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How to select needed records in joining table using LINQ with tables which have many to many relationship?

I have many to many relationship between entities user and group, I also have joining table GroupParticipants.
public class User
{
public string Id {get; set;}
public ICollection<GroupParticipant> Group { get; set;}
}
public class Group
{
public int Id { get; set; }
public ICollection<GroupParticipant> Participants { get; set; }
}
public class GroupParticipant
{
public int GroupId { get; set; }
public string ParticipantId { get; set; }
public User Participant { get; set; }
public Group Group { get; set; }
}
I need to select groups which user specified user did not join. I want to do something like:
string userId = 5;
var groupsAvailableToJoin = await _context.Groups
.Where(group => group.Participants.Id != userId);
Thanks!

A query like:
_context.Groups.Where(g =>
!_context.GroupParticipants.Any(gp => gp.UserId == userId && gp.GroupId == g.I'd
);
Should translate to:
SELECT * FROM Groups g
WHERE NOT EXISTS(SELECT null FROM groupParticipants gp WHERE gp.UserId = 5 AND gp.GroupId = g.Id)
Which should be a reasonably performant way of getting you what you're looking for.. I'm sure that the GroupParticipants columns are indexed..
There are various ways to write this - if you find a two step approach easier to understand, it's effectively the same as:
var joined = _context.GroupParticipants.Where(gp => gp.UserId == 5).Select(gp => gp.GroupId).ToList();
var notJoined = _context.Groups.Where(g => !joined.Contains(g.Id));
This one translates as a NOT IN (list,of,groups,they,are,in) for a similar effect

Calculated property for model EF Core - Property or Method?

I am new to EF core. I have a Customer model with the usual properties (Name,Address,Email).
I need a property to calculate the current balance for the customer.
This will be quite an intensive computation (once many records are stored) so am I correct in thinking that it should be stored in a Method, rather than a calculated property?
I am assuming I need to add a method such as .GetCurrentBalance().
Where would I put this method?
Simplified code below:
My Customer Model
public class Customer
{
public int CustomerId { get; set; }
public string Name { get; set; }
public string EmailAddress { get; set; }
public virtual IEnumerable<SalesInvoice> SalesInvoices{ get; set; }
}
My Sales Invoice Model
public class SalesInvoice
{
public int SalesInvoiceId { get; set; }
public int CustomerId { get; set; }
public virtual IEnumerable<SalesInvoiceDetail> SalesInvoiceDetails{ get; set; }
}
My Sales Invoice Detail Model
public class SalesInvoiceDetail
{
public int SalesInvoiceDetailId { get; set; }
public int Qty { get; set; }
public decimal UnitPrice { get; set; }
}

Create helper methods which returns desired results. Everything should play around IQueryable:
public class CustomerIdWithBalance
{
public int CustomerId { get; set; }
public decimal Balance { get; set; }
}
public class CustomerWithBalance
{
public Customer Customer { get; set; }
public decimal Balance { get; set; }
}
public static class BusinessLogicExtensions
{
public static IQueryable<CustomerIdWithBalance> GetCustomerIdAndBalance(this IQueryable<Customer> customers)
{
var grouped =
from c in customers
from si in c.SalesInvoices
from sid in si.SalesInvoiceDetails
group sid by new { c.CustomerId } into g
select new CustomerIdWithBalance
{
g.Key.CustomerId,
Balance = x.Sum(x => x.Qty * x.UnitPrice)
}
return grouped;
}
public static IQueryable<CustomerWithBalance> GetCustomerAndBalance(this IQueryable<CustomerIdWithBalance> customerBalances, IQueryable<Customer> customers)
{
var query =
from b in customerBalances
join c in customers on b.CustomerId equals c.CustomerId
select new CustomerWithBalance
{
Customer = c,
Balance = b.Balance
};
return query;
}
}
Later when you need to return that with API call (hypothetic samples)
var qustomerIdsWithHighBalance =
from c in ctx.Customers.GetCustomerIdAndBalance()
where c.Balance > 1000
select c.CustomerId;
var qustomersWithHighBalance =
ctx.Customers.GetCustomerIdAndBalance()
.Where(c => c.Balance > 1000)
.GetCustomerAndBalance(ctx.Customers);
var customersByMatchAndPagination = ctx.Customers
.Where(c => c.Name.StartsWith("John"))
.OrderBy(c => c.Name)
.Skip(100)
.Take(50)
.GetCustomerAndBalance(ctx.Customers);
You will get desired results without additional database roundtrips. With properties you may load too much data into the memory.
It is everything about using EF with its limitations. But world is not stopped because EF team is too busy to create performance effective things.
Let's install https://github.com/axelheer/nein-linq
And create extension methods around Customer
public static class CustomerExtensions
{
[InjectLambda]
public static TotalBalance(this Customer customer)
=> throw new NotImplmentedException();
static Expression<Func<Customer, decimal>> TotalBalance()
{
return customer =>
(from si in customer.SalesInvoices
from sid in si.SalesInvoiceDetails
select sid)
.Sum(x => x.Qty * x.UnitPrice));
}
}
And everything become handy:
var customersWithHighBalance =
from c in ctx.Customers.ToInjectable()
where c.TotalBalance() > 1000
select c;
var customersWithHighBalance =
from c in ctx.Customers.ToInjectable()
let balance = c.TotalBalance()
where balance = balance > 1000
select new CustomerWithBalance
{
Customer = c,
Balance = balance
};
var customersWithBalance =
from c in ctx.Customers.ToInjectable()
where c.Name.StartsWith("John")
select new CustomerWithBalance
{
Customer = c,
Balance = c.TotalBalance()
};
var paginated =
.OrderBy(c => c.Name)
.Skip(100)
.Take(50);

