[PORT] gitea#30190: Add unique index for project_issue to prevent duplicate data

Fix #27639

---

Remove MSSQL specific code per https://codeberg.org/forgejo/discussions/issues/122

(cherry picked from commit b4825670596fe745cebdcc63a8ead4388602d42c)

models/migrations/v1_23/v294.go

@@ -0,0 +1,44 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_23 //nolint
+
+import (
+	"xorm.io/xorm"
+)
+
+// AddUniqueIndexForProjectIssue adds unique indexes for project issue table
+func AddUniqueIndexForProjectIssue(x *xorm.Engine) error {
+	// remove possible duplicated records in table project_issue
+	type result struct {
+		IssueID   int64
+		ProjectID int64
+		Cnt       int
+	}
+	var results []result
+	if err := x.Select("issue_id, project_id, count(*) as cnt").
+		Table("project_issue").
+		GroupBy("issue_id, project_id").
+		Having("count(*) > 1").
+		Find(&results); err != nil {
+		return err
+	}
+	for _, r := range results {
+		var ids []int64
+		if err := x.SQL("SELECT id FROM project_issue WHERE issue_id = ? and project_id = ? limit ?", r.IssueID, r.ProjectID, r.Cnt-1).Find(&ids); err != nil {
+			return err
+		}
+		if _, err := x.Table("project_issue").In("id", ids).Delete(); err != nil {
+			return err
+		}
+	}
+
+	// add unique index for project_issue table
+	type ProjectIssue struct { //revive:disable-line:exported
+		ID        int64 `xorm:"pk autoincr"`
+		IssueID   int64 `xorm:"INDEX unique(s)"`
+		ProjectID int64 `xorm:"INDEX unique(s)"`
+	}
+
+	return x.Sync(new(ProjectIssue))
+}