Linq Intersection

Quick question

I have a list

List<System.Guid> guidList;

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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?
infinidemAsked:
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it_saigeDeveloperCommented:
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);
	}
}

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Produces the following output:Capture.JPG
-saige-
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Fernando SotoRetiredCommented:
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();

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infinidemAuthor Commented:
Would that be the same as:

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

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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();

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Fernando SotoRetiredCommented:
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.
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infinidemAuthor Commented:
is there any code efficency that can be added to the delete?  Doing the foreach loop seems excessive.
0
Fernando SotoRetiredCommented:
None that I can think of. All it is doing is setting a flag to mark it for deletion.
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