LINQ Project General Forum

using LINQ to query custom collection

Fri, 27 Nov 2009 05:40:12 Z

I have a question for the LINQ lovers. Consider that I have a custom collection Products class which in turn is a collection of a class Product.
Products
Product

Till here is fine, If i extend it further and have Product as a collection of a class named Variant. Thus now I have:
Products
Product
Variant

Now I finally have the three classes Products , Product and Variant. Products is the collection of Product class , Product is the collection of Variant clss.

If I have a variantID e.g VAR-12 and I would like to use my favourite LINQ to query the Products collection to get the Product which has the variant id as VAR-12.

are you ready :)))

zeeshan [ visit my forum: www.code4project.com ]

LINQ2 SQL for a n-tier Application?

Thu, 26 Nov 2009 08:20:37 Z

Hi there,

i want to use LINQ2SQL for an O/R Mapper in an n-Tier Application.
Now i am little bit scarried because i have to maintain a reference to an DataContext.
Is there a common guideline how to use LINQ2SQL for n-tier applications?

Sync Problems/Question with LINQ2SQL

Sat, 28 Nov 2009 23:21:26 Z

I'm trying to understand the behavior of having two separate processes (different computers, same sqlserver 2008) update a record in a table. I can't seem to figure out the logic behind when the update is available to the other process. that is,

Computer A writes record
Computer B reads just written record (does not always see update).

I've noticed that when the application exits that wrote the record on Computer A, the record becomes visible. Obviously, the behavior is consistent, I'm just struggling with with what that consistency is. I've played with shared datacontext, not shared datacontext and still don't get it.

Thanks,

(and, I'm not using transactions explicityly)

Peter Kellner http://peterkellner.net Microsoft MVP • ASPInsider

How is it possible to call System.Xml.Linq.XElement.Elements method with string parameter even though there is no overload which takes string as parameter

Sat, 28 Nov 2009 08:12:40 Z

Hi All,
Can any one please clarify on the following:-
System.Xml.Linq.XElement class has a method - public IEnumerable<XElement> Elements(XName name)

which takes a parameter of type XName, however its possible to call the Elements method
with string parameter, even though there is no overload of this method which takes a string
parameter, then how is it possible?

Thanks.

Getting null references on subordinate object references in LINQ query results

Sat, 28 Nov 2009 01:34:16 Z

I'm very new to LINQ, so apologies if my nomenclature is out. However, I'm very experienced in SQL and C#.

I have two tables in an SQL relational database, tblUsers and tblPosts, regarding a blogging software piece I'm creating.

tblPosts has a column called "UserID", which refers to the User that created the Post.

I have provided a foreign key reference in SQL Server, that links the "UserID" in tblPosts, to the Primary "UserID" in tblUsers.

When creating my .edmx file in .NET 3.5 in VS2008, this relationship carries over correctly on the Designer diagram.

I translated tblPosts to "Post" and tblUsers to "User" on the .edmx Designed to help make my C# code more sensible to read.

Now, the problem I'm getting is that when I try to reference the "User" object "embedded" into a "Post" object after querying or running a foreach, I get a null on the User object. I cannot reference the User referenced by the Post, and I believe that I am supposed to (or why would LINQ make it possible to have such a convenient reference?)

Here's a code Example:

NearstarsEntities db = new NearstarsEntities() ;

foreach (Post p in db.PostSet)
{
User u = p.User; //<---- p is a valid object with valid data, but p.User is NULL!!!!

I've even tried doing a join, to see if that's the problem, but this also gives me a NULL User object:

NearstarsEntities db = new NearstarsEntities() ;

IQueryable<Post> ps = from posts in db.PostSet
join user in db.UserSet
on posts.User.UserID equals user.UserID
select posts ;

foreach (Post p in ps){

string sUsername = p.User.Username; //<---- p is a valid object with valid data, but p.User is NULL!!!!

Can anyone see what it is I'm doing wrong, or what I'm missing out?

