Performance improvements for pull request list API (#30490)

Fix #30483

---------

Co-authored-by: yp05327 <576951401@qq.com>
Co-authored-by: Giteabot <teabot@gitea.io>

8 files changed, 184 insertions, 101 deletions

diff --git a/models/issues/assignees.go b/models/issues/assignees.go
index 30234be07a..efd992cda2 100644
--- a/models/issues/assignees.go
+++ b/models/issues/assignees.go
@@ -27,23 +27,27 @@ func init() {
 
 // LoadAssignees load assignees of this issue.
 func (issue *Issue) LoadAssignees(ctx context.Context) (err error) {
+	if issue.isAssigneeLoaded || len(issue.Assignees) > 0 {
+		return nil
+	}
+
 	// Reset maybe preexisting assignees
 	issue.Assignees = []*user_model.User{}
 	issue.Assignee = nil
 
-	err = db.GetEngine(ctx).Table("`user`").
+	if err = db.GetEngine(ctx).Table("`user`").
 		Join("INNER", "issue_assignees", "assignee_id = `user`.id").
 		Where("issue_assignees.issue_id = ?", issue.ID).
-		Find(&issue.Assignees)
-	if err != nil {
+		Find(&issue.Assignees); err != nil {
 		return err
 	}
 
+	issue.isAssigneeLoaded = true
 	// Check if we have at least one assignee and if yes put it in as `Assignee`
 	if len(issue.Assignees) > 0 {
 		issue.Assignee = issue.Assignees[0]
 	}
-	return err
+	return nil
 }
 
 // GetAssigneeIDsByIssue returns the IDs of users assigned to an issue
diff --git a/models/issues/comment_list.go b/models/issues/comment_list.go
index 370b5396e0..6b4ad80eed 100644
--- a/models/issues/comment_list.go
+++ b/models/issues/comment_list.go
@@ -16,19 +16,17 @@ import (
 // CommentList defines a list of comments
 type CommentList []*Comment
 
-func (comments CommentList) getPosterIDs() []int64 {
-	return container.FilterSlice(comments, func(c *Comment) (int64, bool) {
-		return c.PosterID, c.PosterID > 0
-	})
-}
-
 // LoadPosters loads posters
 func (comments CommentList) LoadPosters(ctx context.Context) error {
 	if len(comments) == 0 {
 		return nil
 	}
 
-	posterMaps, err := getPosters(ctx, comments.getPosterIDs())
+	posterIDs := container.FilterSlice(comments, func(c *Comment) (int64, bool) {
+		return c.PosterID, c.Poster == nil && c.PosterID > 0
+	})
+
+	posterMaps, err := getPostersByIDs(ctx, posterIDs)
 	if err != nil {
 		return err
 	}
diff --git a/models/issues/issue.go b/models/issues/issue.go
index aad855522d..40462ed09d 100644
--- a/models/issues/issue.go
+++ b/models/issues/issue.go
@@ -98,32 +98,35 @@ var ErrIssueAlreadyChanged = util.NewInvalidArgumentErrorf("the issue is already
 
