diff --git a/Directory.Build.props b/Directory.Build.props
index 134b7ea71..733e4e7e8 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -1,6 +1,7 @@
 <Project>
     <PropertyGroup>
         <CSharpLanguageVersion>8</CSharpLanguageVersion>
+        <WarningsAsErrors>0612</WarningsAsErrors>
     </PropertyGroup>
     
     <PropertyGroup>
diff --git a/HwProj.Common/HwProj.Repositories/ReadOnlyRepository.cs b/HwProj.Common/HwProj.Repositories/ReadOnlyRepository.cs
index 4e0b9a4ad..59c94c59e 100644
--- a/HwProj.Common/HwProj.Repositories/ReadOnlyRepository.cs
+++ b/HwProj.Common/HwProj.Repositories/ReadOnlyRepository.cs
@@ -32,7 +32,7 @@ public async Task<TEntity> GetAsync(TKey id)
             return await Context.FindAsync<TEntity>(id).ConfigureAwait(false);
         }
 
-        public async Task<TEntity> FindAsync(Expression<Func<TEntity, bool>> predicate)
+        public virtual async Task<TEntity> FindAsync(Expression<Func<TEntity, bool>> predicate)
         {
             return await Context.Set<TEntity>().AsNoTracking().FirstOrDefaultAsync(predicate).ConfigureAwait(false);
         }
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Domains/MappingExtensions.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Domains/MappingExtensions.cs
index 0393b25f0..bfef52d02 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Domains/MappingExtensions.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Domains/MappingExtensions.cs
@@ -85,7 +85,7 @@ public static CourseDTO ToCourseDto(this Course course)
                 Name = course.Name,
                 GroupName = course.GroupName,
                 IsCompleted = course.IsCompleted,
-                MentorIds = course.MentorIds.Split("/"),
+                MentorIds = course.Mentors.Select(x => x.UserId).ToArray(),
                 IsOpen = course.IsOpen,
                 InviteCode = course.InviteCode,
                 CourseMates = course.CourseMates.Select(cm => cm.ToCourseMateViewModel()).ToArray(),
@@ -99,7 +99,7 @@ public static CoursePreview ToCoursePreview(this Course course)
                 Name = course.Name,
                 GroupName = course.GroupName,
                 IsCompleted = course.IsCompleted,
-                MentorIds = course.MentorIds.Split("/"),
+                MentorIds = course.Mentors.Select(x => x.UserId).ToArray(),
             };
 
