How To Update List Using Lambda Expression
Mar 15, 2011
I have two lists. lst contains ViewState Data i.e All the records of the gridview & second lstRank contains the list of integer(i.e ID) for only those records which are marked as checked (i.e Gridview contains a columns for checkbox). Now i want to update the lst bool status depending upon integer ID of lstRank. How it can be achieved by lambda expression
List<Tuple<int, string, bool>> lst = (List<Tuple<int, string,bool>>)ViewState["gvData"];
List<int> lstRank = gvDetails.Rows.OfType<GridViewRow>().Where(s => ((CheckBox)s.FindControl("chkSelect")).Checked)
.Select(s => Convert.ToInt32(((Label)s.FindControl("lblRankCD")).Text)).ToList();
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Mar 14, 2011
I am selecting the checked rows from Gridview. To achieve this i have written a lambda expression using dynamic keyword.
var dn = gvLoans.Rows.OfType<dynamic>().Where(s => s.FindControl("chkSelect").Checked == true).Select(s => s.FindControl("lblCD")).ToList();
I want the output of this in List. Can it be achieved by extending the query or i have to write foreach statement.
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Feb 6, 2011
I have a dictionary with integers representing ProductId's.
I want to get all the Products that are listed in this dictionary. What is the best way of doing this?
I have tried the following which doesnt work:
gvBasket.DataSource = ent.Products.Where(x => x.ProductId in Dic.Keys);
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Sep 29, 2010
i have the following, which works:
@{Html.RenderAction("Detail", "Help", new { pageName = "press" });}
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@{Html.RenderAction<HelpController>(x => x.Detail("press"));}
But i get the following error:
The non-generic method 'System.Web.Mvc.Html.ChildActionExtensions.RenderAction(System.Web.Mvc.HtmlHelper, string, string, System.Web.Routing.RouteValueDictionary)' cannot be used with type arguments
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Oct 26, 2010
I Use entity framework 4.
Here is my model
Language
LangID
LangName
Product
PrdID
IsActive
ProductText
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LangID
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CatID
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Each time I want the text for one of these model, I execute this lambda expression p=> p.LangID == 1
Is it possible to create a generic lambda expression function that all of these model can use.?
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Mar 23, 2011
I did a small experiment to test whether lamdba expression can retrieve faster results than foreach statement. but, Lambda failed
[Code]....
why lambda is slower than foreach. This may be a drawback of lambda expression
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Nov 18, 2010
I need to get two fields from a database table (retrieved using linq-to-sql), one field is a datetime (and is a fixed field) and the other is always a decimal, but the field can be different.
The table holds currency data which is processed twice a day and in different currencies so could have fields such as AM_USD, PM_USD, AM_EUR etc. And I need to get data such as a list of the date against PM_USD or the date against AM_EUR.
I would like to be able to call the data using a lambda expression for example (this is a stripped out example):
data = TableData.Select(x=>new {x.DateTimeAdded, x.[**field name as string**]});
I have been trying to write a function to do this, and am failing dismally.
The closest I have managed is:
private Func<TableData, KeyValuePair<DateTime, decimal>> CreateSelect(string FieldName)
{
var parameterExp = Expression.Parameter(typeof(TableData), "sel");
var dateParameter = Expression.Parameter(typeof(DateTime), "DateTimeAdded");
var fieldParameter = Expression.Parameter(typeof(decimal), FieldName);
ConstructorInfo constructorInfo = typeof(KeyValuePair<DateTime, decimal>).GetConstructor(new[] { typeof(DateTime), typeof(decimal) });
NewExpression constructExpression = Expression.New(constructorInfo, new ParameterExpression[] { dateParameter, fieldParameter});
var lambda = Expression.Lambda<Func<TableData, KeyValuePair<DateTime, decimal>>>( constructExpression, parameterExp);
return lambda.Compile();
}
Which fails with "System.InvalidOperationException: Lambda Parameter not in scope".
I'm sure I missing something obvious, or going about it wrong way.
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Aug 6, 2010
I'm new to LINQ and EF and I seem to be having trouble working this out.
I have a many-to-many relationship between my Location and Region tables. When adding or editing a Location, my interface allows the user to check any number of related Regions. If they click OK, I need to add any new relationships that were checked, and delete any existing relationships that have been unchecked. My basic code is shown below.
However, this code doesn't work. Lower down, the line location.Regions.Contains(region) returns false even when the location already is related to the region. The issue appears to be because the region is from my populated listbox that was initialized earlier and is no longer part of the current EF context. But if I try and add it, I get an error that there is already a Region with that ID.
It seems like what I want to do is change this line to something like location.Regions.Contains((r) => r.RgnID == region.RgnID) so I'm only testing for a particular ID. But this gives me the error "Cannot convert lambda expression to type 'TrailCalendar.Region' because it is not a delegate type."
I don't understand this error but, either way, I'm not sure how I can test if the relationship already exists without reloading a bunch of data, which I'd like to avoid.
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Aug 17, 2010
I am new to LINQ to XML in .net(C#, asp.net). I want to know more about Lambda expressions. I am using Lambada expression with the following query.
count = FieldRoot.Element("USER").Element("MM")
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how the Lambda expression work specially in case of parameters (in the above case a & b) ? What is the basic concept of parameters in Lambda expression ? Can we use the names of the variables defined outside of the query instead of a & b ? which elements a & b represent in the above case represent ? Can we pass parameters from outside in the query ? If we can pass parameters from outside query then how it will be done? If you give me any other example instead of the above query to understand the concept of parameter in Lambda expression.
