Use batch database operations instead of one by one to optimze api pulls (#32680)

Resolve #31492

The response time for the Pull Requests API has improved significantly,
dropping from over `2000ms` to about `350ms` on my local machine. It's
about `6` times faster.

A key area for further optimization lies in batch-fetching data for
`apiPullRequest.ChangedFiles, apiPullRequest.Additions, and
apiPullRequest.Deletions`.

Tests `TestAPIViewPulls` does exist and new tests added.

- This PR also fixes some bugs in `GetDiff` functions.
- This PR also fixes data inconsistent in test data. For a pull request,
the head branch's reference should be equal to the reference in
`pull/xxx/head`.

models/issues/pull_list.go

@@ -16,6 +16,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/util"
 
+	"xorm.io/builder"
 	"xorm.io/xorm"
 )
 
@@ -240,6 +241,64 @@ func (prs PullRequestList) GetIssueIDs() []int64 {
 	})
 }
 
+func (prs PullRequestList) LoadReviewCommentsCounts(ctx context.Context) (map[int64]int, error) {
+	issueIDs := prs.GetIssueIDs()
+	countsMap := make(map[int64]int, len(issueIDs))
+	counts := make([]struct {
+		IssueID int64
+		Count   int
+	}, 0, len(issueIDs))
+	if err := db.GetEngine(ctx).Select("issue_id, count(*) as count").
+		Table("comment").In("issue_id", issueIDs).And("type = ?", CommentTypeReview).
+		GroupBy("issue_id").Find(&counts); err != nil {
+		return nil, err
+	}
+	for _, c := range counts {
+		countsMap[c.IssueID] = c.Count
+	}
+	return countsMap, nil
+}
+
+func (prs PullRequestList) LoadReviews(ctx context.Context) (ReviewList, error) {
+	issueIDs := prs.GetIssueIDs()
+	reviews := make([]*Review, 0, len(issueIDs))
+
+	subQuery := builder.Select("max(id) as id").
+		From("review").
+		Where(builder.In("issue_id", issueIDs)).
+		And(builder.In("`type`", ReviewTypeApprove, ReviewTypeReject, ReviewTypeRequest)).
+		And(builder.Eq{
+			"dismissed":          false,
+			"original_author_id": 0,
+			"reviewer_team_id":   0,
+		}).
+		GroupBy("issue_id, reviewer_id")
+	// Get latest review of each reviewer, sorted in order they were made
+	if err := db.GetEngine(ctx).In("id", subQuery).OrderBy("review.updated_unix ASC").Find(&reviews); err != nil {
+		return nil, err
+	}
+
+	teamReviewRequests := make([]*Review, 0, 5)
+	subQueryTeam := builder.Select("max(id) as id").
+		From("review").
+		Where(builder.In("issue_id", issueIDs)).
+		And(builder.Eq{
+			"original_author_id": 0,
+		}).And(builder.Neq{
+		"reviewer_team_id": 0,
+	}).
+		GroupBy("issue_id, reviewer_team_id")
+	if err := db.GetEngine(ctx).In("id", subQueryTeam).OrderBy("review.updated_unix ASC").Find(&teamReviewRequests); err != nil {
+		return nil, err
+	}
+
+	if len(teamReviewRequests) > 0 {
+		reviews = append(reviews, teamReviewRequests...)
+	}
+
+	return reviews, nil
+}
+
 // HasMergedPullRequestInRepo returns whether the user(poster) has merged pull-request in the repo
 func HasMergedPullRequestInRepo(ctx context.Context, repoID, posterID int64) (bool, error) {
 	return db.GetEngine(ctx).