I create this class for a test.
I want to compare to List of the class and get different class between ListA and ListB. In my example the result get only class of ListB.
I do the same thin with list of string and work it
Class Example
public class FileNode
{
public string Source { get; set; }
public int Id { get; set; }
}
List<FileNode> ListA = new List<FileNode>
{
new FileNode{ Id = 1, Source="a" },
new FileNode{ Id = 2, Source="b" },
};
List<FileNode> ListB = new List<FileNode>
{
new FileNode{ Id = 1, Source="a" },
new FileNode{ Id = 2, Source="b" },
new FileNode{ Id = 3, Source="c" },
};
List<FileNode> ListAB = ListB.Where(m => !ListA.Contains(m)).ToList();
String example, it's works
List<string> a = new List<string> {"a","b","c","d","e" };
List<string> b = new List<string> {"a","b","c","d" };
List<string> ab = a.Where(m => !b.Contains(m)).ToList();
Well Contains is going to call Equals on the elements - and may also use GetHashCode (I doubt it, but you should override it consistently anyway). So you need to override Equals(object) and GetHashCode() in FileNode. (By default, you'll get reference equality.)
Note that as soon as you start trying to use Contains in a query which will execute in the database, it could behave completely different - it wouldn't be looking at your Equals/GetHashCode methods at that point.
Related
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();
If I have a class like this
`
class Person
{
public string First;
public string Last;
public bool IsMarried;
public int Age;
}`
Then how can I write a LINQ Expression where I could select properties of a Person. I want to do something like this (user can enter 1..n properties)
SelectData<Person>(x=>x.First, x.Last,x.Age);
What would be the input expression of my SelectData function ?
SelectData(Expression<Func<TEntity, List<string>>> selector); ?
EDIT
In my SelectData function I want to extract property names and then generate SELECT clause of my SQL Query dynamically.
SOLUTION
Ok, so what I have done is to have my SelectData as
public IEnumerable<TEntity> SelectData(Expression<Func<TEntity, object>> expression)
{
NewExpression body = (NewExpression)expression.Body;
List<string> columns = new List<string>();
foreach(var arg in body.Arguments)
{
var exp = (MemberExpression)arg;
columns.Add(exp.Member.Name);
}
//build query
And to use it I call it like this
ccc<Person>().SelectData(x => new { x.First, x.Last, x.Age });
Hopefully it would help someone who is looking :)
Thanks,
IY
I think it would be better to use delegates instead of Reflection. Apart from the fact that delegates will be faster, the compiler will complain if you try to fetch property values that do not exist. With reflection you won't find errors until run time.
Luckily there is already something like that. it is implemented as an extension function of IEnumerable, and it is called Select (irony intended)
I think you want something like this:
I have a sequence of Persons, and I want you to create a Linq
statement that returns per Person a new object that contains the
properties First and Last.
Or:
I have a sequence of Persns and I want you to create a Linq statement
that returns per Person a new object that contains Age, IsMarried,
whether it is an adult and to make it difficult: one Property called
Name which is a combination of First and Last
The function SelectData would be something like this:
IEnumerable<TResult> SelectData<TSource, TResult>(this IEnumerable<TSource> source,
Func<TSource, TResult> selector)
{
return source.Select(selector);
}
Usage:
problem 1: return per Person a new object that contains the
properties First and Last.
var result = Persons.SelectData(person => new
{
First = person.First,
Last = person.Last,
});
problem 2: return per Person a new object that contains Age, IsMarried, whether he is an adult and one Property called Name which is a combination
of First and Last
var result = Persons.SelectData(person => new
{
Age = person.Name,
IsMarried = person.IsMarried,
IsAdult = person.Age > 21,
Name = new
{
First = person.First,
Last = person.Last,
},
});
Well let's face it, your SelectData is nothing more than Enumerable.Select
You could of course create a function where you'd let the caller provide a list of properties he wants, but (1) that would limit his possibilities to design the end result and (2) it would be way more typing for him to call the function.
Instead of:
.Select(p => new
{
P1 = p.Property1,
P2 = p.Property2,
}
he would have to type something like
.SelectData(new List<Func<TSource, TResult>()
{
p => p.Property1, // first element of the property list
p -> p.Property2, // second element of the property list
}
You won't be able to name the returned properties, you won't be able to combine several properties into one:
.Select(p => p.First + p.Last)
And what would you gain by it?
