title: CollectionNavigationBuilder does not contain a definition for .WithMany
body: <p>I am using .NET 3.1.21 and I'm getting the error:</p>
  <blockquote>
  <p>'CollectionNavigationBuilder&lt;ApplicationUser, ClassroomGroup&gt;' does not contain a definition for 'WithMany' and no accessible extension method 'WithMany' accepting a first argument of type 'CollectionNavigationBuilder&lt;ApplicationUser, ClassroomGroup&gt;' could be found (are you missing a using directive or an assembly reference?)</p>
  </blockquote>
  <p>The syntax seems to be okay from what I've seen so far.</p>
  <p>ApplicationDbContext</p>
  <pre class="lang-cs prettyprint-override"><code>protected override void OnModelCreating(ModelBuilder builder)
          {
              base.OnModelCreating(builder);
  
              foreach (var relationship in builder.Model.GetEntityTypes().SelectMany(e =&gt; e.GetForeignKeys()))
                  relationship.DeleteBehavior = DeleteBehavior.Restrict;
  
              builder.Entity&lt;ApplicationUser&gt;().HasMany(x =&gt; x.TeacherGroups).WithOne(x =&gt; x.Teacher).OnDelete(DeleteBehavior.SetNull);
              builder.Entity&lt;ApplicationUser&gt;().HasMany(x =&gt; x.StudentGroups).WithMany(x =&gt; x.Students); //this .WithMany gives me the error
  
  builder.Entity&lt;ApplicationUser&gt;().HasMany(x =&gt; x.UserRoles).WithOne(x =&gt; x.User)
                  .HasForeignKey(x =&gt; x.UserId).IsRequired().OnDelete(DeleteBehavior.Cascade);
          }
  </code></pre>
  <p>ApplicationUser</p>
  <pre class="lang-cs prettyprint-override"><code>public class ApplicationUser : IdentityUser
      {
          public virtual ICollection&lt;ApplicationUserRole&gt; UserRoles { get; set; }
          public virtual ICollection&lt;ClassroomGroup&gt; TeacherGroups { get; set; }
          public virtual ICollection&lt;ClassroomGroup&gt; StudentGroups { get; set; }
          public virtual ICollection&lt;Task&gt; CreatedTasks { get; set; }
          public virtual ICollection&lt;SchoolClassStudentTerm&gt; SchoolClassStudentTerms { get; set; }
          public virtual ICollection&lt;GroupAssignment&gt; CreatedGroupAssignments { get; set; }
          public bool Disabled { get; set; }
          public String FullName { get; set; }
          public DateTime? StartTime { get; set; }
      }
  </code></pre>
  <p>ClassroomGroup</p>
  <pre class="lang-cs prettyprint-override"><code>public class ClassroomGroup
      {
          public int SubjectId { get; set; }
          public virtual Subject Subject { get; set; }
          public virtual SchoolClass SchoolClass { get; set; }
          public int SchoolClassId { get; set; }
          public String TeacherId { get; set; }
          public virtual ApplicationUser Teacher { get; set; }
          public int Id { get; set; }
          public String Title { get; set; }
          public virtual ICollection&lt;ApplicationUser&gt; Students { get; set; }
          public int TermId { get; set; }
          public virtual Term Term { get; set; }
          public virtual ICollection&lt;GroupAssignment&gt; GroupAssignments { get; set; }
      }
  </code></pre>
  <p>All packages are up to date</p>