         public static HomeworkTask ToHomeworkTask(this CreateTaskViewModel createTaskViewModel)
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Events/LecturerAcceptToCourseEvent.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Events/LecturerAcceptToCourseEvent.cs
index 163af8672..4362ed80f 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Events/LecturerAcceptToCourseEvent.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Events/LecturerAcceptToCourseEvent.cs
@@ -6,7 +6,6 @@ public class LecturerAcceptToCourseEvent : Event
     {
         public long CourseId { get; set; }
         public string CourseName { get; set; }
-        public string MentorIds { get; set; }
         public string StudentId { get; set; }
     }
 }
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Events/LecturerRejectToCourseEvent.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Events/LecturerRejectToCourseEvent.cs
index 9386a6cb1..f6b6fe876 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Events/LecturerRejectToCourseEvent.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Events/LecturerRejectToCourseEvent.cs
@@ -6,7 +6,6 @@ public class LecturerRejectToCourseEvent : Event
     {
         public long CourseId { get; set; }
         public string CourseName { get; set; }
-        public string MentorIds { get; set; }
         public string StudentId { get; set; }
     }
 }
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Events/NewCourseMateEvent.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Events/NewCourseMateEvent.cs
index 747917731..99c1977c9 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Events/NewCourseMateEvent.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Events/NewCourseMateEvent.cs
@@ -6,7 +6,7 @@ public class NewCourseMateEvent : Event
     {
         public long CourseId { get; set; }
         public string CourseName { get; set; }
-        public string MentorIds { get; set; }
+        public string[] MentorIds { get; set; }
         public string StudentId { get; set; }
         public bool IsAccepted { get; set; }
     }
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/20250424012738_'CourseMentors'.Designer.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/20250424012738_'CourseMentors'.Designer.cs
new file mode 100644
index 000000000..16c6dba41
--- /dev/null
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/20250424012738_'CourseMentors'.Designer.cs
@@ -0,0 +1,350 @@
+// <auto-generated />
+using System;
+using HwProj.CoursesService.API.Models;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Metadata;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+
+namespace HwProj.CoursesService.API.Migrations
+{
+    [DbContext(typeof(CourseContext))]
+    [Migration("20250424012738_'CourseMentors'")]
+    partial class CourseMentors
+    {
+        protected override void BuildTargetModel(ModelBuilder modelBuilder)
+        {
+#pragma warning disable 612, 618
+            modelBuilder
+                .HasAnnotation("ProductVersion", "2.2.6-servicing-10079")
+                .HasAnnotation("Relational:MaxIdentifierLength", 128)
+                .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.Assignment", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<long>("CourseId");
+
+                    b.Property<string>("MentorId");
+
+                    b.Property<string>("StudentId");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("CourseId");
+
+                    b.ToTable("Assignments");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.Course", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<string>("GroupName");
+
+                    b.Property<string>("InviteCode");
+
+                    b.Property<bool>("IsCompleted");
+
+                    b.Property<bool>("IsOpen");
+
+                    b.Property<string>("MentorIds");
+
+                    b.Property<string>("Name");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("Courses");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.CourseFilter", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<string>("FilterJson");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("CourseFilters");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.CourseMate", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<long>("CourseId");
+
+                    b.Property<bool>("IsAccepted");
+
+                    b.Property<string>("StudentId");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("CourseId");
+
+                    b.ToTable("CourseMates");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.CourseMentor", b =>
+                {
+                    b.Property<string>("UserId");
+
+                    b.Property<long>("CourseId");
+
+                    b.HasKey("UserId", "CourseId");
+
+                    b.HasIndex("CourseId");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("CourseMentors");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.Group", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<long>("CourseId");
+
+                    b.Property<string>("Name");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("Groups");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.GroupMate", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<long>("GroupId");
+
+                    b.Property<string>("StudentId")
+                        .IsRequired();
+
+                    b.HasKey("Id");
+
+                    b.HasAlternateKey("GroupId", "StudentId");
+
+                    b.ToTable("GroupMates");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.Homework", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<long>("CourseId");
+
+                    b.Property<DateTime?>("DeadlineDate");
+
+                    b.Property<string>("Description");
+
+                    b.Property<bool>("HasDeadline");
+
+                    b.Property<bool>("IsDeadlineStrict");
+
+                    b.Property<DateTime>("PublicationDate");
+
+                    b.Property<string>("Tags");
+
+                    b.Property<string>("Title");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("CourseId");
+
+                    b.ToTable("Homeworks");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.HomeworkTask", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<DateTime?>("DeadlineDate");
+
+                    b.Property<string>("Description");
+
+                    b.Property<bool?>("HasDeadline");
+
+                    b.Property<long>("HomeworkId");
+
+                    b.Property<bool?>("IsDeadlineStrict");
+
+                    b.Property<int>("MaxRating");
+
+                    b.Property<DateTime?>("PublicationDate");
+
+                    b.Property<string>("Title");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("HomeworkId");