Including only specific properties in LINQ-to-SQL joins

Thu, 26 Nov 2009 00:24:48 Z

I'm running the following query which is joing the Task table to the User table:

DataLoadOptions options = new DataLoadOptions();
options.LoadWith<Task>(o => o.User);
Domain.LoadOptions = options;

IQueryable<Task> query = 
    from o in Domain.Tasks
    select o;

This of course eagerly loads all Tasks and all joined Users. How can I join only a single property, such as User.Username?

I've tried "options.LoadWith<Task>(o => o.User.Username);" But this throws an exception. I also need to make sure the query returns Task objects though instead of anonymous objects.

How to execute a LINQ Query that is grouped by multiple columns

Fri, 27 Nov 2009 06:49:41 Z

I have the following query. nssRecords is a list of objects

var userGroupView = from record in nssRecords

orderby record.user_id

group record by new { record.user_id, record.import_dt } into userGroup

select userGroup;

when try to iterate through the query results, i get a type mismatch error.

foreach (IGrouping<string, NssRecord> productGroup in userGroupView)

{

foreach (var row in productGroup)

{

output.Text += row.user_id + "----" + row.import_dt + "----";

}

I get the following error:

Unable to cast object of type 'Grouping[<>f__AnonymousType0`2[System.String,System.String],Manual368ImportingApp.NssRecord]' to type 'System.Linq.IGrouping`2[System.String,Manual368ImportingApp.NssRecord]'.

If anyone knows how I can fix it, please let me know. This drives me crazy.

Lambda Expression on List Collection

Fri, 27 Nov 2009 10:24:02 Z

Hi,

I am new to Linq trying to learn good features. Could please help me to get an example on usage of

Expression<Func<List<class>,int, int>> expression, Here I need to do an operation on List<Class> at index 'Int' (second param).

Help let me know if you have any good info on this context as well.

Regards,

sreedhar

Memory issue with LINQ

Thu, 26 Nov 2009 06:23:43 Z

i have just start to work with LINQ. When i create a dataContext, it load all the table with the data to the memory at once, before even i start to manipulate the data.

this is my code...

myDataContext db = new myDataContext();

in the debug mode, when i look into "db", it shows all the table with all the data it self.

if i have more than 20 tables with more than 1000 records each, what will happed to the memory.

Or do i miss anything, or is there are anyway to manage the memory? Please help me on this issue?

/kevin

PrincipalContext.ValidateCredentials always true on XP

Tue, 22 Jan 2008 06:38:51 Z

I was messing around with .net 3.5's new System.DirectoryServices.AccountManagement when I ran into a problem with PrincipalContext.ValidateCredentials. I am able to validate a username and password on my laptop (windows XP SP2 joined to a domain), but when I run the same code on my desktop (Windows XP SP2 member of a workgroup) I am able to type in anything for the username and anything for the password (as long as I am authenticating against the local machine) and it will validate. Am I doing something wrong here? Here is the code:

Code Block

sing System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.DirectoryServices.AccountManagement;

namespace TryAccount

{

class Program

{

static PrincipalContext m_principalContext;

static UserPrincipal m_userPrincipal;

public static bool AuthenticateUser(string username, string password)

{

bool isAuthentic = false;

try

{

if (username.Contains("\\"))

{

string[] holdName = username.Split(new char[] { '\\' });

m_principalContext = new PrincipalContext(ContextType.Domain, holdName[0]);

isAuthentic = m_principalContext.ValidateCredentials(holdName[1], password, ContextOptions.Negotiate);

}

else

{

m_principalContext = new PrincipalContext(ContextType.Machine);

isAuthentic = m_principalContext.ValidateCredentials(username, password, ContextOptions.Negotiate);

}

if (isAuthentic)

{

m_userPrincipal = UserPrincipal.FindByIdentity(m_principalContext, username);

Console.WriteLine("User " + m_userPrincipal.Name + " gave a valid password.\n");

Console.WriteLine("Last logged on " + m_userPrincipal.LastLogon + "\n");

Console.WriteLine("Last bad password given " + m_userPrincipal.LastBadPasswordAttempt + "\n");

}

return isAuthentic;

}

catch (Exception ex)

{

Console.WriteLine(ex.ToString() + "\n");

return isAuthentic;

}

}

static void Main(string[] args)

{

string user = "";

string pass = "";

bool good = false;

while (true)

{

Console.WriteLine("Please enter a username:");

user = Console.ReadLine();

Console.WriteLine("Please enter " + user + "'s password:");

pass = Console.ReadLine();

good = Program.AuthenticateUser(user, pass);

Console.WriteLine("The result was " + good.ToString() + ".\nHit enter to continue.");

Console.ReadLine();

}

}

}

Distinct Query

Tue, 24 Nov 2009 09:39:01 Z

Hello all.

