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Recursive query takes too much time to load data in C#

*I have written a recursive query to get unlimited menu layer. The query works fine providing the exact results but it takes too much time to load. It takes probably 10 to 15 seconds. Please help me if I need to do anything to improve the performance. I have provided all the code to find out the problem. for mapping from entity to view model I have used automapper. *
Entity:
public class Menus
{
public int Id { get; set; }
public string Icon { get; set; }
public string Label { get; set; }
public string To { get; set; }
[ForeignKey("Parents")]
public int? ParentsId { get; set; }
public string Key { get; set; }
public bool? Permitted { get; set; }
public Menus Parents { get; set; }
public ICollection<Menus> Subs { get; set; }
public ICollection<MenusRole> MenusRoles { get; set; }
}
Query:
public async Task<IEnumerable<Menus>> GetAllMenusAsync()
{
List<Menus> temp = await ApplicationDbContext
.Menus
.Include(x => x.Subs)
.Where(x => x.Parents == null)
.Select(f => new Menus
{
Id = f.Id,
Key = f.Key,
Label = f.Label,
To = f.To,
Icon = f.Icon,
ParentsId = f.ParentsId,
Subs = f.Subs
}).ToListAsync();
return Get_all_menus(temp);
}
public List<Menus> Get_all_menus(List<Menus> menus)
{
int z = 0;
List<Menus> menuList = new List<Menus>();
if (menus.Count > 0)
{
menuList.AddRange(menus);
}
foreach (Menus item in menus)
{
Menus menu = ApplicationDbContext
.Menus
.Include(y => y.Subs)
.Where(y => y.Id == item.Id)
.Select(y => new Menus
{
Id = y.Id,
Key = y.Key,
Label = y.Label,
To = y.To,
Icon = y.Icon,
ParentsId = y.ParentsId,
Subs = y.Subs,
Permitted = true
}).First();
if (menu.Subs == null)
{
z++;
continue;
}
List<Menus> subMenu = menu.Subs.ToList();
menu.Subs = Get_all_menus(subMenu);
menuList[z] = menu;
z++;
}
return menuList;
}
In Controller
[HttpGet("get-all-menus")]
public async Task<ActionResult> GetAllMenus()
{
var menus = await _menusService.GetAllMenus();
var menusResources = _mapper.Map<IEnumerable<Menus>, IEnumerable<MenusResourceForSidebar>>(menus);
return Ok(menusResources);
}
View Model
public string Id { get; set; }
public string Icon { get; set; }
public string Label { get; set; }
public string To { get; set; }
public bool? Permitted { get; set; }
public ICollection<MenusResourceForSidebar> Subs { get; set; }

Instead of loading the root menus, then loading the children in separate queries, just load the whole collection in one query, and then populate the navigation links afterwards.
public async Task<IEnumerable<Menus>> GetAllMenusAsync()
{
List<Menus> temp = await ApplicationDbContext.Menus.ToList();
List<Menus> topLevel = new List<Menu>();
foreach (var menu in temp)
{
if (menu.ParentsId == null)
{
topLevel.Add(menu);
continue;
}
var parent = temp.Find(x => x.Id == temp.ParentsId.Value);
if (parent.Subs == null)
parent.Subs = new List<Menus>();
parent.Subs.Add(menu);
}
return topLevel;
}

You should just be able to do:
context.Menus.Include(m => m.Subs).ToList();
The relationship fixup in EFCore will link all the menus together in a tree for you. In later EFs you don't even need the Include..
context.Menus.ToList();
Here is a table in SSMS:
Here is the data:
Here it is chopped up in a paint program and rearranged into a tree:
Here's the scaffolded entity:
// <auto-generated> This file has been auto generated by EF Core Power Tools. </auto-generated>
#nullable disable
using System.Collections.Generic;
namespace ConsoleApp7net5.Models
{
public partial class Menu
{
public Menu()
{
InverseParent = new HashSet<Menu>();
}
public int Id { get; set; }
public int? ParentId { get; set; }
public string Label { get; set; }
public virtual Menu Parent { get; set; }
public virtual ICollection<Menu> InverseParent { get; set; }
}
}
Here's what we see after asking EFC (5, in my case) to download it all with just a ToList:
Of course it might make sense to start with a root (or multiple roots but my data only has one)
Don't give classes plural names (Menus), btw, and don't give properties plural names if they aren't collections/enumerables (Parents) - it makes for very confusing code