+
+                    b.ToTable("Tasks");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.StudentCharacteristics", b =>
+                {
+                    b.Property<long>("CourseMateId");
+
+                    b.Property<string>("Description");
+
+                    b.Property<string>("Tags");
+
+                    b.HasKey("CourseMateId");
+
+                    b.ToTable("StudentCharacteristics");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.TaskModel", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<long>("GroupId");
+
+                    b.Property<long>("TaskId");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("GroupId");
+
+                    b.ToTable("TasksModels");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.TaskQuestion", b =>
+                {
+                    b.Property<long>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
+
+                    b.Property<string>("Answer")
+                        .HasMaxLength(1000);
+
+                    b.Property<bool>("IsPrivate");
+
+                    b.Property<string>("LecturerId");
+
+                    b.Property<string>("StudentId");
+
+                    b.Property<long>("TaskId");
+
+                    b.Property<string>("Text")
+                        .HasMaxLength(1000);
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("TaskId");
+
+                    b.ToTable("Questions");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.UserToCourseFilter", b =>
+                {
+                    b.Property<long>("CourseId");
+
+                    b.Property<string>("UserId");
+
+                    b.Property<long>("CourseFilterId");
+
+                    b.HasKey("CourseId", "UserId");
+
+                    b.HasIndex("CourseFilterId");
+
+                    b.ToTable("UserToCourseFilters");
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.Assignment", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.Course")
+                        .WithMany("Assignments")
+                        .HasForeignKey("CourseId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.CourseMate", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.Course")
+                        .WithMany("CourseMates")
+                        .HasForeignKey("CourseId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.CourseMentor", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.Course")
+                        .WithMany("Mentors")
+                        .HasForeignKey("CourseId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.GroupMate", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.Group")
+                        .WithMany("GroupMates")
+                        .HasForeignKey("GroupId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.Homework", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.Course")
+                        .WithMany("Homeworks")
+                        .HasForeignKey("CourseId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.HomeworkTask", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.Homework", "Homework")
+                        .WithMany("Tasks")
+                        .HasForeignKey("HomeworkId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.StudentCharacteristics", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.CourseMate")
+                        .WithOne("Characteristics")
+                        .HasForeignKey("HwProj.CoursesService.API.Models.StudentCharacteristics", "CourseMateId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.TaskModel", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.Group")
+                        .WithMany("Tasks")
+                        .HasForeignKey("GroupId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.UserToCourseFilter", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.CourseFilter", "CourseFilter")
+                        .WithMany()
+                        .HasForeignKey("CourseFilterId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+#pragma warning restore 612, 618
+        }
+    }
+}
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/20250424012738_'CourseMentors'.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/20250424012738_'CourseMentors'.cs
new file mode 100644
index 000000000..3aaade4d9
--- /dev/null
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/20250424012738_'CourseMentors'.cs
@@ -0,0 +1,63 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+namespace HwProj.CoursesService.API.Migrations
+{
+    public partial class CourseMentors : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "CourseMentors",
+                columns: table => new
+                {
+                    UserId = table.Column<string>(nullable: false),
+                    CourseId = table.Column<long>(nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_CourseMentors", x => new { x.UserId, x.CourseId });
+                    table.ForeignKey(
+                        name: "FK_CourseMentors_Courses_CourseId",
+                        column: x => x.CourseId,
+                        principalTable: "Courses",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Cascade);
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "IX_CourseMentors_CourseId",
+                table: "CourseMentors",
+                column: "CourseId");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_CourseMentors_UserId",
+                table: "CourseMentors",
+                column: "UserId");
+
+            // Миграция данных: Перенос MentorIds в таблицу CourseMentor
+            // language=SQL
+            migrationBuilder.Sql(@"
+-- Разделим MentorIds на элементы, преобразуем в строки, удалим дубликаты и вставим в таблицу CourseMentor
+WITH SplitMentorIds AS (
+    SELECT
+        c.Id AS CourseId,
+        LTRIM(RTRIM(value)) AS MentorId
+    FROM Courses c
+    CROSS APPLY STRING_SPLIT(c.MentorIds, '/') -- Разделяем MentorIds по запятой
+)
+, DistinctMentors AS (
+    SELECT DISTINCT
+        MentorId,
+        CourseId
+    FROM SplitMentorIds
+    WHERE MentorId <> '' -- Исключаем пустые строки
+)
+INSERT INTO CourseMentors (UserId, CourseId)
+SELECT
+    MentorId,
+    CourseId
+FROM DistinctMentors;
+");
+        }
+    }
+}
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/CourseContextModelSnapshot.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/CourseContextModelSnapshot.cs
index 736fb0058..26fc00997 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/CourseContextModelSnapshot.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Migrations/CourseContextModelSnapshot.cs
@@ -93,6 +93,21 @@ protected override void BuildModel(ModelBuilder modelBuilder)
                     b.ToTable("CourseMates");
                 });
 