 // Issue represents an issue or pull request of repository.
 type Issue struct {
-	ID               int64                  `xorm:"pk autoincr"`
-	RepoID           int64                  `xorm:"INDEX UNIQUE(repo_index)"`
-	Repo             *repo_model.Repository `xorm:"-"`
-	Index            int64                  `xorm:"UNIQUE(repo_index)"` // Index in one repository.
-	PosterID         int64                  `xorm:"INDEX"`
-	Poster           *user_model.User       `xorm:"-"`
-	OriginalAuthor   string
-	OriginalAuthorID int64                  `xorm:"index"`
-	Title            string                 `xorm:"name"`
-	Content          string                 `xorm:"LONGTEXT"`
-	RenderedContent  template.HTML          `xorm:"-"`
-	ContentVersion   int                    `xorm:"NOT NULL DEFAULT 0"`
-	Labels           []*Label               `xorm:"-"`
-	MilestoneID      int64                  `xorm:"INDEX"`
-	Milestone        *Milestone             `xorm:"-"`
-	Project          *project_model.Project `xorm:"-"`
-	Priority         int
-	AssigneeID       int64            `xorm:"-"`
-	Assignee         *user_model.User `xorm:"-"`
-	IsClosed         bool             `xorm:"INDEX"`
-	IsRead           bool             `xorm:"-"`
-	IsPull           bool             `xorm:"INDEX"` // Indicates whether is a pull request or not.
-	PullRequest      *PullRequest     `xorm:"-"`
-	NumComments      int
-	Ref              string
-	PinOrder         int `xorm:"DEFAULT 0"`
+	ID                int64                  `xorm:"pk autoincr"`
+	RepoID            int64                  `xorm:"INDEX UNIQUE(repo_index)"`
+	Repo              *repo_model.Repository `xorm:"-"`
+	Index             int64                  `xorm:"UNIQUE(repo_index)"` // Index in one repository.
+	PosterID          int64                  `xorm:"INDEX"`
+	Poster            *user_model.User       `xorm:"-"`
+	OriginalAuthor    string
+	OriginalAuthorID  int64                  `xorm:"index"`
+	Title             string                 `xorm:"name"`
+	Content           string                 `xorm:"LONGTEXT"`
+	RenderedContent   template.HTML          `xorm:"-"`
+	ContentVersion    int                    `xorm:"NOT NULL DEFAULT 0"`
+	Labels            []*Label               `xorm:"-"`
+	isLabelsLoaded    bool                   `xorm:"-"`
+	MilestoneID       int64                  `xorm:"INDEX"`
+	Milestone         *Milestone             `xorm:"-"`
+	isMilestoneLoaded bool                   `xorm:"-"`
+	Project           *project_model.Project `xorm:"-"`
+	Priority          int
+	AssigneeID        int64            `xorm:"-"`
+	Assignee          *user_model.User `xorm:"-"`
+	isAssigneeLoaded  bool             `xorm:"-"`
+	IsClosed          bool             `xorm:"INDEX"`
+	IsRead            bool             `xorm:"-"`
+	IsPull            bool             `xorm:"INDEX"` // Indicates whether is a pull request or not.
+	PullRequest       *PullRequest     `xorm:"-"`
+	NumComments       int
+	Ref               string
+	PinOrder          int `xorm:"DEFAULT 0"`
 
 	DeadlineUnix timeutil.TimeStamp `xorm:"INDEX"`
 
@@ -131,11 +134,12 @@ type Issue struct {
 	UpdatedUnix timeutil.TimeStamp `xorm:"INDEX updated"`
 	ClosedUnix  timeutil.TimeStamp `xorm:"INDEX"`
 
-	Attachments      []*repo_model.Attachment `xorm:"-"`
-	Comments         CommentList              `xorm:"-"`
-	Reactions        ReactionList             `xorm:"-"`
-	TotalTrackedTime int64                    `xorm:"-"`
-	Assignees        []*user_model.User       `xorm:"-"`
+	Attachments         []*repo_model.Attachment `xorm:"-"`
+	isAttachmentsLoaded bool                     `xorm:"-"`
+	Comments            CommentList              `xorm:"-"`
+	Reactions           ReactionList             `xorm:"-"`
+	TotalTrackedTime    int64                    `xorm:"-"`
+	Assignees           []*user_model.User       `xorm:"-"`
 
 	// IsLocked limits commenting abilities to users on an issue
 	// with write access
@@ -187,6 +191,19 @@ func (issue *Issue) LoadRepo(ctx context.Context) (err error) {
 	return nil
 }
 
+func (issue *Issue) LoadAttachments(ctx context.Context) (err error) {
+	if issue.isAttachmentsLoaded || issue.Attachments != nil {
+		return nil
+	}
+
+	issue.Attachments, err = repo_model.GetAttachmentsByIssueID(ctx, issue.ID)
+	if err != nil {
+		return fmt.Errorf("getAttachmentsByIssueID [%d]: %w", issue.ID, err)
+	}
+	issue.isAttachmentsLoaded = true
+	return nil
+}
+
 // IsTimetrackerEnabled returns true if the repo enables timetracking
 func (issue *Issue) IsTimetrackerEnabled(ctx context.Context) bool {
 	if err := issue.LoadRepo(ctx); err != nil {
@@ -287,11 +304,12 @@ func (issue *Issue) loadReactions(ctx context.Context) (err error) {
 