If you would prefer to calculate at property level. Add an InvoiceBal readonly field to the SalesInvoice model.
public class SalesInvoice
{
public double InvoiceBal => SalesInvoiceDetails.Sum(x => x.Qty * x.UnitPrice)
public virtual IEnumerable<SalesInvoiceDetail> SalesInvoiceDetails{ get; set; }
}
Add another TotalBalance readonly field to the Customer that sums the whole thing
public class Customer
{
public double TotalBal => SalesInvoices.Sum(x => x.InvoiceBal)
public virtual IEnumerable<SalesInvoice> SalesInvoices{ get; set; }
}

How to query data with calculated fields and map to a ViewModel with a nested ViewModel Collection?

I have referenced numerous questions on this site related to calculated fields and ViewModels, but I can't seem to extrapolate from examples given. I hope that laying out a specific scenario would allow someone to pin point what I can't see. I am new to WebApp design in general. Please take that into consideration. Also, if I've left off any relevant information, please let me know and I will update the question.
Here is the scenario:
I have a complex query that is spanning multiple tables to return data used in calculations. Specifically, I store units for a recipe converted to a base unit and then convert the quantity to the units specified by the user.
I am using AutoMapper to map from entities to ViewModels and vice versa, but I am not sure how to handle the calculated values. Especially with the nested ViewModel Collection thrown into the mix.
Option 1
Do I return an autonomous set of data? Like the following... and then somehow use AutoMapper to do the mapping? Perhaps I would need to do the mapping manually, which I haven't found a solid example which includes nested ViewModels. At this point, I'm not even sure if the following code handles the nested collection correctly for the autonomous data.
var userId = User.Identity.GetUserId();
var recipes = from u in db.Users.Where(u => u.Id == userId)
from c in db.Categories
from r in db.Recipes
join ur in db.UserRecipes.Where(u => u.UserId == userId) on r.Id equals ur.RecipeId
join mus in db.MeasUnitSystems on ur.RecipeYieldUnitSysId equals mus.Id
join muc in db.MeasUnitConvs on mus.Id equals muc.UnitSysId
join mu in db.MeasUnits on mus.UnitId equals mu.Id
join msy in db.MeasUnitSymbols on mu.Id equals msy.UnitId
select new
{
Id = c.Id,
ParentId = c.ParentId,
Name = c.Name,
Descr = c.Descr,
Category1 = c.Category1,
Category2 = c.Category2,
Recipes = new
{
Id = r.Id,
Title = r.Title,
Descr = r.Descr,
Yield = String.Format("{0} {1}", ((r.Yield * muc.UnitBaseConvDiv / muc.UnitBaseConvMult) - muc.UnitBaseConvOffset), msy.Symbol)
}
};
Option 2
Another option that crossed my mind was to return the entities and use AutoMapper as I normally would. Then iterate through the collections and perform the calculations there. I feel like I could make this work, but it seems inefficient to me because it would result in many queries back to the database.
Option 3
???? I can't think of any other method to do this. But, please, if you have suggestions, I am more than willing to hear them.
Relevant Data
Here is the query returning the data I want in SQL Server (more or less).
declare #uid as nvarchar(128) = 'da5435ae-5198-4690-b502-ea3723a9b217'
SELECT c.[Name] as [Category]
,r.Title
,r.Descr
,(r.Yield*rmuc.UnitBaseConvDiv/rmuc.UnitBaseConvMult)-rmuc.UnitBaseConvOffset as [Yield]
,rmsy.Symbol
FROM Category as c
inner join RecipeCat as rc on c.Id = rc.CategoryId
inner join Recipe as r on rc.RecipeId = r.Id
inner join UserRecipe as ur on r.Id = ur.RecipeId and ur.UserId = #uid
inner join MeasUnitSystem as rmus on ur.RecipeYieldUnitSysId = rmus.Id
inner join MeasUnitConv as rmuc on rmus.Id = rmuc.UnitSysId
inner join MeasUnit as rmu on rmus.UnitId = rmu.Id
inner join MeasUnitSymbol as rmsy on rmu.Id = rmsy.UnitId