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.CourseMentor", b =>
+                {
+                    b.Property<string>("UserId");
+
+                    b.Property<long>("CourseId");
+
+                    b.HasKey("UserId", "CourseId");
+
+                    b.HasIndex("CourseId");
+
+                    b.HasIndex("UserId");
+
+                    b.ToTable("CourseMentors");
+                });
+
             modelBuilder.Entity("HwProj.CoursesService.API.Models.Group", b =>
                 {
                     b.Property<long>("Id")
@@ -272,6 +287,14 @@ protected override void BuildModel(ModelBuilder modelBuilder)
                         .OnDelete(DeleteBehavior.Cascade);
                 });
 
+            modelBuilder.Entity("HwProj.CoursesService.API.Models.CourseMentor", b =>
+                {
+                    b.HasOne("HwProj.CoursesService.API.Models.Course")
+                        .WithMany("Mentors")
+                        .HasForeignKey("CourseId")
+                        .OnDelete(DeleteBehavior.Cascade);
+                });
+
             modelBuilder.Entity("HwProj.CoursesService.API.Models.GroupMate", b =>
                 {
                     b.HasOne("HwProj.CoursesService.API.Models.Group")
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Models/Course.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Models/Course.cs
index e5f6af8a3..3efb5b4e9 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Models/Course.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Models/Course.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using HwProj.Repositories;
 
@@ -12,7 +13,8 @@ public class Course : IEntity<long>
         public bool IsOpen { get; set; }
         public string InviteCode { get; set; }
         public bool IsCompleted { get; set; }
-        public string MentorIds { get; set; }
+        [Obsolete] public string MentorIds { get; set; }
+        public List<CourseMentor> Mentors { get; set; } = new List<CourseMentor>();
         public List<CourseMate> CourseMates { get; set; } = new List<CourseMate>();
         public List<Homework> Homeworks { get; set; } = new List<Homework>();
         public List<Assignment> Assignments { get; set; } = new List<Assignment>();
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Models/CourseContext.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Models/CourseContext.cs
index ca089ff93..ebd5e1fe5 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Models/CourseContext.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Models/CourseContext.cs
@@ -5,6 +5,7 @@ namespace HwProj.CoursesService.API.Models
     public sealed class CourseContext : DbContext
     {
         public DbSet<Course> Courses { get; set; }
+        public DbSet<CourseMentor> CourseMentors { get; set; }
         public DbSet<CourseMate> CourseMates { get; set; }
         public DbSet<Group> Groups { get; set; }
         public DbSet<GroupMate> GroupMates { get; set; }
@@ -27,6 +28,10 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
             modelBuilder.Entity<Assignment>().HasIndex(a => a.CourseId);
             modelBuilder.Entity<UserToCourseFilter>().HasKey(u => new { u.CourseId, u.UserId });
             modelBuilder.Entity<TaskQuestion>().HasIndex(t => t.TaskId);
+
+            modelBuilder.Entity<CourseMentor>().HasKey(m => new { m.UserId, m.CourseId });
+            modelBuilder.Entity<CourseMentor>().HasIndex(m => m.UserId);
+            modelBuilder.Entity<CourseMentor>().HasIndex(m => m.CourseId);
         }
     }
 }
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Models/CourseMentor.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Models/CourseMentor.cs
new file mode 100644
index 000000000..8fa0abdcf
--- /dev/null
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Models/CourseMentor.cs
@@ -0,0 +1,11 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace HwProj.CoursesService.API.Models
+{
+    [Table("CourseMentors")]
+    public class CourseMentor
+    {
+        public string UserId { get; set; }
+        public long CourseId { get; set; }
+    }
+}
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Repositories/CoursesRepository.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Repositories/CoursesRepository.cs
index 17e4bd829..09254f343 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Repositories/CoursesRepository.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Repositories/CoursesRepository.cs
@@ -1,4 +1,6 @@
-using System.Linq;
+using System;
+using System.Linq;
+using System.Linq.Expressions;
 using System.Threading.Tasks;
 using HwProj.CoursesService.API.Models;
 using HwProj.Repositories;
@@ -6,6 +8,7 @@
 