 // LoadMilestone load milestone of this issue.
 func (issue *Issue) LoadMilestone(ctx context.Context) (err error) {
-	if (issue.Milestone == nil || issue.Milestone.ID != issue.MilestoneID) && issue.MilestoneID > 0 {
+	if !issue.isMilestoneLoaded && (issue.Milestone == nil || issue.Milestone.ID != issue.MilestoneID) && issue.MilestoneID > 0 {
 		issue.Milestone, err = GetMilestoneByRepoID(ctx, issue.RepoID, issue.MilestoneID)
 		if err != nil && !IsErrMilestoneNotExist(err) {
 			return fmt.Errorf("getMilestoneByRepoID [repo_id: %d, milestone_id: %d]: %w", issue.RepoID, issue.MilestoneID, err)
 		}
+		issue.isMilestoneLoaded = true
 	}
 	return nil
 }
@@ -327,11 +345,8 @@ func (issue *Issue) LoadAttributes(ctx context.Context) (err error) {
 		return err
 	}
 
-	if issue.Attachments == nil {
-		issue.Attachments, err = repo_model.GetAttachmentsByIssueID(ctx, issue.ID)
-		if err != nil {
-			return fmt.Errorf("getAttachmentsByIssueID [%d]: %w", issue.ID, err)
-		}
+	if err = issue.LoadAttachments(ctx); err != nil {
+		return err
 	}
 
 	if err = issue.loadComments(ctx); err != nil {
@@ -350,6 +365,13 @@ func (issue *Issue) LoadAttributes(ctx context.Context) (err error) {
 	return issue.loadReactions(ctx)
 }
 
+func (issue *Issue) ResetAttributesLoaded() {
+	issue.isLabelsLoaded = false
+	issue.isMilestoneLoaded = false
+	issue.isAttachmentsLoaded = false
+	issue.isAssigneeLoaded = false
+}
+
 // GetIsRead load the `IsRead` field of the issue
 func (issue *Issue) GetIsRead(ctx context.Context, userID int64) error {
 	issueUser := &IssueUser{IssueID: issue.ID, UID: userID}
diff --git a/models/issues/issue_label.go b/models/issues/issue_label.go
index 733f1043b0..10fc821454 100644
--- a/models/issues/issue_label.go
+++ b/models/issues/issue_label.go
@@ -111,6 +111,7 @@ func NewIssueLabel(ctx context.Context, issue *Issue, label *Label, doer *user_m
 		return err
 	}
 
+	issue.isLabelsLoaded = false
 	issue.Labels = nil
 	if err = issue.LoadLabels(ctx); err != nil {
 		return err
@@ -160,6 +161,8 @@ func NewIssueLabels(ctx context.Context, issue *Issue, labels []*Label, doer *us
 		return err
 	}
 
+	// reload all labels
+	issue.isLabelsLoaded = false
 	issue.Labels = nil
 	if err = issue.LoadLabels(ctx); err != nil {
 		return err
@@ -325,11 +328,12 @@ func FixIssueLabelWithOutsideLabels(ctx context.Context) (int64, error) {
 
 // LoadLabels loads labels
 func (issue *Issue) LoadLabels(ctx context.Context) (err error) {
-	if issue.Labels == nil && issue.ID != 0 {
+	if !issue.isLabelsLoaded && issue.Labels == nil && issue.ID != 0 {
 		issue.Labels, err = GetLabelsByIssueID(ctx, issue.ID)
 		if err != nil {
 			return fmt.Errorf("getLabelsByIssueID [%d]: %w", issue.ID, err)
 		}
+		issue.isLabelsLoaded = true
 	}
 	return nil
 }
diff --git a/models/issues/issue_list.go b/models/issues/issue_list.go
index f8ee271a6b..0dd37a04df 100644
--- a/models/issues/issue_list.go
+++ b/models/issues/issue_list.go
@@ -72,18 +72,16 @@ func (issues IssueList) LoadRepositories(ctx context.Context) (repo_model.Reposi
 	return repo_model.ValuesRepository(repoMaps), nil
 }
 
-func (issues IssueList) getPosterIDs() []int64 {
-	return container.FilterSlice(issues, func(issue *Issue) (int64, bool) {
-		return issue.PosterID, true
-	})
-}
-
-func (issues IssueList) loadPosters(ctx context.Context) error {
+func (issues IssueList) LoadPosters(ctx context.Context) error {
 	if len(issues) == 0 {
 		return nil
 	}
 
-	posterMaps, err := getPosters(ctx, issues.getPosterIDs())
+	posterIDs := container.FilterSlice(issues, func(issue *Issue) (int64, bool) {
+		return issue.PosterID, issue.Poster == nil && issue.PosterID > 0
+	})
+
+	posterMaps, err := getPostersByIDs(ctx, posterIDs)
 	if err != nil {
 		return err
 	}
@@ -94,7 +92,7 @@ func (issues IssueList) loadPosters(ctx context.Context) error {
 	return nil
 }
 
