游标分页优化

src/Jiaowu.Api/Controllers/TeachingTasksController.cs

@@ -30,8 +30,8 @@ public sealed class TeachingTasksController(
         SystemRoles.AcademicAdmin;
 
     [HttpGet]
-    public async Task<ActionResult<PagedResult<object>>> Get(
-        int page = 1,
+    public async Task<ActionResult<CursorPagedResult<object>>> Get(
+        string? cursor = null,
         int pageSize = 20,
         string? keyword = null,
         Guid? academicTermId = null,
@@ -41,8 +41,9 @@ public sealed class TeachingTasksController(
         string? teacherKeyword = null,
         string? classKeyword = null)
     {
-        page = Math.Max(1, page);
         pageSize = Math.Clamp(pageSize, 10, 100);
+        if (!CursorToken.TryDecode<TaskCursor>(cursor, out var after))
+            return BadRequest("教学任务游标无效。");
         var source = ScopedTasks().AsNoTracking();
         if (academicTermId.HasValue)
             source = source.Where(x => x.AcademicTermId == academicTermId);
@@ -75,11 +76,18 @@ public sealed class TeachingTasksController(
         }
 
         var total = await source.CountAsync(cancellationToken);
-        var items = await source
+        if (after is not null)
+        {
+            source = source.Where(x => x.AcademicTerm!.StartDate < after.TermStartDate ||
+                x.AcademicTerm.StartDate == after.TermStartDate &&
+                (x.TaskNumber.CompareTo(after.TaskNumber) > 0 ||
+                 x.TaskNumber == after.TaskNumber && x.Id.CompareTo(after.Id) > 0));
+        }
+        var rows = await source
             .OrderByDescending(x => x.AcademicTerm!.StartDate)
             .ThenBy(x => x.TaskNumber)
-            .Skip((page - 1) * pageSize)
-            .Take(pageSize)
+            .ThenBy(x => x.Id)
+            .Take(pageSize + 1)
             .Select(x => new
             {
                 x.Id,
@@ -87,6 +95,7 @@ public sealed class TeachingTasksController(
                 x.Name,
                 x.AcademicTermId,
                 TermName = x.AcademicTerm!.Name,
+                TermStartDate = x.AcademicTerm.StartDate,
                 x.CourseId,
                 CourseCode = x.Course!.Code,
                 CourseName = x.Course.Name,
@@ -114,9 +123,17 @@ public sealed class TeachingTasksController(
                 x.UpdatedAt
             })
             .ToListAsync(cancellationToken);
-        return Ok(new PagedResult<object>(items, total, page, pageSize));
+        var hasMore = rows.Count > pageSize;
+        var items = rows.Take(pageSize).ToArray();
+        var last = items.LastOrDefault();
+        return Ok(new CursorPagedResult<object>(items.Cast<object>().ToArray(),
+            hasMore && last is not null
+                ? CursorToken.Encode(new TaskCursor(last.TermStartDate, last.TaskNumber, last.Id)) : null,
+            hasMore, pageSize, total));
     }
 
+    private sealed record TaskCursor(DateOnly TermStartDate, string TaskNumber, Guid Id);
+
     [HttpGet("options")]
     public async Task<ActionResult> GetOptions(
         Guid academicTermId,