Highly discouraged requirement!
You could achive similar result using Reflection and Extension Method
Model:
namespace ConsoleApplication2
{
class Person
{
public string First { get; set; }
public string Last { get; set; }
public bool IsMarried { get; set; }
public int Age { get; set; }
}
}
Service:
using System.Collections.Generic;
using System.Linq;
namespace Test
{
public static class Service
{
public static IQueryable<IQueryable<KeyValuePair<string, object>>> SelectData<T>(this IQueryable<T> queryable, string[] properties)
{
var queryResult = new List<IQueryable<KeyValuePair<string, object>>>();
foreach (T entity in queryable)
{
var entityProperties = new List<KeyValuePair<string, object>>();
foreach (string property in properties)
{
var value = typeof(T).GetProperty(property).GetValue(entity);
var entityProperty = new KeyValuePair<string, object>(property, value);
entityProperties.Add(entityProperty);
}
queryResult.Add(entityProperties.AsQueryable());
}
return queryResult.AsQueryable();
}
}
}
Usage:
using System;
using System.Collections.Generic;
using System.Linq;
namespace Test
{
class Program
{
static void Main(string[] args)
{
var list = new List<Person>()
{
new Person()
{
Age = 18,
First = "test1",
IsMarried = false,
Last = "test2"
},
new Person()
{
Age = 40,
First = "test3",
IsMarried = true,
Last = "test4"
}
};
var queryableList = list.AsQueryable();
string[] properties = { "Age", "Last" };
var result = queryableList.SelectData(properties);
foreach (var element in result)
{
foreach (var property in element)
{
Console.WriteLine($"{property.Key}: {property.Value}");
}
}
Console.ReadKey();
}
}
}
Result:
Age: 18
Last: test2
Age: 40
Last: test4
I have this query :
var query = (from tables ...
where ...
select new
{
ClientName = ClientName,
ClientNumber = ClientNumber,
ClientProduct = ClientProduct
}).Distinct();
which returns rows with 3 values.
ClientName and ClientNumber can be linked to multiple products.
So we can have :
NameA NumberA Product1
NameA NumberA Product2
NameA NumberA Product3
NameB NumberB Product4
NameC NumberC Product5
I would like to know if it is possible to store that in a List of a certain class which would be like :
class MyClass
{
string ClientName,
int ClientNumber,
List<int> ClientProducts
}
So there are no duplicate of ClientName and ClientNumber.
Thank you in advance.
With this class structure to represent your data:
class MyClass
{
public string ClientName { get; set; }
public int ClientNumber { get; set; }
public List<int> ClientProducts { get; set; }
}
class Procuct
{
public string ClientName { get; set; }
public int ClientNumber { get; set; }
public int ProductID { get; set; }
}
and this test data:
List<Procuct> Products = new List<Procuct>()
{
new Procuct() { ClientName = "A", ClientNumber = 1, ProductID = 1},
new Procuct() { ClientName = "A", ClientNumber = 1, ProductID = 2},
new Procuct() { ClientName = "A", ClientNumber = 1, ProductID = 3},
new Procuct() { ClientName = "B", ClientNumber = 2, ProductID = 4},
new Procuct() { ClientName = "C", ClientNumber = 2, ProductID = 5}
};
you can use the following linq query:
var q = from p in Products
group p by new
{
cName = p.ClientName,
cNumber = p.ClientNumber
} into pGroup
select new MyClass
{
ClientName = pGroup.Key.cName,
ClientNumber = pGroup.Key.cNumber,
ClientProducts = pGroup.Select(x => x.ProductID).ToList()
};
to get exactly what you want, i.e. a collection of MyClass objects.
The Grouping performed in the above linq query essentially guarantees that there will be no duplicates on (ClientName, ClientNumber).
Since you mention Linq-to-sql, most probably you Client entity already has the products linked. You might look for an overcomplicated solution.
It depends a bit on your foreign key stucture, but if your datamodel would be
Client has 1-many product and you have a Foreign key from product to client it is already present.
So you can just reference client.Products.
So in your case it would be
var query = (from Clients...
where ...
select new
{
ClientName = Client.ClientName,
ClientNumber = Client.ClientNumber,
ClientProduct = Client.Products.Select(s=>s.id).ToList()
});
But you might as well simply use your client entity with a eager load of the products.