I have the following LINQ statement that appears to be working fine and dandy. Hwoever, someone has pointed out that my distinct may not be doing exactly what I want it to do (i.e. essentially group the UnitUserfield1).

Can someone explain the logic behind this and point me in the right direction as to how to amend this? The code is as follows:

 var query = (from r in db.tblOnlineReportingFINALPRODUCTs
                         where r.MemberId.Equals("FM00012")
                         select new { unitUserfield1 = r.UnitUserfield1 }).Distinct().OrderBy(r => r.unitUserfield1);

Does LINQ support the HDF5 file format?

Thu, 19 Nov 2009 18:46:05 Z

Does LINQ support the HDF5 file format?

Thanks,

Carmine Coniglio

Account Technology Strategist

Microsoft Corporation

1290 Avenue of the Americas

New York, NY 10104

Cell: 646 225-5066

carminec@microsoft.com

XElement.Add Problem

Wed, 18 Nov 2009 08:10:45 Z

Please tell me what I am doing wrong, but the syntax seems correct, however, no matter how I try to perform adding some elements to a larger group of elements, it cannot be done.

I also tried creating the small single elements and then adding to the larger group, but this wasnt allowed either. Perhaps there is a better method of doing this easy task.

            Dim status As XElement = _
                New XElement("status", _
                     New XAttribute("state", "full"), _
                        New XElement("pc", _
                            New XAttribute("mac", "0000000"), _
                            New XAttribute("serial", "123321") _
                        ), _
                        New XElement("test1", _
                            New XAttribute("state", "off"), _
                            New XAttribute("vol", "0") _
                        ), _
                        New XElement("test2", _
                            New XAttribute("state", "off"), _
                            New XAttribute("vol", "0") _
                        ) _
                     )

		' TEST 1
		' This doesnt work
                Dim x As XElement = New XElement("ext", _
                                                     New XAttribute("id", id), _
                                                     New XAttribute("cd", "") _
                                                    )
                status.Element("status").Add(x)

		
		' TEST 2
		' This doesnt work
                spaStatus.Element("status").Add(New XElement("ext", _
                                                     New XAttribute("id", id), _
                                                     New XAttribute("cd", "") _
                                                    )

Saving XDocument in My.Settings/user.config

Thu, 19 Nov 2009 03:06:30 Z

I am trying to save an XDocument into the application user settings. When I do this, nothing happens.

First I create the XDocument.

Dim x As XDocument = New XDocument(<test />)
My.Settings.x = New XDocument(x)
My.Settings.Save

After I review the user.config file the following is generated:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <userSettings>
        <MyApp.Settings>
            <setting name="x" serializeAs="Xml">
                <value />
            </setting>
        </MyApp.Settings>
    </userSettings>
</configuration>

So I know the setting is being accessed or else the setting x and the <value /> elements wouldnt exist. There is no exception thrown. So either you cannot store XML data w/in the XML Configuration file, but thought this would be serialized for storage, but maybe not, I have never attempted this. I can simply write to a file, but am not a fan of this approach, this is much cleaner and doesnt require adding more files to our application.

