I am looking forward to get a linq query for populating list of teachers and their respective divisons.
Here I have 2 classes Teacher and Division which are related by DivisionGroupID - GroupID
public class Teacher
{
public int ID { get; set; }
public string Name { get; set; }
public List<Division> lstDivison {get;set;}
public int DivisionGroupID { get; set; }
}
public class Division
{
public int GroupID { get; set; }
public string Name { get; set; }
public string Description { get; set; }
}
In main method List of both Teacher and Division will be populated
static void Main(string[] args)
{
Teacher obj = new Teacher { ID = 1, DivisionGroupID = 11, Name = "abcd" };
Teacher obj1 = new Teacher { ID = 2, DivisionGroupID = 12, Name = "efgh" };
List<Teacher> objList = new List<Teacher>();
objList.Add(obj);
objList.Add(obj1);
Division dv = new Division { GroupID = 11 ,Name="Division1",Description="first" };
Division dv1 = new Division { GroupID = 11, Name = "Division2", Description = "second" };
Division dv2 = new Division { GroupID = 11, Name = "Division3", Description = "third" };
Division dv3 = new Division { GroupID = 12, Name = "Division4", Description = "fourth" };
Division dv4 = new Division { GroupID = 12, Name = "Division5", Description = "fifth" };
Division dv5 = new Division { GroupID = 12, Name = "Division6", Description = "sixth" };
List<Division> lstDiv = new List<Division>();
lstDiv.Add(dv);
lstDiv.Add(dv1);
lstDiv.Add(dv2);
lstDiv.Add(dv3);
lstDiv.Add(dv4);
lstDiv.Add(dv5);
}
The requirement here is to get the list of teachers and populate the sublist of divisions each teachers holding. I got the solution based on 2 approaches.
Using sub query approach :
var upd = from teacher in objList
select new Teacher
{
ID = teacher.ID,
Name = teacher.Name,
lstDivison = (from div in lstDiv
where div.GroupID == teacher.DivisionGroupID
select new Division
{
Name = div.Name,
Description = div.Description
}).ToList()
};
Using Foeach loop through Teacher collection(objList) and updating the lstDivision
objList.ForEach(x => x.lstDivison = lstDiv
.Where(y => y.GroupID == x.DivisionGroupID)
.Select(p => new Division { Name = p.Name, Description = p.Description })
.ToList());
Both of these approaches will give me the result. But i am looking forward a better approach in as part of my project requirement which has to improve the query performance. Could you please suggest which is the best approach to handle this situation?
use yours teacher object to populate list of divisions under it. as my understanding that how it was designed class structure.
//populate property in object
objList.ForEach(x => {
x.lstDivison = lstDiv.Where(w=> w.GroupID == x.DivisionGroupID).ToList();
});
objList.Dump();
Related
I need some help to simplify a linq query. I have 2 classes Invoice and Customer.
The Invoice have a property CustomerId and a property Customer.
I need to get all invoices and include the Customer object.
I don't like my query, as it needs to change if new properties are added to the Invoice object.
I can't join the invoice and customer earlier than this stage so that is not an alternative.
My query.
var customers = GetCustomers();
var invoices = GetInvoices();
var joinedList = (from x in invoices
join y in customers on x.CustomerId equals y.CustomerId
select new Invoice
{
Amount = x.Amount,
CustomerId = x.CustomerId,
Customer = y,
InvoiceId = x.InvoiceId
}).ToList();
The classes
public class Invoice
{
public int InvoiceId { get; set; }
public double Amount { get; set; }
public int CustomerId { get; set; }
public Customer Customer { get; set; }
}
public class Customer
{
public int CustomerId { get; set; }
public string Name { get; set; }
}
private static IEnumerable<Invoice> GetInvoices()
{
yield return new Invoice
{
Amount = 34,
CustomerId = 1,
InvoiceId = 1
};
yield return new Invoice
{
Amount = 44.7,
CustomerId = 1,
InvoiceId = 2
};
yield return new Invoice
{
Amount = 67,
CustomerId = 2,
InvoiceId = 3
};
yield return new Invoice
{
Amount = 89,
CustomerId = 3,
InvoiceId = 4
};
}
private static IEnumerable<Customer> GetCustomers()
{
yield return new Customer
{
CustomerId = 1,
Name = "Bob"
};
yield return new Customer
{
CustomerId = 2,
Name = "Don"
};
yield return new Customer
{
CustomerId = 3,
Name = "Alice"
};
}
Why not just a simple foreach loop:
// Dictionary for efficient look-up
var customers = GetCustomers().ToDictionary(c => c.CustomerId);
var invoices = GetInvoices().ToList();
//TODO: error checking
foreach(var i in invoices)
i.Customer = customers[i.CustomerId];
I have a Complex Situation now and i am terribly stuck. Kindly Let me know if you can share some light to it.
