=?", tableName), groupID, preIdx+1).Get(&curIdx)
+	if err != nil {
+		return 0, err
+	}
+	if !has {
+		return 0, ErrResouceOutdated
+	}
+	if err := sess.Commit(); err != nil {
+		return 0, err
+	}
+	return curIdx, nil
+}