Thanks,

Steve

Linq to sql translation

Tue, 24 Nov 2009 12:26:20 Z

Hi i need a linq to sql query for this...

select LanguageName from Language where languageID not in(select LanguageId from Translation where SourceKey="SourceKey")

Please note that the innerquery returns me the (multiple) language id (bcoz source key is in multiple languages)

Thanks

expression cannot contain query expressions

Wed, 18 Nov 2009 22:17:59 Z

Hi All,
By any chance anybody can help with this issue:

1. There is entity framework context.
public partial class DataModelContainer : ObjectContext
..... blah

2. Other class use this context. HomeAddress is entity framework class. HomeAddressDTO use for projections from HomeAddress.

using( var context = new DataModelContainer() )
{
var addressRange = ( context.AddressSet.OfType<HomeAddress>().OrderBy( addr => addr.Id ).AsEnumerable<HomeAddress>().Skip<HomeAddress>( skip ).Take<HomeAddress>( take ) ).ToList<HomeAddress>();

var progectedRange = from address in addressRange select new HomeAddressDTO { Id = address.Id, City = address.City, Zip = address.Zip, PartyId = address.Party.Id };

return progectedRange.AsEnumerable<HomeAddressDTO>();

}

3. What I meant to do, take range from home address set and project to DTO.
But I get this "expression cannot contain query expressions" error. What is went wrong ?

Thanks,
Alex

Remove duplicate rows based on max(date)

Mon, 23 Nov 2009 13:17:48 Z

Hi Greetings!

I need a query to retain the records with latest date and deleted the duplicates with older dates
eg.
''''''''''''''''''''''''''''''''''''''''''''''''''''
id date row_id(unique)
1 11/11/2009 1
1 12/11/2009 2
1 13/11/2009 3
2 1/11/2009 4
'''''''''''''''''''''''''''''''''''''''''''''''''''
Expected result

1      13/11/2009    3
2      1/11/2009     4
''''''''''''''''''''''''''

Please help me
Sathia

LINQ orderby not working

Mon, 23 Nov 2009 03:40:41 Z

when I use LINQ orderby , for example col1
when sql server 2008 has an index on col1 and it sort by descending
LINQ return the result in descending order

Is it a bug or it is the way LINQ works?

Thanks very much

Convert datagridview to complex XML

Thu, 12 Nov 2009 12:09:30 Z

Dear all,

I have populated a datgridview with data.
I need to structure these data in a complex XML file as follows :

<root>
<From>External Entity</From>
<To>Internal Interface</To>
<Region One>
    <TP>200107070</TP>
    <Data>
      <Address></Address>
      <Stores>
        <Location>any location</Location>
        <Element>
          <Name>Prod-1</Name>
          <Value>20914221.00</Value>
        </Element>
        <Element>
          <Name>Prod-2</Name>
          <Value>5000.00</Value>
        </Element>
      </Stores>
    </Data>
</Region One>
</root>

How can this be done using LINQ..

Best regards

W.Seada

Convert SQL to LINQ

Tue, 24 Nov 2009 00:18:05 Z

I'm trying to convert the following SQL to LINQ, but so far I'm not getting the right results. Anyone know the best way to right this?

select p.*
from photo p
join
  (select pt.photoid
   from phototag pt
   join tag t on t.tagid = pt.tagid
   where t.description = 'keyword' or t.description = 'keyword2'
   group by pt.photoid
   having count(1) = 2) as pt on pt.photoid = p.photoid

Basically I have three tables. One contains photo information (photo), another that contains tags that describe the photos (tag), and the last one to specify which tags go with which photos (phototag). The search can be one or more keywords, but in the example above it's only 2. Search is always AND.

LinqDataSource doesn't handle original NULL values up updates for int, datetime, etc

Fri, 12 Oct 2007 15:01:25 Z

Has anyone else encoutered this problem:

I am using a LinqDataSource, and I have several rows that have null values for ints, datetimes, etc. When I try to do an update to that object from a formview, (even though I have now provided a value), LinqDataSource throws an exception from trying to cast the original NULL value to the type it is, which of course doesn't work for ints, datetimes, etc. This is pretty annoying, considering that I have to do stupid things to work around this such as using some generic date as a default value. I am assuming this is a bug. Has anyone else noticed this? Are there any work around or fixes?

Thanks,

John Sonmez

How to Sum the grouped field

Sun, 22 Nov 2009 14:04:37 Z

I've a list of tasks. Ie I've struct like
    struct Task
    {
        public DateTime Completed { get; set; }
        public string TaskKind { get; set; }
        public float Effort { get; set; }
    }

And I've a IList<Task>.