-func getPosters(ctx context.Context, posterIDs []int64) (map[int64]*user_model.User, error) {
+func getPostersByIDs(ctx context.Context, posterIDs []int64) (map[int64]*user_model.User, error) {
 	posterMaps := make(map[int64]*user_model.User, len(posterIDs))
 	left := len(posterIDs)
 	for left > 0 {
@@ -136,7 +134,7 @@ func (issues IssueList) getIssueIDs() []int64 {
 	return ids
 }
 
-func (issues IssueList) loadLabels(ctx context.Context) error {
+func (issues IssueList) LoadLabels(ctx context.Context) error {
 	if len(issues) == 0 {
 		return nil
 	}
@@ -168,7 +166,7 @@ func (issues IssueList) loadLabels(ctx context.Context) error {
 			err = rows.Scan(&labelIssue)
 			if err != nil {
 				if err1 := rows.Close(); err1 != nil {
-					return fmt.Errorf("IssueList.loadLabels: Close: %w", err1)
+					return fmt.Errorf("IssueList.LoadLabels: Close: %w", err1)
 				}
 				return err
 			}
@@ -177,7 +175,7 @@ func (issues IssueList) loadLabels(ctx context.Context) error {
 		// When there are no rows left and we try to close it.
 		// Since that is not relevant for us, we can safely ignore it.
 		if err1 := rows.Close(); err1 != nil {
-			return fmt.Errorf("IssueList.loadLabels: Close: %w", err1)
+			return fmt.Errorf("IssueList.LoadLabels: Close: %w", err1)
 		}
 		left -= limit
 		issueIDs = issueIDs[limit:]
@@ -185,6 +183,7 @@ func (issues IssueList) loadLabels(ctx context.Context) error {
 
 	for _, issue := range issues {
 		issue.Labels = issueLabels[issue.ID]
+		issue.isLabelsLoaded = true
 	}
 	return nil
 }
@@ -195,7 +194,7 @@ func (issues IssueList) getMilestoneIDs() []int64 {
 	})
 }
 
-func (issues IssueList) loadMilestones(ctx context.Context) error {
+func (issues IssueList) LoadMilestones(ctx context.Context) error {
 	milestoneIDs := issues.getMilestoneIDs()
 	if len(milestoneIDs) == 0 {
 		return nil
@@ -220,6 +219,7 @@ func (issues IssueList) loadMilestones(ctx context.Context) error {
 
 	for _, issue := range issues {
 		issue.Milestone = milestoneMaps[issue.MilestoneID]
+		issue.isMilestoneLoaded = true
 	}
 	return nil
 }
@@ -263,7 +263,7 @@ func (issues IssueList) LoadProjects(ctx context.Context) error {
 	return nil
 }
 
-func (issues IssueList) loadAssignees(ctx context.Context) error {
+func (issues IssueList) LoadAssignees(ctx context.Context) error {
 	if len(issues) == 0 {
 		return nil
 	}
@@ -310,6 +310,10 @@ func (issues IssueList) loadAssignees(ctx context.Context) error {
 
 	for _, issue := range issues {
 		issue.Assignees = assignees[issue.ID]
+		if len(issue.Assignees) > 0 {
+			issue.Assignee = issue.Assignees[0]
+		}
+		issue.isAssigneeLoaded = true
 	}
 	return nil
 }
@@ -413,6 +417,7 @@ func (issues IssueList) LoadAttachments(ctx context.Context) (err error) {
 
 	for _, issue := range issues {
 		issue.Attachments = attachments[issue.ID]
+		issue.isAttachmentsLoaded = true
 	}
 	return nil
 }
@@ -538,23 +543,23 @@ func (issues IssueList) LoadAttributes(ctx context.Context) error {
 		return fmt.Errorf("issue.loadAttributes: LoadRepositories: %w", err)
 	}
 
-	if err := issues.loadPosters(ctx); err != nil {
-		return fmt.Errorf("issue.loadAttributes: loadPosters: %w", err)
+	if err := issues.LoadPosters(ctx); err != nil {
+		return fmt.Errorf("issue.loadAttributes: LoadPosters: %w", err)
 	}
 
-	if err := issues.loadLabels(ctx); err != nil {
-		return fmt.Errorf("issue.loadAttributes: loadLabels: %w", err)
+	if err := issues.LoadLabels(ctx); err != nil {
+		return fmt.Errorf("issue.loadAttributes: LoadLabels: %w", err)
 	}
 