I have a
List Which will have the Following properties
public class Categories
{
public string DisplayName { get; set; }
public string ValueCode { get; set; }
public string Count { get; set; }
}
This will have Values like
Category1/SubCategory1
cat1/sc1
5
Category1/SubCategory2
cat1/sc2
4
Category 2/Subcategory1
cat2/sc1
5
Category 2/Subcategory2
cat2/sc2
23
I created a Custom Class to fill in the values
public class JobCateogry
{
public string DisplayName { get; set; }
public string ValueCode { get; set; }
public string Count { get; set; }
public List<JobCateogry> SubCategories { get; set; }
}
I have to Split the String in the Code Value and assign it to the SubCategory.
Like My Final out of jobCategory would be
Category1
Cat1
9
SubCategory1
sub1
5
SubCateogry2
sub2
4
I tried to Split the string and assign it to the new class in two step first by splitting and then by assiging. But i am sure i am doing it the wrong way, because the moment i split, i loose the count .
var lstCategory = Categories
.Where(i => i.count > 0)
.Select(item => item.valueCode.Split('/')
.Select(k =>(k)).ToList();
List<JobCategories> jobcategories = lstCategory
.Select(item => item.Split(QueryStringConstants.CAT_SEPERATOR.ToCharArray()[0]))
.GroupBy(tokens => tokens[0].Trim(), tokens => tokens[1])
.Select(g => new JobCategories(g.Key, g.DisplayName,g.ToList(),)).ToList();
Can you please help?
A bit weird task
It might not be the best solution and it only works with the two layers :-), and i tried keeping a lot of linq for the fun of it
anyway hope it can get you moving forward.
full code snippet https://gist.github.com/cbpetersen/db698def9a04ebb2abbc
static void Main(string[] args)
{
var cats = new[]
{
new Categories { Count = "5", ValueCode = "cat1/sc1", DisplayName = "Category1/SubCategory1" },
new Categories { Count = "4", ValueCode = "cat1/sc2", DisplayName = "Category1/SubCategory2" },
new Categories { Count = "5", ValueCode = "cat2/sc1", DisplayName = "Category2/Subcategory1" },
new Categories { Count = "23", ValueCode = "cat2/sc2", DisplayName = "Category2/Subcategory2" }
};
var categories = cats.Select(x => x.DisplayName.Split('/')[0]).Distinct();
var list = new List<JobCateogries>();
foreach (var category in categories)
{
var a = new JobCateogries
{
ValueCode = cats.Where(x => x.DisplayName.Split('/')[0] == category)
.Select(x => x.ValueCode.Split('/')[0]).FirstOrDefault(),
DisplayName = category,
SubCategories = cats.Where(x => x.DisplayName.Split('/')[0] == category)
.Select(x => new JobCateogries
{
SubCategories = new List<JobCateogries>(),
Count = x.Count,
DisplayName = x.DisplayName.Split('/')[1],
ValueCode = x.ValueCode.Split('/')[1]
}).ToList(),
};
a.Count = a.SubCategories.Select(x => int.Parse(x.Count)).Sum().ToString();
list.Add(a);
}
list.ForEach(x => Print(x));
Console.ReadKey();
}
public static void Print(JobCateogries category, int indent = 0)
{
var prefix = string.Empty.PadLeft(indent);
Console.WriteLine(prefix + category.DisplayName);
Console.WriteLine(prefix + category.ValueCode);
Console.WriteLine(prefix + category.Count);
category.SubCategories.ForEach(x => Print(x, indent + 4));
}
I have a data like
public class PermList
{
public int UserId { get; set; }
public int GroupId { get; set; }
public int ModuleId { get; set; }
public int BitMaskedPermission { get; set; }
public List<PermList> TestData()
{
List<PermList> theList = new List<PermList>();
PermList sample1 = new PermList {BitMaskedPermission = 15, GroupId = 3, ModuleId = 2, UserId = 1};
theList.Add(sample1);
PermList sample2 = new PermList { BitMaskedPermission = 2, GroupId = 3, ModuleId = 1, UserId = 1 };
theList.Add(sample2);
PermList sample3 = new PermList { BitMaskedPermission = 48, GroupId = 2, ModuleId = 2, UserId = 1 };
theList.Add(sample3);
return theList;
}
}
I would like to apply OR to BitMaskedPermissions with grouping ModuleId. Here is what I would like to get;
How can I achieve this with using Linq.