 namespace HwProj.CoursesService.API.Repositories
 {
+    // TODO: include mentors by default
     public class CoursesRepository : CrudRepository<Course, long>, ICoursesRepository
     {
         public CoursesRepository(CourseContext context)
@@ -13,8 +16,14 @@ public CoursesRepository(CourseContext context)
         {
         }
 
+        public override async Task<Course> FindAsync(Expression<Func<Course, bool>> predicate)
+        {
+            return await Context.Set<Course>().AsNoTracking().Include(x => x.Mentors).FirstOrDefaultAsync(predicate);
+        }
+
         public Task<Course?> GetWithCourseMates(long id) =>
             Context.Set<Course>()
+                .Include(x => x.Mentors)
                 .Include(c => c.CourseMates)
                 .ThenInclude(c => c.Characteristics)
                 .AsNoTracking()
@@ -22,6 +31,7 @@ public CoursesRepository(CourseContext context)
 
         public async Task<Course?> GetWithHomeworksAsync(long id)
             => await Context.Set<Course>()
+                .Include(x => x.Mentors)
                 .Include(c => c.Homeworks)
                 .ThenInclude(h => h.Tasks)
                 .AsNoTracking()
@@ -30,6 +40,7 @@ public CoursesRepository(CourseContext context)
         public async Task<Course?> GetWithCourseMatesAndHomeworksAsync(long id)
         {
             var course = await Context.Set<Course>()
+                .Include(x => x.Mentors)
                 .Include(c => c.CourseMates)
                 .ThenInclude(c => c.Characteristics)
                 .Include(c => c.Homeworks)
@@ -45,6 +56,7 @@ public CoursesRepository(CourseContext context)
         public IQueryable<Course> GetAllWithCourseMatesAndHomeworks()
         {
             return Context.Set<Course>()
+                .Include(x => x.Mentors)
                 .Include(c => c.CourseMates)
                 .ThenInclude(c => c.Characteristics)
                 .Include(c => c.Homeworks)
diff --git a/HwProj.CoursesService/HwProj.CoursesService.API/Services/CoursesService.cs b/HwProj.CoursesService/HwProj.CoursesService.API/Services/CoursesService.cs
index 7fd03cdb0..141990b80 100644
--- a/HwProj.CoursesService/HwProj.CoursesService.API/Services/CoursesService.cs
+++ b/HwProj.CoursesService/HwProj.CoursesService.API/Services/CoursesService.cs
@@ -113,8 +113,8 @@ public async Task<long> AddFromTemplateAsync(CourseTemplate courseTemplate, List
             using var transactionScope = new TransactionScope(TransactionScopeAsyncFlowOption.Enabled);
 
             var course = courseTemplate.ToCourse();
-            course.MentorIds = mentorId;
             course.InviteCode = Guid.NewGuid().ToString();
+            course.Mentors = new List<CourseMentor> { new CourseMentor { UserId = mentorId } };
             var courseId = await _coursesRepository.AddAsync(course);
 
             var homeworks = courseTemplate.Homeworks.Select(hwTemplate => hwTemplate.ToHomework(courseId));
@@ -141,7 +141,6 @@ public async Task<long> AddFromTemplateAsync(CourseTemplate courseTemplate, List
                     {
                         CourseId = courseId,
                         CourseName = course.Name,
-                        MentorIds = course.MentorIds,
                         StudentId = student.StudentId
                     });
                 }
@@ -187,7 +186,7 @@ public async Task<bool> AddStudentAsync(long courseId, string studentId)
             {
                 CourseId = courseId,
                 CourseName = course.Name,
-                MentorIds = course.MentorIds,
+                MentorIds = course.Mentors.Select(x => x.UserId).ToArray(),
                 StudentId = studentId,
                 IsAccepted = false
             });
@@ -209,7 +208,6 @@ public async Task<bool> AcceptCourseMateAsync(long courseId, string studentId)
             {
                 CourseId = courseId,
                 CourseName = course.Name,
-                MentorIds = course.MentorIds,
                 StudentId = studentId
             });
 