Get objects whose property does not exist in enumerable

Multiple answers have led me to the following 2 solutions, but both of them do not seem to be working correctly.
What I have are 2 objects
public class DatabaseAssignment : AuditableEntity
{
public Guid Id { get; set; }
public string User_Id { get; set; }
public Guid Database_Id { get; set; }
}
public class Database : AuditableEntity
{
public Guid Id { get; set; }
public string Name { get; set; }
public string Server { get; set; }
public bool IsActive { get; set; }
public Guid DatabaseClientId { get; set; }
}
Now, the front-end will return all selected Database objects (as IEnumerable) for a given user. I am grabbing all current DatabaseAssignments from the database for the given user and comparing them to the databases by the Database.ID property. My goal is to find the DatabaseAssignments that I can remove from the database. However, my solutions keep returning all DatabaseAssignments to be removed.
if (databases != null)
{
var unitOfWork = new UnitOfWork(_context);
var userDatabaseAssignments = unitOfWork.DatabaseAssignments.GetAll().Where(d => d.User_Id == user.Id);
//var assignmentsToRemove = userDatabaseAssignments.Where(ud => databases.Any(d => d.Id != ud.Database_Id));
var assignmentsToRemove = userDatabaseAssignments.Select(ud => userDatabaseAssignments.FirstOrDefault()).Where(d1 => databases.All(d2 => d2.Id != d1.Database_Id));
var assignmentsToAdd = databases.Select(d => new DatabaseAssignment { User_Id = user.Id, Database_Id = d.Id }).Where(ar => assignmentsToRemove.All(a => a.Database_Id != ar.Database_Id));
if (assignmentsToRemove.Any())
{
unitOfWork.DatabaseAssignments.RemoveRange(assignmentsToRemove);
}
if (assignmentsToAdd.Any())
{
unitOfWork.DatabaseAssignments.AddRange(assignmentsToAdd);
}
unitOfWork.SaveChanges();
}

I think u are looking for an Except extension, have a look at this link
LINQ: Select where object does not contain items from list
Or other way is with contains see below Fiddler link :
https://dotnetfiddle.net/lKyI2F

Sequence contains more than one element when using Contains in LINQ query

The following code is throwing an InvalidOperationException: Sequence contains more than one element. The errors occurs whether I have the Include statement or not.
long[] customerIDs; //Method parameter. Has valid values
var results = from x in DB.CycleCounts
//.Include(y => y.CustomerInventoryItem)
select x;
if (customerIDs != null && customerIDs.Length > 0)
{
results = from x in results
where customerIDs.Contains(x.CustomerInventoryItem.CustomerID)
select x;
}
var cycleCounts = await results.ToListAsync(); //throws InvalidOperationException
I am using ASP5 RC1 (Core), and Entity Framework 7

I not sure how look your models, but I think that they looks like something below (relationship between CycleCounts and CustomerInventoryItems as many-to-one as I expect):
Models:
[Table("CustomerInventorys")]
public class CustomerInventory
{
public long ID { get; set; }
public long CustomerID { get; set; }
public virtual ICollection<CycleCount> CycleCounts { get; set; }
}
[Table("CycleCounts")]
public class CycleCount
{
public long ID { get; set; }
public long CustomerInventoryItemID { get; set; }
public virtual CustomerInventory CustomerInventoryItem { get; set; }
}
So if my suggestions are correct I recommend you to rewrite you code like this:
IQueryable<CycleCount> results = null;
if (customerIDs != null && customerIDs.Length > 0)
{
results = from invent in DB.CustomerInventorys
where customerIDs.Contains(invent.CustomerID)
join cycle in DB.CycleCounts on invent.ID equals cycle.CustomerInventoryItemID
select cycle;
}
else
results = DB.CycleCounts;
var cycleCounts = await results.ToListAsync();

View complex Many to Many relationship on ADO.net

I'm trying to update related database on many to many relationship using ADO.net
this is my database design:
as you guys notice, entity framework wont mapping the class_student & subject_course, i've been searching the method and found this website: http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/updating-related-data-with-the-entity-framework-in-an-asp-net-mvc-application
the website told me to make a viewModel, and i do so:
namespace Test.Models.ViewModels
{
public class AssignedStudentData
{
public int ID { get; set; }
public string course_code { get; set; }
public bool Assigned { get; set; }
}
}
It's work flawlessly, but my problem is this line of code:
private void PopulateAssignedStudentData(ms_class ms_class)
{
var allStudent = db.ms_student; //this line is the problem
var ClassStudent = new HashSet<int>(ms_class.ms_student.Select(c => c.ID));
var viewModel = new List<AssignedStudentData>();
foreach (var student in allStudent)
{
viewModel.Add(new AssignedStudentData
{
ID = student.ID,
course_code = student.ms_course.course_name,
Assigned = ClassStudent.Contains(student.ID)
});
}
ViewBag.Students = viewModel;
}
in var allStudent, i've tried to make so the system not generate all the student, but instead, student THAT ASSIGNED WITH A SUBJECT so for example:
private void PopulateAssignedStudentDataBySubject(ms_class ms_class, int subject_id)
{
//var allStudent = db.ms_student; //this line is the problem
//My Version:
var allStudentByCourse = db.ms_student.Include(m => m.ms_course).Where(m => m.ms_course.ms_subject.subject_id == subject_id); //this code is not working
var ClassStudent = new HashSet<int>(ms_class.ms_student.Select(c => c.ID));
var viewModel = new List<AssignedStudentData>();
foreach (var student in allStudentByCourse )
{
viewModel.Add(new AssignedStudentData
{
ID = student.ID,
course_code = student.ms_course.course_name,
Assigned = ClassStudent.Contains(student.ID)
});
}
ViewBag.Students = viewModel;
}
i think the code won't work because the ms_course and ms_subject is a many-to-many relationship..
Thank you very much
Class
public partial class ms_course
{
public ms_course()
{
this.ms_student = new HashSet<ms_student>();
this.ms_subject = new HashSet<ms_subject>();
}
public int course_id { get; set; }
public string course_code { get; set; }
public string course_name { get; set; }
public virtual ICollection<ms_student> ms_student { get; set; }
public virtual ICollection<ms_subject> ms_subject { get; set; }
}