Now I want to group the tasks based on the date and group by TaskKind on each day with the summed effort.
For eg for I want to print like the below:

01-09-09     Design:10     Coding:5    Coordination:15
02-09-09     Coding:5       Meeting:2

Can anyone help me in constructing a LINQ query to achieve this?

Thanks.
Madhan

How do I do an IF EXISTS style query using LINQ?

Tue, 12 Aug 2008 10:56:57 Z

Hi all,

Quite often in SQL I need to be able to do a very quick query to determine if a given record exists meaning that I do something like:-

Code Snippet

IF EXISTS (SELECT 1 FROM tblUsers WHERE Username = "whatever")

RETURN 1

ELSE

RETURN 0

In SQL this is extremely fast and returns me a bit that tells me very simply if the record exists or not.

Could anyone tell me how I would write the same sort of thing in LINQ without having to return whole objects. At the moment all the samples seem to return the entire "User" object whereas I only want a bool value returned from the linq query.

Many thanks to anyone who can help

:-)

Simon

Any way to get multiple SUM()'s executed AND how to protect against no rows being returned

Sat, 14 Nov 2009 17:15:23 Z

I"m taking a chance and asking two questions here (not first normal form of forum question asking).

1. I've got the below sum's which causes 4 executions against the database. Is there anyway to have these sum's done in 1 query pass?

2. When I get 0 rows returns, the Sum() fails. What is a simple work around for this? I can't figure out what delegate possibly to pass to sum().

query.TotalHistoricalSpend = resultsQuery.Select(data => data.HistoricalSpend ?? 0.0).Sum();
query.TotalOptimalSpend = resultsQuery.Select(data => dataOptimalSpend ?? 0.0).Sum();
query.TotalSpend = resultsQuery.Select(data => data.Spend ?? 0.0).Sum();
query.TotalWeight = resultsQuery.Select(data => data.ShipmentWeight ?? 0.0).Sum();

Peter Kellner, MVP ASP.NET http://peterkellner.net

Remove method in LINQ to OBjects

Sat, 21 Nov 2009 03:02:43 Z

All I want to do is to remove an item from a generic collection using the Remove method. I can't find any clear docs on how to do that.

Could somebody please let me know how I can go about that?

Thanks,

Bill

Bill Yeager

Where / (i And 1) = 1)

Sat, 21 Nov 2009 23:37:23 Z

I am currently reading ProLINQ in VB2008. This book has the following code example:

Console.WriteLine("{0} : Begin", New StackTrace(0, True).GetFrame(0).GetMethod().Name)

Dim presidents() As String = { _

"Adams", "Arthur", "Buchanan", "Bush", "Carter", "Cleveland", _

"Clinton", "Coolidge", "Eisenhower", "Fillmore", "Ford", "Garfield", _

"Grant", "Harding", "Harrison", "Hayes", "Hoover", "Jackson", _

"Jefferson", "Johnson", "Kennedy", "Lincoln", "Madison", "McKinley", _

"Monroe", "Nixon", "Pierce", "Polk", "Reagan", "Roosevelt", "Taft", _

"Taylor", "Truman", "Tyler", "Van Buren", "Washington", "Wilson"}

Dim sequence As IEnumerable(Of String) = _

presidents.Where(Function(p, i) (i And 1) = 1)

For Each s As String In sequence

Console.WriteLine("{0}", s)

Console.WriteLine("{0} : End", New StackTrace(0, True).GetFrame(0).GetMethod().Name)

The results of this code is every other item in the array starting with Arhtur (Arhur, Bush, Cleveland, etc.)

What is the following command doing: (i And 1)

I understand i is the index of the given item in the array, however I do not understand when or how (i And 1) = 1.

Thanks for your help.

Extension method XElement

Thu, 19 Nov 2009 20:59:21 Z

Need a little hint here...
Normally I can create extension methods, but this one I'm having some trouble with:

var q = xml.Descendants(ns + "Event").ToList();

//q returns 1, everything is fine :)

var q1 = xml.Descendants(ns + "Events").Foo().ToList();

//q1 returns 0, something is wrong :(


public static class XMLExtension
    {
        public static IEnumerable<XElement> Foo<XElement>(this IEnumerable<XElement> value)
        {
            return value;
        }

    }

What is wrong?