@@ -230,7 +228,6 @@ public async Task<bool> RejectCourseMateAsync(long courseId, string studentId)
             {
                 CourseId = courseId,
                 CourseName = course.Name,
-                MentorIds = course.MentorIds,
                 StudentId = studentId
             });
             return true;
@@ -241,10 +238,11 @@ public async Task<CourseDTO[]> GetUserCoursesAsync(string userId, string role)
             var isMentor = role == Roles.LecturerRole || role == Roles.ExpertRole;
 
             var courses = isMentor
-                ? _coursesRepository.FindAll(c => c.MentorIds.Contains(userId))
+                ? _coursesRepository.FindAll(c => c.Mentors.Any(m => m.UserId == userId))
                 : _coursesRepository.FindAll(c => c.CourseMates.Any(cm => cm.IsAccepted && cm.StudentId == userId));
 
             var coursesWithValues = await courses
+                .Include(c => c.Mentors)
                 .Include(c => c.CourseMates)
                 .Include(c => c.Homeworks).ThenInclude(t => t.Tasks)
                 .ToArrayAsync();
@@ -271,13 +269,10 @@ public async Task<bool> AcceptLecturerAsync(long courseId, string lecturerEmail,
         {
             var course = await _coursesRepository.GetAsync(courseId);
             if (course == null) return false;
-            if (!course.MentorIds.Contains(lecturerId))
+            if (course.Mentors.All(x => x.UserId != lecturerId))
             {
-                var newMentors = course.MentorIds + "/" + lecturerId;
-                await _coursesRepository.UpdateAsync(courseId, с => new Course
-                {
-                    MentorIds = newMentors,
-                });
+                await _context.CourseMentors.AddAsync(new CourseMentor() { CourseId = courseId, UserId = lecturerId });
+                await _context.SaveChangesAsync();
 
                 _eventBus.Publish(new LecturerInvitedToCourseEvent
                 {
@@ -286,8 +281,6 @@ public async Task<bool> AcceptLecturerAsync(long courseId, string lecturerEmail,
                     MentorId = lecturerId,
                     MentorEmail = lecturerEmail
                 });
-                //TODO: remove
-                await RejectCourseMateAsync(courseId, lecturerId);
             }
 
             return true;
@@ -296,7 +289,7 @@ public async Task<bool> AcceptLecturerAsync(long courseId, string lecturerEmail,
         public async Task<string[]> GetCourseLecturers(long courseId)
         {
             var course = await _coursesRepository.GetAsync(courseId);
-            return course.MentorIds.Split('/');
+            return course.Mentors.Select(x => x.UserId).ToArray();
         }
 
         public async Task<bool> HasStudent(long courseId, string studentId)
diff --git a/HwProj.NotificationsService/HwProj.NotificationsService.API/EventHandlers/NewCourseMateHandler.cs b/HwProj.NotificationsService/HwProj.NotificationsService.API/EventHandlers/NewCourseMateHandler.cs
index eab810b0f..f3f755d44 100644
--- a/HwProj.NotificationsService/HwProj.NotificationsService.API/EventHandlers/NewCourseMateHandler.cs
+++ b/HwProj.NotificationsService/HwProj.NotificationsService.API/EventHandlers/NewCourseMateHandler.cs
@@ -38,7 +38,7 @@ public override async Task HandleAsync(NewCourseMateEvent @event)
             var user = await _authServiceClient.GetAccountData(@event.StudentId);
             var url = _configuration["Url"];
 
-            var mentorIds = @event.MentorIds.Split('/');
+            var mentorIds = @event.MentorIds;
             var mentors = await _authServiceClient.GetAccountsData(mentorIds);
 
             //TODO: fix