It all depends on your datamodel + proper foreign key structure
if you have a many-many associations like Product-per-client between your client and product you can start from that entity. Have a look at this documentation - it provides a good starting point for Linq-2-sql.
http://weblogs.asp.net/scottgu/using-linq-to-sql-part-1
I solve same problem , I think it useful to you
Only check your Where Condition properly
Thank...
var query = (from tables ...
where ...
select new
{
ClientName = ClientName,
ClientNumber = ClientNumber,
ClientProduct = ClientProduct.ToList()
}).Distinct();
I have a message structure that contains the following
DateTime dateIn;
long? messageId;
string messageContent;
I am trying to group my message list based on messageId and ordered by the dateIn field.
My LINQ currently looks like this
var groups = from c in MessageList
let name = c.messageId
orderby name ascending, c.dateIn ascending
group c by name into g
select g;
When I try and feed it back into a new List< Messages>, the compiler comes back with
"Cannot implicitly convert type System.Collections.Generic.List<
System.Linq.IGrouping < long?, Messages> > to
System.Collections.Generic.List< Messages>"
Is the problem down to the long? more than anything? I have tried to cast messageId to long, but that doesn't seem to work either.
I suppose you can use SelectMany to orbitaine your Message collection from the grouped one (if I understood you correct):
List<Messages> back = groups.SelectMany(m=>m.ToList()).ToList();
UPDATED
According to your comments. When you use GroupBy - Linq creates the Enumerable of new generic type combining your collection type and key type, which you use for grouping. In your case it is Messages type and long? (the type of messageId - key, you are grouping by). So this should work for you:
List<long?,Messages> grouped = groups.ToList();
Or you can use var and this should work also:
var grouped = groups.ToList();
If I understand what are you trying to do, there is simpler way. Look at my demo:
public class Program
{
static void Main(string[] args)
{
List<Message> MessageList = new List<Message>()
{
new Message(){ dateIn = new DateTime(2000,1,11)},
new Message(){ dateIn = new DateTime(2000,1,9)},
new Message(){ dateIn = new DateTime(2000,1,8), messageId = 5},
new Message(){ dateIn = new DateTime(2000,1,12)},
new Message(){ dateIn = new DateTime(2000,1,2), messageId = 7}
};
foreach (var item in MessageList)
{
Console.WriteLine(item);
}
Console.WriteLine("===");
// MUCH SIMPLER
var result = MessageList
.GroupBy(m => m.messageId)
.SelectMany(m => m.ToList())
.OrderBy(m => m.dateIn);
foreach (var item in result)
{
Console.WriteLine(item);
}
Console.ReadLine();
}
}
struct Message
{
public DateTime dateIn { get; set; }
public long? messageId { get; set; }
public string messageContent { get; set; }
public override string ToString()
{
return messageId + "\t" + dateIn;
}
}
I have an list of objects which each have a list of attributes.
In the grid displaying the list of objects, I to show as the attributes as columns instead of showing them in a subgrid.
public class MyObject {
public int Id {get; set;}
public string Name {get; set;}
public IEnumerable<MyAttribute> Attributes {get; set;}
}
public class MyAttribute {
public int Id {get; set;}
public string Key {get; set;}
public string Value {get; set;}
}
So what I have is a IEnumerable<MyObject>. e.g.
var lst = new[]
{
new MyObject
{
Id = 1,
Name = "o1",
Attributes = new[]
{
new MyAttribute
{
Id = 1,
Key = "k",
Value = "v1"
},
new MyAttribute
{
Id = 2,
Key = "x",
Value = "v2"
},
}
},
new MyObject
{
Id = 2,
Name = "o2",
Attributes = new[]
{
new MyAttribute
{
Id = 3,
Key = "k",
Value = "v11"
},
new MyAttribute
{
Id = 4,
Key = "x",
Value = "v22"
},
}
}
};
And the grid I would like to end up with would then have 4 columns, Id, Name, k, x.
I have 2 problems...
The component I use to display the grid, uses ModelMetadataProviders.Current.GetMetadataForType((Func<object>) null, typeof (TModel)) to figure out which columns to show. How do I convince the ModelMetadataProviders to include these extra columns?
Similar, the code to get the values ModelMetadataProviders.Current.GetMetadataForProperties(this.Value, typeof (TModel)), how do I convince it to send those extra values?
If I can find a solution for the 2nd problem, I can probably find a workaround for the first one, since that is just a helper class.