TIA.
When you have an aggregation operation to perform that isn't one of the built-in ones (Sum, Max etc), you have to turn to Aggregate, which is more verbose but also much more powerful. Here, you want
var data = TestData();
var grouped =
from permList in data
group permList by new { permList.UserId, permList.ModuleId } into g
select new { // or a named class if you have one
g.Key.UserId,
g.Key.ModuleId,
BitMaskedPermission
= g.Aggregate(0, (acc, curr) => acc | curr.BitMaskedPermission)
};
Here, we pass Aggregate a function which takes the accumulator acc and the current value curr, and bitwise ORs them to get the ongoing accumulator value.
If you prefer the method-chaining syntax, it would look like (courtesy of #Chris):
var grouped = PermList.TestData()
.GroupBy(x=> new{x.UserId, x.ModuleId})
.Select(x=> new {
x.Key.UserId,
x.Key.ModuleId,
mask = x.Aggregate(0, (acc, curr)=>acc|curr.BitMaskedPermission)}
)
Maybe something like this:
PermList p=new PermList();
var result= (
from test in p.TestData()
group test by new{test.UserId,test.ModuleId} into g
select new
{
g.Key.UserId,
g.Key.ModuleId,
BitMaskedPermission= g.Sum (x =>x.BitMaskedPermission )
}
);
I been practicing with EF Code First, SQL Express, and ASP.Net MVC3.
When I run the website first the correct tables are generated by the FooInitializer and Student and Image are populated but for some reason the join table (StudentImages) is not being populated.
What could be the issue?
Tables: Student, Image, and StudentImages
public class Student
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Image> Images { get; set; }
}
public class Image
{
public int Id { get; set; }
public string Filename { get; set; }
public string Extension { get; set; }
public virtual ICollection<Student> Students { get; set; }
}
public class FooInitializer : DropCreateDatabaseIfModelChanges<DBContext>
{
protected override void Seed(DBContext context)
{
var students = new List<Student> {
new Student { Id = 1, Name = "John" },
new Student { Id = 2, Name = "Jane" }
};
students.ForEach(s => context.Students.Add(s));
context.SaveChanges();
var images = new List<Image> {
new Image { Id = 1, Filename = "IMG_4596.JPG", Extension = ".jpg" },
new Image { Id = 2, Filename = "IMG_4600.JPG", Extension = ".jpg" }
};
images.ForEach(i => context.Images.Add(i));
students[0].Images.Add(images[0]);
context.SaveChanges();
}
}
From what I can tell your Image class does not have a reference to the StudentID. Try adding:
public int StudentID { get; set; }
to the Image class maybe?
