Implement IAssignedGradesService.GetAssignerIdAsync

Core/Services/University/Grades/IAssignedGradesService.cs

@@ -5,6 +5,13 @@
 
 namespace EUniversity.Core.Services.University.Grades;
 
+/// <summary>
+/// Response of the <see cref="IGroupsService.GetAssignerIdAsync(int)" /> method.
+/// </summary>
+/// <param name="GradeExists">Flag that determines whether requested assigned grade exists.</param>
+/// <param name="AssignerId">ID of the assigner of the grade.</param>
+public record GetAssignerIdResponse(bool GradeExists, string? AssignerId);
+
 /// <summary>
 /// An interface for retrieving and assigning grades.
 /// </summary>
@@ -66,4 +73,14 @@ Task<Page<TViewDto>> GetPageAsync<TViewDto>(PaginationProperties properties, IFi
     /// it returns <see langword="false" />.
     /// </returns>
     Task<bool> DeleteAsync(int id);
+
+    /// <summary>
+    /// Gets an ID of the assigner of the assigned grade.
+    /// </summary>
+    /// <param name="id">ID of the assigned grade.</param>
+    /// <returns>
+    /// A task that represent the asynchronous operation and the result
+    /// of the operation.
+    /// </returns>
+    Task<GetAssignerIdResponse> GetAssignerIdAsync(int id);
 }

Infrastructure/Services/University/Grades/AssignedGradesService.cs

@@ -102,4 +102,18 @@ public async Task<bool> DeleteAsync(int id)
 
         return true;
     }
+
+    /// <inheritdoc />
+    public async Task<GetAssignerIdResponse> GetAssignerIdAsync(int id)
+    {
+        var grade = await _dbContext.AssignedGrades
+            .AsNoTracking()
+            .Where(g => g.Id == id)
+            .FirstOrDefaultAsync();
+        if (grade == null)
+        {
+            return new(false, null);
+        }
+        return new(true, grade.AssignerId);
+    }
 }

IntegrationTests/Services/University/Grades/AssignedGradesServiceTests.cs

@@ -249,4 +249,35 @@ public async Task Delete_ElementDoesNotExist_ReturnsFalse()
         // Assert
         Assert.That(result, Is.False);
     }
+
+    [Test]
+    public async Task GetAssignerId_GradeExists_ReturnsGroupOwner()
+    {
+        // Arrange
+        var grade = await CreateTestAssignedGradeAsync();
+
+        // Act
+        var result = await _service.GetAssignerIdAsync(grade.Id);
+
+        // Assert
+        Assert.Multiple(() =>
+        {
+            Assert.That(result.GradeExists, Is.True);
+            Assert.That(result.AssignerId, Is.EqualTo(grade.AssignerId));
+        });
+    }
+
+    [Test]
+    public async Task GetAssignerId_GradeDoesNotExist_ReturnsCorrectResponse()
+    {
+        // Act
+        var result = await _service.GetAssignerIdAsync(-1);
+
+        // Assert
+        Assert.Multiple(() =>
+        {
+            Assert.That(result.GradeExists, Is.False);
+            Assert.That(result.AssignerId, Is.Null);
+        });
+    }
 }