-	if err := issues.loadMilestones(ctx); err != nil {
-		return fmt.Errorf("issue.loadAttributes: loadMilestones: %w", err)
+	if err := issues.LoadMilestones(ctx); err != nil {
+		return fmt.Errorf("issue.loadAttributes: LoadMilestones: %w", err)
 	}
 
 	if err := issues.LoadProjects(ctx); err != nil {
 		return fmt.Errorf("issue.loadAttributes: loadProjects: %w", err)
 	}
 
-	if err := issues.loadAssignees(ctx); err != nil {
+	if err := issues.LoadAssignees(ctx); err != nil {
 		return fmt.Errorf("issue.loadAttributes: loadAssignees: %w", err)
 	}
 
diff --git a/models/issues/pull.go b/models/issues/pull.go
index 014fcd9fd0..ef49a51045 100644
--- a/models/issues/pull.go
+++ b/models/issues/pull.go
@@ -159,10 +159,11 @@ type PullRequest struct {
 
 	ChangedProtectedFiles []string `xorm:"TEXT JSON"`
 
-	IssueID            int64  `xorm:"INDEX"`
-	Issue              *Issue `xorm:"-"`
-	Index              int64
-	RequestedReviewers []*user_model.User `xorm:"-"`
+	IssueID                    int64  `xorm:"INDEX"`
+	Issue                      *Issue `xorm:"-"`
+	Index                      int64
+	RequestedReviewers         []*user_model.User `xorm:"-"`
+	isRequestedReviewersLoaded bool               `xorm:"-"`
 
 	HeadRepoID          int64                  `xorm:"INDEX"`
 	HeadRepo            *repo_model.Repository `xorm:"-"`
@@ -289,7 +290,7 @@ func (pr *PullRequest) LoadHeadRepo(ctx context.Context) (err error) {
 
 // LoadRequestedReviewers loads the requested reviewers.
 func (pr *PullRequest) LoadRequestedReviewers(ctx context.Context) error {
-	if len(pr.RequestedReviewers) > 0 {
+	if pr.isRequestedReviewersLoaded || len(pr.RequestedReviewers) > 0 {
 		return nil
 	}
 
@@ -297,10 +298,10 @@ func (pr *PullRequest) LoadRequestedReviewers(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-
 	if err = reviews.LoadReviewers(ctx); err != nil {
 		return err
 	}
+	pr.isRequestedReviewersLoaded = true
 	for _, review := range reviews {
 		pr.RequestedReviewers = append(pr.RequestedReviewers, review.Reviewer)
 	}
diff --git a/models/issues/pull_list.go b/models/issues/pull_list.go
index b5557cad06..e8011a916f 100644
--- a/models/issues/pull_list.go
+++ b/models/issues/pull_list.go
@@ -9,8 +9,10 @@ import (
 
 	"code.gitea.io/gitea/models/db"
 	access_model "code.gitea.io/gitea/models/perm/access"
+	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unit"
 	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/container"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/util"
 
@@ -123,7 +125,7 @@ func GetPullRequestIDsByCheckStatus(ctx context.Context, status PullRequestStatu
 }
 
 // PullRequests returns all pull requests for a base Repo by the given conditions
-func PullRequests(ctx context.Context, baseRepoID int64, opts *PullRequestsOptions) ([]*PullRequest, int64, error) {
+func PullRequests(ctx context.Context, baseRepoID int64, opts *PullRequestsOptions) (PullRequestList, int64, error) {
 	if opts.Page <= 0 {
 		opts.Page = 1
 	}
@@ -153,50 +155,93 @@ func PullRequests(ctx context.Context, baseRepoID int64, opts *PullRequestsOptio
 // PullRequestList defines a list of pull requests
 type PullRequestList []*PullRequest
 
