diff --git a/models/issue.go b/models/issue.go
index 32e6a5b66..8723dda91 100644
--- a/models/issue.go
+++ b/models/issue.go
@@ -1206,8 +1206,12 @@ func Issues(opts *IssuesOptions) ([]*Issue, error) {
 
 // GetParticipantsByIssueID returns all users who are participated in comments of an issue.
 func GetParticipantsByIssueID(issueID int64) ([]*User, error) {
+	return getParticipantsByIssueID(x, issueID)
+}
+
+func getParticipantsByIssueID(e Engine, issueID int64) ([]*User, error) {
 	userIDs := make([]int64, 0, 5)
-	if err := x.Table("comment").Cols("poster_id").
+	if err := e.Table("comment").Cols("poster_id").
 		Where("issue_id = ?", issueID).
 		And("type = ?", CommentTypeComment).
 		Distinct("poster_id").
@@ -1219,7 +1223,7 @@ func GetParticipantsByIssueID(issueID int64) ([]*User, error) {
 	}
 
 	users := make([]*User, 0, len(userIDs))
-	return users, x.In("id", userIDs).Find(&users)
+	return users, e.In("id", userIDs).Find(&users)
 }
 
 // UpdateIssueMentions extracts mentioned people from content and
diff --git a/models/issue_comment.go b/models/issue_comment.go
index 753e79b3d..79fa23960 100644
--- a/models/issue_comment.go
+++ b/models/issue_comment.go
@@ -289,7 +289,7 @@ func (c *Comment) MailParticipants(e Engine, opType ActionType, issue *Issue) (e
 	case ActionReopenIssue:
 		issue.Content = fmt.Sprintf("Reopened #%d", issue.Index)
 	}
-	if err = mailIssueCommentToParticipants(issue, c.Poster, c, mentions); err != nil {
+	if err = mailIssueCommentToParticipants(e, issue, c.Poster, c, mentions); err != nil {
 		log.Error(4, "mailIssueCommentToParticipants: %v", err)
 	}
 
diff --git a/models/issue_mail.go b/models/issue_mail.go
index b9e1a69fc..9e604a50f 100644
--- a/models/issue_mail.go
+++ b/models/issue_mail.go
@@ -22,18 +22,18 @@ func (issue *Issue) mailSubject() string {
 // This function sends two list of emails:
 // 1. Repository watchers and users who are participated in comments.
 // 2. Users who are not in 1. but get mentioned in current issue/comment.
-func mailIssueCommentToParticipants(issue *Issue, doer *User, comment *Comment, mentions []string) error {
+func mailIssueCommentToParticipants(e Engine, issue *Issue, doer *User, comment *Comment, mentions []string) error {
 	if !setting.Service.EnableNotifyMail {
 		return nil
 	}
 
-	watchers, err := GetWatchers(issue.RepoID)
+	watchers, err := getWatchers(e, issue.RepoID)
 	if err != nil {
-		return fmt.Errorf("GetWatchers [repo_id: %d]: %v", issue.RepoID, err)
+		return fmt.Errorf("getWatchers [repo_id: %d]: %v", issue.RepoID, err)
 	}
-	participants, err := GetParticipantsByIssueID(issue.ID)
+	participants, err := getParticipantsByIssueID(e, issue.ID)
 	if err != nil {
-		return fmt.Errorf("GetParticipantsByIssueID [issue_id: %d]: %v", issue.ID, err)
+		return fmt.Errorf("getParticipantsByIssueID [issue_id: %d]: %v", issue.ID, err)
 	}
 
 	// In case the issue poster is not watching the repository,
@@ -54,7 +54,7 @@ func mailIssueCommentToParticipants(issue *Issue, doer *User, comment *Comment,
 			continue
 		}
 
-		to, err := GetUserByID(watchers[i].UserID)
+		to, err := getUserByID(e, watchers[i].UserID)
 		if err != nil {
 			return fmt.Errorf("GetUserByID [%d]: %v", watchers[i].UserID, err)
 		}
@@ -88,7 +88,7 @@ func mailIssueCommentToParticipants(issue *Issue, doer *User, comment *Comment,
 
 		tos = append(tos, mentions[i])
 	}
-	SendIssueMentionMail(issue, doer, comment, GetUserEmailsByNames(tos))
+	SendIssueMentionMail(issue, doer, comment, getUserEmailsByNames(e, tos))
 
 	return nil
 }
@@ -96,12 +96,16 @@ func mailIssueCommentToParticipants(issue *Issue, doer *User, comment *Comment,
 // MailParticipants sends new issue thread created emails to repository watchers
 // and mentioned people.
 func (issue *Issue) MailParticipants() (err error) {
+	return issue.mailParticipants(x)
+}
+
+func (issue *Issue) mailParticipants(e Engine) (err error) {
 	mentions := markdown.FindAllMentions(issue.Content)
-	if err = UpdateIssueMentions(x, issue.ID, mentions); err != nil {
+	if err = UpdateIssueMentions(e, issue.ID, mentions); err != nil {
 		return fmt.Errorf("UpdateIssueMentions [%d]: %v", issue.ID, err)
 	}
 
-	if err = mailIssueCommentToParticipants(issue, issue.Poster, nil, mentions); err != nil {
+	if err = mailIssueCommentToParticipants(e, issue, issue.Poster, nil, mentions); err != nil {
 		log.Error(4, "mailIssueCommentToParticipants: %v", err)
 	}
 
diff --git a/models/user.go b/models/user.go
index bbdec7452..01f14edb7 100644
--- a/models/user.go
+++ b/models/user.go
@@ -1144,11 +1144,15 @@ func GetAssigneeByID(repo *Repository, userID int64) (*User, error) {
 
 // GetUserByName returns user by given name.
 func GetUserByName(name string) (*User, error) {
+	return getUserByName(x, name)
+}
+
+func getUserByName(e Engine, name string) (*User, error) {
 	if len(name) == 0 {
 		return nil, ErrUserNotExist{0, name, 0}
 	}
 	u := &User{LowerName: strings.ToLower(name)}
-	has, err := x.Get(u)
+	has, err := e.Get(u)
 	if err != nil {
 		return nil, err
 	} else if !has {
@@ -1159,9 +1163,13 @@ func GetUserByName(name string) (*User, error) {
 
 // GetUserEmailsByNames returns a list of e-mails corresponds to names.
 func GetUserEmailsByNames(names []string) []string {
+	return getUserEmailsByNames(x, names)
+}
+
+func getUserEmailsByNames(e Engine, names []string) []string {
 	mails := make([]string, 0, len(names))
 	for _, name := range names {
-		u, err := GetUserByName(name)
+		u, err := getUserByName(e, name)
 		if err != nil {
 			continue
 		}