Recommended way to do outer joins in LINQ to SQL

Sat, 21 Oct 2006 01:50:47 Z

First option:

    var query =
        from c in Data.Customers
        from p in c.Purchases.DefaultIfEmpty()
        select new
        {
            c.Name,
            p.Price
        };

This produces the SQL you'd expect, i.e.

    SELECT [t0].[Name], [t1].[Price]
    FROM [Customer] AS [t0]
    LEFT OUTER JOIN [Purchase] AS [t1] ON [t1].[CustomerID] = [t0].[ID]

Second option:

    var query =
        from c in Data.Customers
        from p in c.Purchases.DefaultIfEmpty()
        select new
        {
            c.Name,
            Price = (p == null ? null : p.Price)
        };

This type of query works over both IEnumerable and IQueryable, but the SQL it produces seems less efficient:

SELECT [t3].[Name], [t3].[value] AS [Price]
FROM (
    SELECT
        (CASE
            WHEN [t2].[test] IS NULL THEN NULL
             ELSE [t2].[Price]
         END) AS [value], [t0].[Name]
    FROM [Customer] AS [t0]
    LEFT OUTER JOIN (
        SELECT 1 AS [test], [t1].[CustomerID], [t1].[Price]
        FROM [Purchase] AS [t1]
        ) AS [t2] ON [t2].[CustomerID] = [t0].[ID]
    ) AS [t3]

Which is the recommended way to do an outer join? Should the query be written differently depending on whether it's going to run over LINQ to SQL or a local collection?

Joe

Linq to Excel - how?

Tue, 06 May 2008 16:19:54 Z

I will be receiving XML workbooks with various worksheets in them. I need to read data out of the various worksheets and generate bespoke formatted data from this. I will know the name of the work sheets and the column headers. I'd like to use LINQ to achieve this.

In my past life as a VB6 developer, I would have written an ADO query and retrieved a recordset and then worked with that. As a LINQ novice, my uninformed instinct would be to Save the excel spread sheet as an XML document (would probably get rid of the Excel version problem) and then query the XML using LINQ. But this may not be the best way....

My question therefore is "how best should I go about this?"

Many thanks

Griff

PS - I did attempt to save it as XML and query it using LINQ, but I think I fell foul of the namespaces. A quick look on MSDN baffled me further.....are there any good tutorials out there?

Variables in LINQ Lambda Expressions cause expression to re-evaluate dynamically if changed.

Tue, 10 Nov 2009 03:31:10 Z

I found an issue with LINQ dynamically re-evaluating the results of an expression when a variable used in the expression is changed after the expression is evaluated.

I put sample code on my blog.

http://babeattie.blogspot.com/2009/11/beware-reference-variables-in-linq.html

Is this intended behaviour, or a quirky bug? It is certainly something to be wary of when using lambda expressions in recursion.

SAMPLE CODE - changing the indx value after the count is evaluated changes the result set immediately!

private void button1_Click(object sender, EventArgs e)
{
System.Diagnostics.Debug.WriteLine("Testing:" + DateTime.Now.ToString());
List<Dictionary<int, int>> ld = new List<Dictionary<int, int>>();

ld.Add(new Dictionary<int, int>() { { 1, 10 }, { 2, 20 }, { 3, 30 } });
ld.Add(new Dictionary<int, int>() { { 1, 20 }, { 2, 300000}, { 3, 40000000 }, { 4, 500000000 }});

int indx = 10;

var ds = ld.Where(itm => itm[1] == indx);

if (ds.Count() > 0)
{
System.Diagnostics.Debug.WriteLine("Count=" + ds.First().Count());
indx = ds.First()[2]; //this is a value I want to keep for later
int valueIwant = ds.First()[3]; //this is the value I want from this result

System.Diagnostics.Debug.WriteLine("Value I Want=" + valueIwant);
//oh no ??? that's not the value I wanted ???
System.Diagnostics.Debug.WriteLine("Count=" + ds.First().Count());
//and now the count changed ???
}
}

Querying for a sublist

Wed, 18 Nov 2009 22:19:05 Z

Perhaps its just because its been a long couple of days, but I can't seem to figure this out... :)

Let's say I have the following (partial) classes, judging some kind of contest (forgive the hokey example, again, it's been a long day):

class SingleEvent

{

     public Double Score

     {

          get;

          set;

     }     

}



class Contestant

{

     public List<SingleEvent> AllScores

     {

          get;

          set;

     }



     public int ID

     {

          get;

          set;

     }

}

So, as you can see, a contestant gets a score for each individual event, and a list of those scores is kept in another class.