inner join UserUnitSymbol as ruus on rmsy.UnitId = ruus.UnitId and rmsy.SymIndex = ruus.UnitSymIndex and ruus.UserId = #uid
ViewModels
public class CategoryRecipeIndexViewModel
{
public int Id { get; set; }
public int ParentId { get; set; }
[Display(Name = "Category")]
public string Name { get; set; }
[Display(Name = "Description")]
public string Descr { get; set; }
public ICollection<CategoryRecipeIndexViewModel> Category1 { get; set; }
public CategoryRecipeIndexViewModel Category2 { get; set; }
public ICollection<RecipeIndexViewModel> Recipes { get; set; }
}
public class RecipeIndexViewModel
{
public int Id { get; set; }
[Display(Name = "Recipe")]
public string Title { get; set; }
[Display(Name = "Description")]
public string Descr { get; set; }
[Display(Name = "YieldUnit")]
public string Yield { get; set; }
}
UPDATE 2/10/2018
I found an answer here that does a very good job of explaining exactly what I'm looking at. Particularly under the A Better solution ? section. Mapping queries directly to my ViewModels looks like it would allow me to get my calculated values as well. Problem is, the example given is once again too simplistic.
He gives the following DTO's
public class UserDto
{
public int Id {get;set;}
public string Name {get;set;}
public UserTypeDto UserType { set; get; }
}
public class UserTypeDto
{
public int Id { set; get; }
public string Name { set; get; }
}
And does the following for mapping:
var users = dbContext.Users.Select(s => new UserDto
{
Id = s.Id,
Name = s.Name,
UserType = new UserTypeDto
{
Id = s.UserType.Id,
Name = s.UserType.Name
}
});
Now what if the UserDTO looked like this:
public class UserDto
{
public int Id {get;set;}
public string Name {get;set;}
public ICollection<UserTypeDto> UserTypes { set; get; }
}
How would the mapping be done if the UserTypes were a collection?
Update 2/13/2018
I feel I am making progress, but am currently headed in the wrong direction. I found this and came up with the following (which currently errors because of the method call in the linq query):
*Note: I removed Category2 from the ViewModel as I found it was not needed and only complicated this further.
query inside index controller method
IEnumerable<CategoryRecipeIndexViewModel> recipesVM = db.Categories
.Where(x => x.ParentId == null)
.Select(x => new CategoryRecipeIndexViewModel()
{
Id = x.Id,
ParentId = x.ParentId,
Name = x.Name,
Descr = x.Descr,
Category1 = MapCategoryRecipeIndexViewModelChildren(x.Category1),
Recipes = x.Recipes.Select(y => new RecipeIndexViewModel()
{
Id = y.Id,
Title = y.Title,
Descr = y.Descr
})
});
Recursive Method
private static IEnumerable<CategoryRecipeIndexViewModel> MapCategoryRecipeIndexViewModelChildren(ICollection<Category> categories)
{
return categories
.Select(c => new CategoryRecipeIndexViewModel
{
Id = c.Id,
ParentId = c.ParentId,
Name = c.Name,
Descr = c.Descr,
Category1 = MapCategoryRecipeIndexViewModelChildren(c.Category1),
Recipes = c.Recipes.Select(r => new RecipeIndexViewModel()
{
Id = r.Id,
Title = r.Title,
Descr = r.Descr
})
});
}
At this point, I don't even have the calculations I require, but that doesn't matter until I get this working (small steps). I quickly discovered you can't really call a method inside a Linq Query. Then a thought occurs to me, if I need to force the Linq Query to execute and then perform all the mapping on the in memory data, then I would essentially be doing the same thing as Option 2 (above), but I could perform the calculations within the ViewModel. This is the solution I will pursue and will keep everyone posted.

You have to iterate over UserType Collection and map the value to UserType dto's collection.
Use this code.
var users = dbContext.Users.Select(s => new UserDto
Id = s.Id,
Name = s.FullName,
UserType = s.UserType.Select(t => new UserTypeDto
{
Id = t.Id,
Name = t.Name
}).ToList()
Hope this will help.