Also having an ICollection would mean that one image could have multiple students - is this correct? Maybe it should be a public virtual Student Student {...}
EDIT: Also I found this, with a many to many relationship (if thats what you need):
In your OnModelCreating() Method:
modelBuilder.Entity<Student>()
.HasMany(c => c.Images).WithMany(i => i.Students)
.Map(t => t.MapLeftKey("StudentId")
.MapRightKey("ImageID")
.ToTable("StudentImages"));
taken from this link that states:
A many-to-many relationship between the Instructor and Course
entities. The code specifies the table and column names for the join
table. Code First can configure the many-to-many relationship for you
without this code, but if you don't call it, you will get default
names such as InstructorInstructorID for the InstructorID column.
EDIT: Here is the code I used the other night, with my implementation of the code first MVC site:
var users = new List<User>
{
new User { UserID = new Guid(), Email = "me#me.com", LastOnline = DateTime.Now, Password = "pword", RegistrationDate = DateTime.Now, SecurityAnswer = "me", SecurityQuestion = "who?", Roles = new List<Role>() },
};
users.ForEach(s => context.Users.Add(s));
context.SaveChanges();
var roles = new List<Role>
{
new Role { RoleID = "Admin", Description = "Administration Users", Users = new List<User>() }
};
roles.ForEach(r => context.Roles.Add(r));
users[0].Roles.Add(roles[0]);
context.SaveChanges();
var userLicense = new List<UserLicense>
{
new UserLicense { AddDateTime = DateTime.Now, LicenseType = "Farmer", Manufacturer = "Motorola", Model = "Droid", PhoneIdentifier = "c0e4223a910f", UserID = users[0].UserID, User = new User() }
};
userLicense[0].User = users[0];
userLicense.ForEach(u => context.UserLicenses.Add(u));
context.SaveChanges();
userLicense[0].User = users[0];
context.SaveChanges();
Notice in each instantiated item, I am also instantiating a new referenced item within the parent object.
EDIT:
Ok try this:
var students = new List<Student> {
new Student { Id = 1, Name = "John", Images = new List<Image>() },
new Student { Id = 2, Name = "Jane", Images = new List<Image>() }
};
students.ForEach(s => context.Students.Add(s));
context.SaveChanges();
var images = new List<Image> {
new Image { Id = 1, Filename = "IMG_4596.JPG", Extension = ".jpg", Students = new List<Student>() },
new Image { Id = 2, Filename = "IMG_4600.JPG", Extension = ".jpg", Students = new List<Student>() }
};
images.ForEach(i => context.Images.Add(i));
students[0].Images.Add(images[0]);
students[1].Images.Add(images[1]);
context.SaveChanges();
Try adding this before saving changes for each student:
foreach (Image i in s1.Images)
context.ObjectStateManager.ChangeObjectState(i, System.Data.EntityState.Added);
Also try with System.Data.EntityState.Modified.
Hope this works...
I want to group by the categoryid and then do a count on this. But I don't know how to do this. I have tried a couple of ways without success. Here is my latest:
public class Count
{
public int TradersCount { get; set; }
public int Id { get; set; }
public string Description { get; set; }
}
public IQueryable<Count> CountTradersAttachedToCategories()
{
var data = from tc in _db.tblTradersCategories
select new Count
{
Description = tc.tblCategory.description,
Id = tc.tblCategory.categoryId,
TradersCount = tc.Select(x => x.categoryid).GroupBy().Count()
};
return data;
}
tblTradersCategories joins both
tblTraders/tblCategories
A single trader can have many categories
A single category can have many traders
Thanks in advance for any help.
Clare
Try this:
var data = from tc in _db.tblTradersCategories
group tc by new { tc.tblCategory.categoryId,
tc.tblCategory.description } into g
select new { Count = g.Count(),
Id = g.Key.categoryId,
Description = g.Key.description };
If you want that in your Count class you may need to use AsEnumerable() to perform the conversion in process:
var converted = data.AsEnumerable()
.Select(c => new Count { TradersCount = c.Count,
Id = c.Id,
Description = c.Description });
You can try doing them all in one go:
var data = from tc in _db.tblTradersCategories
group tc by new { tc.tblCategory.categoryId,
tc.tblCategory.description } into g
select new Count { TradersCount = g.Count,()
Id = g.Key.categoryId,
Description = g.Key.description };
But I don't know if that will work. It depends on how the LINQ provider handles it.