Solved

Linq Intersection

Posted on 2014-10-24
6
245 Views
Last Modified: 2016-02-15
Quick question

I have a list

List<System.Guid> guidList;

Open in new window


I have a DB with a table that has a GUID field.

I want a list of items where the guid is on the list.

Would you use any, join, intersect?
0
Comment
Question by:infinidem
  • 3
  • 2
6 Comments
 
LVL 33

Expert Comment

by:it_saige
ID: 40402374
If we are talking about a list that contains guids then a simple where clause will suffice:
using System;
using System.Collections.Generic;
using System.Linq;

static class LinqExample
{
	private static List<TestData> DataElements = new List<TestData>();

	public static void Main()
	{
		Guid guid1 = Guid.NewGuid();
		Guid guid2 = Guid.Empty;
		Guid guid3 = Guid.NewGuid();

		for (int i = 0; i < 30; i++)
		{
			if (i % 3 == 0)
				DataElements.Add(new TestData(guid3, string.Format("Data element {0} for guid 3.", (from de in DataElements where de.Guid == guid3 select de).Count() + 1)));
			else if (i % 2 == 0)
			{
				if (guid2 == Guid.Empty)
					guid2 = Guid.NewGuid();

				DataElements.Add(new TestData(guid2, string.Format("Data element {0} for guid 2", (from de in DataElements where de.Guid == guid2 select de).Count() + 1)));
			}
			else
				DataElements.Add(new TestData(guid1, string.Format("Data element {0} for guid 1.", (from de in DataElements where de.Guid == guid1 select de).Count() + 1)));
		}

		Console.WriteLine("Data elements for Guid 1");
		Console.WriteLine("------------------------");
		foreach (var de in (from de in DataElements where de.Guid == guid1 select de))
			Console.WriteLine(de);

		Console.WriteLine(string.Empty);
		Console.WriteLine("Data elements for Guid 2");
		Console.WriteLine("------------------------");
		foreach (var de in (from de in DataElements where de.Guid == guid2 select de))
			Console.WriteLine(de);

		Console.WriteLine(string.Empty);
		Console.WriteLine("Data elements for Guid 3");
		Console.WriteLine("------------------------");
		foreach (var de in (from de in DataElements where de.Guid == guid3 select de))
			Console.WriteLine(de);

		Console.ReadLine();
	}
}

class TestData
{
	private Guid _guid = Guid.Empty;
	private string _data = string.Empty;

	public Guid Guid
	{
		get { return _guid; }
	}

	public string Data
	{
		get { return _data; }
	}

	private TestData() { ;}

	public TestData(Guid guid, string data)
	{
		_guid = guid;
		_data = data;
	}

	public override string ToString()
	{
		return string.Format("{0} - {1}", _data, _guid);
	}
}

Open in new window

Produces the following output:Capture.JPG
-saige-
0
 
LVL 62

Accepted Solution

by:
Fernando Soto earned 500 total points
ID: 40402471
Hi infinidem;

Seeming that you have a List<Guid> in your program you can let Linq return those Guid's that are in your database that match your List. Here is a sample Linq query

// Your initialized list of Guid's
List<System.Guid> guidList;

List<System.Guid> results = (from g in db.YourTableName
                             where guidList.Contains(g.UniqueidentifierColumn)
                             select g.UniqueidentifierColumn).ToList();

Open in new window

0
 

Author Comment

by:infinidem
ID: 40402628
Would that be the same as:

var results = db.YourTableName.Where( abc => guidList.Contains(abc.UniqueIdentifierColumn));

Open in new window


I should add the results in this case would be to delete the items that match.

var results = db.YourTableName.Where( abc => guidList.Contains(abc.UniqueIdentifierColumn));

foreach (var result in results)
{
     db.DeleteObject(result);
 }

db.SaveChanges();

Open in new window

0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 62

Expert Comment

by:Fernando Soto
ID: 40402694
Hi ;

To your question, "Would that be the same as:", if you are looking for a List<YourTableName> records then yes.

To your statement, "I should add the results in this case would be to delete the items that match.", yes the results of the query which are records that match the Guid's that are in the guidList will be deleted from the database.
0
 

Author Comment

by:infinidem
ID: 40402936
is there any code efficency that can be added to the delete?  Doing the foreach loop seems excessive.
0
 
LVL 62

Expert Comment

by:Fernando Soto
ID: 40403021
None that I can think of. All it is doing is setting a flag to mark it for deletion.
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Convert to Hour/minute textbox and compare 3 52
Authentication of Web Services 3 49
Need a complete list of ASP.NET page load events 3 26
Host asp.net pages 5 25
Article by: Najam
Having new technologies does not mean they will completely replace old components.  Recently I had to create WCF that will be called by VB6 component.  Here I will describe what steps one should follow while doing so, please feel free to post any qu…
Summary: Persistence is the capability of an application to store the state of objects and recover it when necessary. This article compares the two common types of serialization in aspects of data access, readability, and runtime cost. A ready-to…
This is used to tweak the memory usage for your computer, it is used for servers more so than workstations but just be careful editing registry settings as it may cause irreversible results. I hold no responsibility for anything you do to the regist…
Hi friends,  in this video  I'll show you how new windows 10 user can learn the using of windows 10. Thank you.

911 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now