I got it working! ...I think. ...Maybe. If anything, I'm querying the data, mapping it to my ViewModels and I have the calculations too. I do have additional questions, but they are a lot more specific. I will layout the solution I followed and where I think it requires work below.
I basically implemented my Option 2 from above, but instead of iterating through the collections, I just performed the calculations within the ViewModels.
Controller Method
public ActionResult Index()
{
var userId = User.Identity.GetUserId();
var recipes = db.Categories.Where(u => u.Users.Any(x => x.Id == userId))
.Include(c => c.Category1)
.Include(r => r.Recipes
.Select(u => u.UserRecipes
.Select(s => s.MeasUnitSystem.MeasUnitConv)))
.Include(r => r.Recipes
.Select(u => u.UserRecipes
.Select(s => s.MeasUnitSystem.MeasUnit.MeasUnitSymbols)));
IEnumerable<CategoryRecipeIndexViewModel> recipesVM = Mapper.Map<IEnumerable<Category>, IEnumerable<CategoryRecipeIndexViewModel>>(recipes.ToList());
return View(recipesVM);
}
View Models
public class CategoryRecipeIndexViewModel
{
public int Id { get; set; }
public int ParentId { get; set; }
[Display(Name = "Category")]
public string Name { get; set; }
[Display(Name = "Description")]
public string Descr { get; set; }
public ICollection<CategoryRecipeIndexViewModel> Category1 { get; set; }
public ICollection<RecipeIndexViewModel> Recipes { get; set; }
}
public class RecipeIndexViewModel
{
public int Id { get; set; }
[Display(Name = "Recipe")]
public string Title { get; set; }
[Display(Name = "Description")]
public string Descr { get; set; }
public double Yield { get; set; }
public ICollection<UserRecipeIndexViewModel> UserRecipes { get; set; }
[Display(Name = "Yield")]
public string UserYieldUnit
{
get
{
return System.String.Format("{0} {1}", ((Yield *
UserRecipes.FirstOrDefault().MeasUnitSystem.MeasUnitConv.UnitBaseConvDiv /
UserRecipes.FirstOrDefault().MeasUnitSystem.MeasUnitConv.UnitBaseConvMult) -
UserRecipes.FirstOrDefault().MeasUnitSystem.MeasUnitConv.UnitBaseConvOffset).ToString("n1"),
UserRecipes.FirstOrDefault().MeasUnitSystem.MeasUnit.MeasUnitSymbols.FirstOrDefault().Symbol);
}
}
}
public class UserRecipeIndexViewModel
{
public MeasUnitSystemIndexViewModel MeasUnitSystem { get; set; }
}
public class MeasUnitSystemIndexViewModel
{
public MeasUnitIndexViewModel MeasUnit { get; set; }
public MeasUnitConvIndexViewModel MeasUnitConv { get; set; }
}
public class MeasUnitIndexViewModel
{
public ICollection<MeasUnitSymbolIndexViewModel> MeasUnitSymbols { get; set; }
}
public class MeasUnitConvIndexViewModel
{
public double UnitBaseConvMult { get; set; }
public double UnitBaseConvDiv { get; set; }
public double UnitBaseConvOffset { get; set; }
}
public class MeasUnitSymbolIndexViewModel
{
public string Symbol { get; set; }
}
This appears to be working, but I know it needs some work.
For instance, the relation shown between the Recipe and UserRecipe shows one to many. In reality, if the UserRecipe were filtered by the current user, the relationship would be one to one. Also, the same goes for the MeasUnit and the MeasUnitSymbol entities. Currently, I'm relying on the FirstOrDefault of those collections to actually perform the calculations.
Also, I have seen numerous posts that state that calculations should not be done in the View Models. Except for some who say it's okay if it is only a requirement of the View.
Last I will say that paying attention to variable names within the ViewModels would have saved me some headaches. And I thought I knew how to utilize Linq Queries, but had issues with the data returned. It was easier to rely on the eager loading provided by Entity Framework to bring back the hierarchical data structure needed, versus the flat table structures I'm used to working with.
I'm still new to a lot of this and wrapping my head around some of the quirks of MVC and Entity Framework leaves me brain dead after a few hours, but I will continue to optimize and adopt better programming methods as I go.