Now, for the entire contest, I have this class:

class AllContestants
{
     public List<Contestant> Contestants
     {
          get;
          set;
     }
}

I now want to create a query against AllContestants that will bring me back all the scores in descending score order (not grouped by events).

Make any sense at all?

Thanks,
WtS

more than 1 table in a gridview

Sat, 07 Nov 2009 09:42:19 Z

Hello

i search on the internet how i can get data from more than 1 table in a gridview, but i need it for a windows form. I don't understand one thing of asp.net. So can some of you give me a solution. And if it's possible that i can add columns so not hole the table but only column one, two and three for example.

Possible LINQ/SQL Server memory leak

Sat, 27 Oct 2007 19:02:52 Z

I'm using LINQ to SQL from VS 2008 with SQL Server 2005 (dev edition - sp2) and developing a web application, doing my testing with VS internal web server.

After 6-8 hours of developing, hitting the database quite alot, it suddenly becomes very unresponsive. I can fix it by restarting the SQL service, which leads me to believe there are unclosed/dead connection or LINQ to SQL is causeing problems.

The queries I perform are pretty basic (select from one or more tables with some custom projection and basic filtering), so I'm pretty sure thats not the source of the problem.

I try to limit the number of datacontexts I create, so for each request I only use one datacontext, like so:

Code Block

BTDataContext db = (HttpContext.Current.Items["DB"] ?? (HttpContext.Current.Items["DB"] = new BTDataContext())) as BTDataContext;

I unsure if that could be the source of the problem, but I dont think it is.

Any input will be much appreciated.

Best regards, Egil.

Custom properties in LINQ to SQL classes

Mon, 28 May 2007 11:52:50 Z

My Order table contains an OrderTypeID (int) field in the database. The OrderTypeIDs correspond to defined C# enum types (ie. OrderType.Internal). Using a partial class I can extend the LINQ to SQL Designer generated Order class to contain a OrderType property which returns a OrderType value instead of an int value. If I use the property in a query

var orderList =

from order in CurrentDataContext.Orders

where order.OrderType == OrderType.Internal

select order;

I get an exeption Binding error : Member '...Order.OrderType' is not a mapped member of '...Order'. The OrderType property works fine on a order object, but when querying with OrderType an exception is thrown.

Help

Thu, 19 Nov 2009 12:05:00 Z

Hi i need some kind of little help here, there are no errors but it has something that i don't like
when i trigger the btnReturnBook it will save to database the dateTime.Now
but when i trigger it again the column of my database indicates a null it only works on the first record
thanks.

private void btnReturnBook_Click(object sender, EventArgs e)
        {
            LSMDataContext ret = new LSMDataContext();
            HistoryTable newHisto = ret.HistoryTables.FirstOrDefault(n => n.BorrowedBook == listBox1.SelectedItem.ToString());
            newHisto.DateReturned = DateTime.Now.ToString();
            ret.SubmitChanges();
}

How much SQL i should know to do LINQ?

Wed, 18 Nov 2009 04:00:39 Z

Hi Friend,

I've learnt SQL up to an inermediate level : ) and i;m a .NET developer... with the Introduction of LINQ, according to what i've hear, programmers now no need to learn SQL....

So my qusetion is, is it possible to do all the things that we do in SQL from LINQ without knowing SQL to an adavance level?

thanks

Preserving unknown xml tags/data

Tue, 17 Nov 2009 04:48:48 Z

I deal with alot of different xml documents that are very dynamic. I end up creating some applications which allow the manipulation of the information in these xml files for use by other applications. I really like using the XElement class to allow me to read in the information and create objects out of the xml without any real stress. The problem is, how do I handle the new tags that get added later on. If I create an application that reads in X Y and Z tags, and then after everything has been changed, writes out the values I know about, how do I maintain any tags I don't have prior knowledge of?