+func (prs PullRequestList) getRepositoryIDs() []int64 {
+	repoIDs := make(container.Set[int64])
+	for _, pr := range prs {
+		if pr.BaseRepo == nil && pr.BaseRepoID > 0 {
+			repoIDs.Add(pr.BaseRepoID)
+		}
+		if pr.HeadRepo == nil && pr.HeadRepoID > 0 {
+			repoIDs.Add(pr.HeadRepoID)
+		}
+	}
+	return repoIDs.Values()
+}
+
+func (prs PullRequestList) LoadRepositories(ctx context.Context) error {
+	repoIDs := prs.getRepositoryIDs()
+	reposMap := make(map[int64]*repo_model.Repository, len(repoIDs))
+	if err := db.GetEngine(ctx).
+		In("id", repoIDs).
+		Find(&reposMap); err != nil {
+		return fmt.Errorf("find repos: %w", err)
+	}
+	for _, pr := range prs {
+		if pr.BaseRepo == nil {
+			pr.BaseRepo = reposMap[pr.BaseRepoID]
+		}
+		if pr.HeadRepo == nil {
+			pr.HeadRepo = reposMap[pr.HeadRepoID]
+			pr.isHeadRepoLoaded = true
+		}
+	}
+	return nil
+}
+
 func (prs PullRequestList) LoadAttributes(ctx context.Context) error {
+	if _, err := prs.LoadIssues(ctx); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (prs PullRequestList) LoadIssues(ctx context.Context) (IssueList, error) {
 	if len(prs) == 0 {
-		return nil
+		return nil, nil
 	}
 
 	// Load issues.
 	issueIDs := prs.GetIssueIDs()
-	issues := make([]*Issue, 0, len(issueIDs))
+	issues := make(map[int64]*Issue, len(issueIDs))
 	if err := db.GetEngine(ctx).
-		Where("id > 0").
 		In("id", issueIDs).
 		Find(&issues); err != nil {
-		return fmt.Errorf("find issues: %w", err)
+		return nil, fmt.Errorf("find issues: %w", err)
 	}
 
-	set := make(map[int64]*Issue)
-	for i := range issues {
-		set[issues[i].ID] = issues[i]
-	}
+	issueList := make(IssueList, 0, len(prs))
 	for _, pr := range prs {
-		pr.Issue = set[pr.IssueID]
-		/*
-			Old code:
-			pr.Issue.PullRequest = pr // panic here means issueIDs and prs are not in sync
-
-			It's worth panic because it's almost impossible to happen under normal use.
-			But in integration testing, an asynchronous task could read a database that has been reset.
-			So returning an error would make more sense, let the caller has a choice to ignore it.
-		*/
 		if pr.Issue == nil {
-			return fmt.Errorf("issues and prs may be not in sync: cannot find issue %v for pr %v: %w", pr.IssueID, pr.ID, util.ErrNotExist)
+			pr.Issue = issues[pr.IssueID]
+			/*
+				Old code:
+				pr.Issue.PullRequest = pr // panic here means issueIDs and prs are not in sync
+
+				It's worth panic because it's almost impossible to happen under normal use.
+				But in integration testing, an asynchronous task could read a database that has been reset.
+				So returning an error would make more sense, let the caller has a choice to ignore it.
+			*/
+			if pr.Issue == nil {
+				return nil, fmt.Errorf("issues and prs may be not in sync: cannot find issue %v for pr %v: %w", pr.IssueID, pr.ID, util.ErrNotExist)
+			}
 		}
 		pr.Issue.PullRequest = pr
+		if pr.Issue.Repo == nil {
+			pr.Issue.Repo = pr.BaseRepo
+		}
+		issueList = append(issueList, pr.Issue)
 	}
-	return nil
+	return issueList, nil
 }
 
 // GetIssueIDs returns all issue ids
 func (prs PullRequestList) GetIssueIDs() []int64 {
-	issueIDs := make([]int64, 0, len(prs))
-	for i := range prs {
-		issueIDs = append(issueIDs, prs[i].IssueID)
-	}
-	return issueIDs
+	return container.FilterSlice(prs, func(pr *PullRequest) (int64, bool) {
+		if pr.Issue == nil {
+			return pr.IssueID, pr.IssueID > 0
+		}
+		return 0, false
+	})
 }
 
 // HasMergedPullRequestInRepo returns whether the user(poster) has merged pull-request in the repo
diff --git a/models/user/user.go b/models/user/user.go
index 6848d1be95..23637f4616 100644
--- a/models/user/user.go
+++ b/models/user/user.go
@@ -856,6 +856,10 @@ func GetUserByID(ctx context.Context, id int64) (*User, error) {
 
 // GetUserByIDs returns the user objects by given IDs if exists.
 func GetUserByIDs(ctx context.Context, ids []int64) ([]*User, error) {
+	if len(ids) == 0 {
+		return nil, nil
+	}
+
 	users := make([]*User, 0, len(ids))
 	err := db.GetEngine(ctx).In("id", ids).
 		Table("user").