I Use entity framework 4.
Here is my model
Language
LangID
LangName
Product
PrdID
IsActive
ProductText
PrdID
LangID
Text
Category
CatID
IsActive
CategoryText
CatID
LangID
Text
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.?
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);
i have the following, which works:
@{Html.RenderAction("Detail", "Help", new { pageName = "press" });}
But instead i'd like to use a lambda expression to get away from the string bits. I tried using the following (which is the nearest approximation i could figure based on my limited knowledge of the engine):
@{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
However, i'm reading in the Apress MVC 2.0 book that it is in fact declared as a method that takes type arguments. Am i missing an assembly reference, or has it not been included in the MVC 3.0 Preview 1 build?
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();
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
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.
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.
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.
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")
.Descendants("MMMS")
.Where(a => a.Attribute("ID").Value == MID)
.SelectMany(b => b.Descendants("ABC")).Count();
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.
What will be the equivalent GroupJoin lambda expression in LINQ when I do this.
Dim fruit_salad = (From fruits In _DataContext_Fruits _
Group Join fruitRipe In _DataContext_FruitRipe On fruitRipe.fID Equals fruits.fID Into Group
From fruitty_lecious In Group.DefaultIfEmpty() _
[code]...
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
What s the best way to implement a method that creates and assings ID s to user on a asp.net application?
I was thinking about using DateTime ticks and thread id
I wanna make sure that there is no collision and user ids are unique.
ID can be a string or long.
should i use MD5 on some information that i collect from user? what would that be?
I have seen that md5 collision rate is very low.
How can I create generic class from System.Web.Mvc.ViewPage?
View 1 RepliesI want to create a generic web.config file for different web servers in VB.NET. So, depending on the server configuration requirements, applications can retrieve all values from that generic configuration file.
Is this possible? How would I do this?
I am currently binding a Nullable bit column to a listview control. When you declare a list view item I need to handle the case when the null value is used instead of just true or false.
<asp:Checkbox ID="Chk1" runat="server"
Checked='<%# HandleNullableBool(Eval("IsUsed")) %>' />
Then in the page I add a HandleNullableBool() function inside the ASPX page.
protected static bool HandleNullableBool(object value)
{
return (value == null) ? false : (bool)value;
}
This works fine but I need to use this in several pages so I tried creating a utility class with a static HandleNullableBool. But using it in the asp page does not work. Is there a way to do this in another class instead of the ASPX page?
<asp:Checkbox ID="Chk1" runat="server"
Checked='<%# Util.HandleNullableBool(Eval("IsUsed")) %>' />
I'm currently facing a performance problem with creating POCO objects from my database. I'm using Entity Framework 4 as OR-Mapper. The whole application is a prototype for now. Let's assume I want to have some business objects like classes 'Printer' or 'Scanner'. Both classes inherit from a BaseClass called Product.
The business classes exist.
I try to use a more generic database approach. I don't want to create tables for "Printer" nor "Scanner". I want to have 3 tables: One called Product, and the other Property and PropertyValue (which stores all assigned values to a specific Product). In my business layer I do create a specific object like this:
public Printer GetPrinter(int IDProduct)
{
Printer item = new Printer();
// get the product object with EF
// get all PropertyValues
// (with Reflection) foreach property in item.GetType().GetProperties
// {
// property.SetValue("specific value")
// }
return item;
}
This is how the EF model looks like: Works fine so far. For now I'm doing performance tests for retrieving multiple sets. I've created a prototype and improved it several times to increase the performance. It is still far away from being usable. I takes 919ms to create 300 objects who only contain 3 properties. The reason for choosing such DB design is to have a generic database design. Adding new properties should only be done in the business model.
Am I just being too stupid to create a performant way of retrieving xx objects or is my approach totally wrong? As far as I understand OR-Mapper, they are basically doing the same?
Is something like the below possible?
public static T Sum<T>(this DataTable dt, string columnName)
where T : IEnumerable<decimal>, IComparable<decimal>[code]....
It feels like i'm almost there, but not quite :/
Just trying to sum up either decimal or int values in a column in datatable. Currently getting a compile error, however think this is due to the incorrect generic constraint.
I am trying to create a User Control that accepts a generic List of CustomObject as a bindable property.
I'd like it to look a little somthing like this :
TabularReport.ascx
[Bindable (true)]
public IList<T> Source
{
get;
set;
}
protected void Page_Load(object sender, EventArgs e).........
i am creating an form which have several text box and i used regular expression validator which will check the text of text box is in only alphabets.
now any budy can tell me validation expression for this case.
or where i'll get useful information about create validation expression .
I want to create Regular Expression for phone number and valid digits allowed are (,),-,+,0----9. If the left bracket ( is there,then its necessay that right bracket is also there. How to create the Regular Expression for the above. I dont know how to create the regular Expression,
View 4 RepliesI want to extract some keywords out of a query string for a search application in asp.net.I decoded the url string first, so it's plain textI have this to start with, but I want to add a keyword group
([?&])q=[^&]+[&]?
I get this ?q=harbour landing dental&I'd like to trim off the stuff for pure words, but not sure if that's possibleI also have a long list of possible query string value fields that I want to check against
?q=
@q=
?qs=
&qs=
I'm having a TextBox and it can be accept only the string like "49=N,38=S,56=S,......"
so can u tell me how can i create my regular expression for validate above string.
How would I create a regular expression validator for a textbox, to limit the input to a decimal number between .1 and 1?
View 1 Replieswhat regular expression should i use to validate cricket overs in textbox. like it can be 5.1, 5.2,5.3,5.4,5.5 but it should not contain fraction value greater than .5 ,also the values should be numeric only (float and int)
View 3 RepliesI need a way to create a regular expression from a string or an array of domain names. for example string array = [URL]. Once I click save I would want to create a regular expression that would match all 3 with or without '.com' extension. Then Another task would be to pull this data out of regular expression and put it back into an array.
View 5 Replies