Case in point, I had a file defined over a year ago. Project required more tags to be added to an xml doc. The application that read that xml file read in the file, wrote out a new one that deleted the new tags because it didn't know enough to save them.

I know I could use XPath and modify the document as it stands and get around the issue that way, but I don't want to deal with XPath. Is there a simple way to continue reading in the files as I have been, make objects out of the pieces I know about, save the pieces I don't know about where they are then put it back out to file when the changes are done?

Simple example. XML sample below was defined originally as:

<Sample>
   <TagA>Test</TagA>
</Sample>

after setting up the XDocument, I would basically create an object of whatever type and read in the tags similar to:
string t = (string)node.Element("TagA");

change it to whatever and make any other changes then write a new document out with the values from the objects.

Fast forward, xml spec changes and now the sample looks like:

<Sample>
   <TagA>Test</TagA>
   <TagB ID="0">New Tag</TagB>
</Sample>

After running the original app, the TagB is not read in, nor is it written out to the new file.

I don't care that it can't be edited without changing the application, but I need to have backwards compatibiity at least to the point that new information is not just blown away.

Any suggestions other than going longhand with XPath?

Thanks in advance.

Mark

LINQ SqlDateTime overflow

Fri, 28 Mar 2008 18:08:58 Z

Hi all,

I do somethink like:

MyTable _table = new MyTable;

_table.BornDate = new DateTime(1988, 9, 4); // yyyy , mm , dd

_database.MyTable.InsertOnSubmit(_table);

_database.SubmitChanges();

Compilation okay, but code throws an exception - SqlDateTime overflow, date must be between 1/1/1753 ....................

Debug fails on SubmitChanges();

Thanks

Or Where

Tue, 17 Nov 2009 10:26:46 Z

Hi

I have a bit of code that creates a series of where clauses dependent on user selections. Everything was working fine until I was asked to rather than a criterion on a field being > x how about x=1 or x=3 or x=5 as the query to return the data.

When I build the query adding the conditions (say I have selected initial query from a table in sql db using a datacontext)

                    For Each a In listOfPossibles
                        Dim val As Integer = a
                        query = query.Where(Function(f)f.MyIntFeild.Value = val)
                    Next

It does so by and and and. Is there a way to do this as Or?

I remember seing something about stings for the queries, so build the or and submit the string but I have no idea where to look for guidence on doing that?

Thanks for taking the time to read.

Anthony

I have seen some extension written in C

How to select max record after group by and convert back from annonymous type

Mon, 16 Nov 2009 18:26:06 Z

Hi I have some problems with a linq group by query trying to select for the most recent revision in some audit table.

Here is a brief description of the data schema,

I have a PO table, and a PO_audit table

PO_Audit table just tracks revisions of the PO table, the minimal schema of the PO audit table is:

{id(int), OriginalPOId(int),RevisionNumber(int)}

Here is a sample data

Id OriginalPOId Rev

1 1 1

2 1 2

3 1 3

4 2 1

5 2 2

In my query I'm trying to group by the original PO id and select for the most recent revision (I essentially want records with id = 3 and 5, the most recent rev of the PO)

so something like

var a =

from b in PO_Audit

group b by b.OriginalPOId into g

select new

{
mostRecentPO =

(

from d in g

where d.rev == g.max(r=>r.Rev)

select d).firstOfDefault
}

SO the above query will return a correct set of records, that is the most recent revision for each of the PO records but these are annonymous and I don't know how to convert them back to PO_Audit type other then using a for loop

foreach(var auditPO in a)

{

PO_Audit mostRecentAuditPerPO = (PO_Audit)auditPO.mostRecentPO;

}

I think I'm doing something wrong in my select query because auditPO should already be of type PO_Audit, I don't think I should have to access it using auditPO.mostRecentPO. (but I could not figure out how to select for the object without using mostRecentPO = in my annonymous inner query)

I'm looking for some way to cast these to the Ienumerable list of type PO_Audit, something like a.cast<PO_Audit>()

Thank you for any help on this.

Chris