I understand that you're looking for students having a course that has at least one specific subject assigned to it. That would be:
db.ms_student
.Where(s => s.ms_course.ms_subject
.Any(sb => sb.subject_id == subject_id)))
It always helps me to articulate the problem clearly in terms of the object model first, as I did in the first sentence. It usually reveals what the query should look like.

What does the error message say?
You can try tis:
var allStudentByCourse = db.ms_student.Include(m => m.ms_course).Include("ms_course.ms_subject").Where(m => m.ms_course.ms_subject.subject_id == subject_id);
alternativ2 (this only works if ms_course has a fk property to ms_subject):
var allStudentByCourse = db.ms_student.Include(m => m.ms_course).Where(m => m.ms_course.subject_id == subject_id);
Update:
var allStudentByCourse = db.ms_student.Include(m => m.ms_course).Include("ms_course.ms_subject").Where(m => m.ms_course.ms_subject.Any(s => s.subject_id == subject_id));

Linq "join" with a IList<T> getting "Error Unable to create a constant value.."

I have a Save Method that saves with a Linq query a manually re-orderd list (in a web form) that is passed as the parameter to my method, and I try to update the Order Property of the IEnumerable<VM_CategoryLabel> I retrieve from the database (EF) with the corresponding value in the list (maybe would that be clearer with my code below):
public static void SaveFromList(IList<VM_CategoryLabelExtra> listTemplate)
{
int idCat = listTemplate.Select(x => x.IdCat).FirstOrDefault();
var test = (int)listTemplate.Where(z => z.Id == 8).Select(z => z.Order).FirstOrDefault();
using (var context = new my_Entities())
{
var requete = from x in context.arc_CatLabel
where x.ID_Categorie == idCat
orderby x.Sequence_Cat
select new VM_CategoryLabel
{
Id = x.ID_LabelPerso,
//Order = x.Sequence_Cat,
Order = (int)listTemplate.Where(z => z.Id == x.ID_LabelPerso).Select(z => z.Order).First(),
Label = x.arc_Label.Label,
Unit = x.arc_Label.Unit
};
context.SaveChanges();
}
}
I used the "test" var to see if my "sub-query" gets the correct value, and it does, but when I use my Linq expression inside the Select (the commented Order line), I get the following error:
Unable to create a constant value of type 'Namespace.Models.VM_CategoryLabelExtra. "Only primitive types and enumeration types are supported in this context.
Here are my classes:
public class VM_CategoryLabel
{
public int Id { get; set; }
public int Order { get; set; }
public string Label { get; set; }
public string Unit { get; set; }
public bool Checked { get; set; }
}
public class VM_CategoryLabelExtra
{
public int Id { get; set; }
public int IdCat { get; set; }
public int Order { get; set; }
public string Label { get; set; }
public string Unit { get; set; }
public bool Checked { get; set; }
}
So I suppose that I should not query the list inside my query ? So how do I "match" the 2 lists of values ?
I also tried the following (after having replace in the Linq query: Order = x.Sequence_Cat)that is not working neither because the iteration variable is
read-only:
foreach (var item in requete)
{
item.Order = listTemplate.Where(x => x.Id == item.Id).Select(x => x.Order).FirstOrDefault();
}
try
{
context.SaveChanges();

I suggest using this.
It is the let clause.
public static void SaveFromList(IList<VM_CategoryLabelExtra> listTemplate)
{
int idCat = listTemplate.Select(x => x.IdCat).FirstOrDefault();
var test = (int)listTemplate.Where(z => z.Id == 8).Select(z => z.Order).FirstOrDefault();
using (var context = new my_Entities())
{
var requete = from x in context.arc_CatLabel
where x.ID_Categorie == idCat
orderby x.Sequence_Cat
let list = listTemplate
select new VM_CategoryLabel
{
Id = x.ID_LabelPerso,
Order = list.Where(z => z.Id == x.ID_LabelPerso).Select(z => z.Order).First(),
Label = x.arc_Label.Label,
Unit = x.arc_Label.Unit
};
context.SaveChanges();
}
}
edit: instead offrom you can just do let list = listTemplate
Should work now :)

example for let:
// The let keyword in query expressions comes in useful with subqueries: it lets
// you re-use the subquery in the projection:
from c in Customers
let highValuePurchases = c.Purchases.Where (p => p.Price > 1000)
where highValuePurchases.Any()
select new
{
c.Name,
highValuePurchases
}
If you do not know how Let working than please download LinqPad and see an example