LINQ Query (Group BY) one column

Consider the following classes
public class DashboardTile
{
public int ID { get; set; }
public int? CategoryID { get; set; }
public string Name { get; set; }
public string Description { get; set; }
}
public class DashboardTileBO : DashboardTile
{
public bool IsChecked { get; set; }
public List<DashboardTileBO> DashboardTiles { get; set; }
}
I have list of tiles in which some tiles are child of other.Now I want to show my list of tiles in such a way that if it has childs it gets added to the list.
query I am trying
var allDashBoardTiles = (from a in context.DashboardTiles
group a by a.CategoryID into b
select new BusinessObjects.DashboardTileBO
{
ID = a.ID,
Name = a.Name,
Description = b.Description,
DashboardTiles = b.ToList(),
}).ToList();
var list = context.DashboardUserTiles.Where(a => a.UserID == userId).Select(a => a.DashboardTileID).ToList();
allDashBoardTiles.ForEach(a => a.IsChecked = list.Contains(a.ID));
Now in above query when I use group clause and in select if I use a.ID,a.Name etc it says that it doesnot contain definitionor extension method for it.
Table

You can't access the properties of a directly because GroupBy returns IGrouping<TKey,T>. You can include other columns also in your group by and access them like this:-
(from a in context.DashboardTiles
group a by new { a.CategoryID, a.ID, a.Name } into b
select new BusinessObjects.DashboardTileBO
{
ID = b.Key.ID,
Name = b.Key.Name,
DashboardTiles = b.ToList(),
}).ToList();
Edit:
Also, I guess the property DashboardTiles in DashboardTileBO class should be List<DashboardTile> instead of List<DashboardTileBO>, otherwise we cannot fetch it from DashboardTiles data.

How do I do a multi-join on two SQL Views in an Entity Framework Model?

I have two views in my model.
I basically need to do an INNER JOIN on them based on three columns:
dataSource
ShowID
EpisodeID
The first thing I don't know how to do is add the SQL "AND" operator to the LINQ expression.
The second thing is, I don't know how to SELECT the JOINED table.
Can someone give me a hand?
var query = (from s in db.TVData_VW_ShowList
from z in db.TVData_VW_Schedule
where s.dataSource = z.dataSource
&& s.ShowID = z.ShowID
&& s.EpisodeId = z.EpisodeId select ...

You can use anonymous types to your advantage here, both to join across multiple columns, and to project into a new type containing data from both sides of the join. Here's a working example using Linq to objects:
namespace LinqExample
{
class Program
{
static void Main()
{
var Shows = new List<ShowData> { new ShowData { dataSource = "foo", EpisodeID = "foo", ShowID = "foo", SomeShowProperty = "showFoo" }};
var Schedules = new List<ScheduleData> { new ScheduleData { dataSource = "foo", EpisodeID = "foo", ShowID = "foo", SomeScheduleProperty = "scheduleFoo" } };
var results =
from show in Shows
join schedule in Schedules
on new { show.dataSource, show.ShowID, show.EpisodeID }
equals new { schedule.dataSource, schedule.ShowID, schedule.EpisodeID }
select new { show.SomeShowProperty, schedule.SomeScheduleProperty };
foreach (var result in results)
{
Console.WriteLine(result.SomeShowProperty + result.SomeScheduleProperty); //prints "showFoo scheduleFoo"
}
Console.ReadKey();
}
}
public class ShowData
{
public string dataSource { get; set; }
public string ShowID { get; set; }
public string EpisodeID { get; set; }
public string SomeShowProperty { get; set; }
}
public class ScheduleData
{
public string dataSource { get; set; }
public string ShowID { get; set; }
public string EpisodeID { get; set; }
public string SomeScheduleProperty { get; set; }
}
}

So to join you can use the join keyword then use on to specify the conditions. && (the logical and operator in C#) will be translated to the SQL AND keyword.
Also, in EF they have what are known as "implicit joins" meaning if I have TableA with a foreign key to TableB, call it fKey.
Doing where TableA.fKey == TableB.pKey will cause the provider to put a join there. To select you simply need to do;
select new { prop1 = TableA.Prop1, prop2 = TableB.Prop1 }
this will create a new anonymous which selects values from both tables.
Below is a more complete example of the join syntax. I think it uses all of the things you asked about;
var result = from a in TableA
join b in TableB on a.fKey equals b.pKey && b.Status equals 1
select new { a.Prop1, a.Prop2, b.Prop1 };

First you need to create an auxiliar class that contains the columns of both views, something like:
public class viewItem
{
public int ShowID { get; set; }
public int EpisodeID { get; set; }
public int dataSource { get; set; }
...
}
then your linq query would be:
var query = (from s in db.TVData_VW_ShowList
join z in db.TVData_VW_Schedule
on s.dataSource equals z.dataSource
where s.ShowID == z.ShowID
&& s.EpisodeID == z.EpisodeID
select new viewItem {
ShowID = s.ShowID,
EpisodeID = s.EpisodeID,
dataSource = s.dataSource,
...
}