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Jun 29, 2010
What will be the equivalent GroupJoin lambda expression in LINQ when I do this.
Dim fruit_salad = (From fruits In _DataContext_Fruits _
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From fruitty_lecious In Group.DefaultIfEmpty() _
[code]...
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Feb 5, 2011
Given:
string removeRows = "";
int i = 0;
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{
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{
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}
what's the Lambda syntax to execute the removal?
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Jan 28, 2010
I have 2 tables; they have a many-to-many relationship. One is called Blog the other is Tag.
A Blog can contain a List of Tag objects. How can I go about getting all blogs that have a passed in tag name using lambda expressions?
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Jun 12, 2010
I get this error: "Cannot convert lambda expression to type 'string' because it is not a delegate type" - keyword select become underlined in blue.
[code]....
Above code should displays drop list of employees first name and last name in a combo box
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Nov 11, 2010
Say I have a table Comments with these columns: Id, Comment, Category, CreatedDate, CommenterIdI want to get the top 5 categories from the Comments table (based on the count of each category in that table). How can I do this in linq, to return either List or IQueryable?
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Apr 25, 2010
In the "Regular Expression Editor" dialog in VS 2008 ( or 2005 for this matter ) ,
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Anyone knows how to alter that list ?
I've found some question about it on the web - and the answer given is that it's not possible .
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Jun 18, 2010
Im trying to make some BBCode-translation from textarea, but im stuck on translate list to html. I have this fo Bold text:
[Code]....
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Mar 29, 2011
var pq = attributes.SingleOrDefault(a => a.AttributeName == PasswordQuestion").AttributeValue;
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Aug 25, 2010
I write inline expression and binding expression in the server head section:
[Code]....
[Code]....
But both kinds of expression aren't parsed or executed except the ResovleUrl menthod. The html renders like this:
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Feb 16, 2010
I'm trying to use the validator to work on a email form to ensure that they enter a valid from email address. That part works. I also want to add to the expression the text that I pre-populate in the txtbox ("Enter your email address") so on postback, after sending the message, I can clear the fields and repopulate that box.
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Jul 13, 2010
Just wanted to get clarification that methods like HTML.TextBoxFor() exist ONLY for the benefit of compile-time parameter type checking.
From my experimentation, these appear to ONLY accept a simple "expression lambda" syntax, which simply provides reference to a member property, and will not allow more robust use of "statement lambda" syntax. Other places in the .NET framework where lambda's are used, "statement lambda" syntax can be used, such as :
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The type checking benefit is great - I just wanted to understand if there is additional capability which I have not recognized.
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Feb 2, 2011
I am using Regular Expression validator for a text box. The below is working fine.It is not performing validation when I enter values like 0000..001.How can I modify validation expression? But it would allow values like 100,...5000 i.e zeros after a number.
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Dec 10, 2010
I'm debugging some tricky generic List-based code in VS 2010 - lots of heirarchy-processing etc.. Of course lambda expressions and anonymous methods aren't permitted within the immediates window and I can't be doing with stepping thru the code in the usual way as I'm still trying to get my head around the hierarchies ...Can anyone suggest a workaround or an alternative tool?P.S. An aside - I can't seem to find a visual studio 2010 tag?
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Dec 1, 2010
I need some help in regular expression.I am validating the textbox text when updating the records.When i click the update button,the first 5 letters should be equal to CM000 or cm000.How to validate this using regular expression in asp.net. does anyone know validationexpression for this.
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Apr 17, 2010
I have a control that's bound to a list property. If I remove elements from that list using javascript and post, then the model gets updated, and the elements get removed.
Unless I remove all the items from the list. Then no names for that property go into the form data, and so the default model binder leaves the model's list untouched. This code from DefaultModelBinder.cs line 572 in the RTM sources makes it clear:
[Code]....
So how do I indicate to the model binder that I do want it to update the list and Ido want the list to be emptied?
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Mar 9, 2010
I was trying to implement a dynamic update of a dropdown list in an ASP.NET.MVC2 RC 2 view. My code didn't work. So, in order to verify my approach, I resorted to a published code, which supposedly should be correct: In the View:
<%= Html.DropDownList("Numbers",(IEnumerable<SelectListItem>)ViewData["Services"]) %>
<select id="Select1">
</select>
<input type="button" id="Button1" value="Fill By Array" />
<script language="javascript" type="text/javascript">
$(function() {
$("#Button1").click(function(e) {
e.preventDefault();
var data = [];
$.getJSON("/Home/GetListViaJson", null, function(data) {
data = $.map(data, function(item, a) {
return "<option value=" + item.Value + ">" + item.Text + "</option>";
});
$("#Select1").html(data.join(""));
});
});
});
</script>
In the Controller:
[HandleError]
public class HomeController : Controller
{
public ActionResult Index()
{
//ViewData["Message"] = "Welcome to ASP.NET MVC!";
ViewData["Numbers"] = GenerateNumbers();
return View("Index");
}
[AcceptVerbs(HttpVerbs.Get)]
public JsonResult GetListViaJson()
{
return Json(GenerateNumbers());
}
private static List<SelectListItem> GenerateNumbers()
{
var numbers = (from p in Enumerable.Range(0, 20)
select new SelectListItem
{
Text = p.ToString(),
Value = p.ToString()
});
return numbers.ToList();
}
public ActionResult About()
{
return View();
}
}
The Html.DropDownList was correctly populated on PageLoad() event. But the GetListViaJson() action method, when called on the button event, did not update the "Select1" element. how to solve this update problem.
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