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• LINQ Query using Multiple From and Multiple Collections

  1: using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Text; 5:  6: namespace ConsoleApplication2 7: { 8: class Program 9: { 10: static void Main(string[] args) 11: { 12: var emps = GetEmployees(); 13: var deps = GetDepartments(); 14:  15: var results = from e in emps 16: from d in deps 17: where e.EmpNo >= 1 && d.DeptNo <= 30 18: select new { Emp = e, Dept = d }; 19: 20: foreach (var item in results) 21: { 22: Console.WriteLine("{0},{1},{2},{3}", item.Dept.DeptNo, item.Dept.DName, item.Emp.EmpNo, item.Emp.EmpName); 23: } 24: } 25:  26: private static List<Emp> GetEmployees() 27: { 28: return new List<Emp>() { 29: new Emp() { EmpNo = 1, EmpName = "Smith", DeptNo = 10 }, 30: new Emp() { EmpNo = 2, EmpName = "Narayan", DeptNo = 20 }, 31: new Emp() { EmpNo = 3, EmpName = "Rishi", DeptNo = 30 }, 32: new Emp() { EmpNo = 4, EmpName = "Guru", DeptNo = 10 }, 33: new Emp() { EmpNo = 5, EmpName = "Priya", DeptNo = 20 }, 34: new Emp() { EmpNo = 6, EmpName = "Riya", DeptNo = 10 } 35: }; 36: } 37:  38: private static List<Department> GetDepartments() 39: { 40: return new List<Department>() { 41: new Department() { DeptNo=10, DName="Accounts" }, 42: new Department() { DeptNo=20, DName="Finance" }, 43: new Department() { DeptNo=30, DName="Travel" } 44: }; 45: } 46: } 47:  48: class Emp 49: { 50: public int EmpNo { get; set; } 51: public string EmpName { get; set; } 52: public int DeptNo { get; set; } 53: } 54:  55: class Department 56: { 57: public int DeptNo { get; set; } 58: public String DName { get; set; } 59: } 60: } span.fullpost {display:none;}

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• How can I stop an auto-generated Linq to SQL class from loading ALL data?

  - by Gary McGill

  I have an ASP.NET MVC project, much like the NerdDinner tutorial example. (I'm using MVC 2, but followed the NerdDinner tutorial in order to create it). As per the instructions in part 3 of the tutorial, I've created a Linq-to-SQL model of my database by creating a "Linq to SQL Classes" (.dbml) surface, and dropping my database tables onto it. The designer has automatically added relationships between the generated classes based on my database tables. Let's say that my classes are as per the NerdDinner example, so I have Dinner and RSVP tables, where each Dinner record is associated with many RSVP records - hence in the generated classes, the Dinner object has a RSVPs property which is a list of RSVP objects. My problem is this: it appears (and I'd be gladly proved wrong on this) that as soon as I access a Dinner object, it's loading all of the corresponding RSVP objects, even if I don't use the RSVPs member. First question: is this really the default behavior for the generated classes? In my particular situation, the object graph contains many more tables (which have an order of magnitude more records), and so this is disastrous behaviour - I'd be loading tons of data when all I want to do is show the details of a single parent record. Second question: are there any properties exposed through the designer UI that would let me modify this behavior? (I can't find any). Third question: I've seen a description of how to control the loading of related records in a DataContext by using a DataShape object associated with the DataContext. Is that what I'm meant to do, and if so are there any tutorials like the NerdDinner one that would show not only how to do it, but also suggest a 'pattern' for normal use?

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• Get correct output from UTF-8 stored in VarChar using Entity Framework or Linq2SQL?

  - by jasonpenny

  Borland StarTeam seems to store its data as UTF-8 encoded data in VarChar fields. I have an ASP.NET MVC site that returns some custom HTML reports using the StarTeam database, and I would like to find a better solution for getting the correct data, for a rewrite with MVC2. I tried a few things with Encoding GetBytes and GetString, but I couldn't get it to work (we use mostly Delphi at work); then I figured out a T-SQL function to return a NVarChar from UTF-8 stored in a VarChar, and created new SQL views which return the data as NVarChar, but it's slow. The actual problem appears like this: “description†instead of “description”, in both SSMS and in a webpage when using Linq2SQL Is there a way to get the proper data out of these fields using Entity Framework or Linq2SQL?

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• How can I remove an "ALMOST" Duplicate using LINQ? ( OR SQL? )

  - by Atomiton

  This should be and easy one for the LINQ gurus out there. I'm doing a complex Query using UNIONS and CONTAINSTABLE in my database to return ranked results to my application. I'm getting duplicates in my returned data. This is expected. I'm using CONTAINSTABLE and CONTAINS to get all the results I need. CONTAINSTABLE is ranked by SQL and CONTAINS (which is run only on the Keywords field ) is hard-code-ranked by me. ( Sorry if that doesn't make sense ) Anyway, because the tuples aren't identical ( their rank is different ) a duplicate is returned. I figure the best way to deal with this is use LINQ. I know I'll be using the Distinct() extension method, but do I have to implement the IEqualityComparer interface? I'm a little fuzzy on how to do this. For argument's sake, say my resultset is structured like this class: class Content { ContentID int //KEY Rank int Description String } If I have a List<Content> how would I write the Distinct() method to exclude Rank? Ideally I'd like to keep the Content's highest Rank. SO, if one Content's RAnk is 112 and the other is 76. I'd like to keep the 112 rank. Hopefully I've given enough information.

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• Query data using LINQ to SQL and Entity Framework with foreign key? (Help me please)

  - by The Wind

  Hello! There is a problem I need help with your query on the data using LINQ to SQL and Entity Framework (I'm using Visual Studio 2010). My picure here: http://img.tamtay.vn/files/photo2/2010/5/28/10/962/4bff3a3b_1093f58f_untitled-1.gif I have three tables: tbl NewsDetails tblNewsCategories tblNewsInCategories (See screen 1 in my picture) Now, I want to retrieve records in the tblNewsDetails table, with condition: CategoryId=1, as the following results: (See screen 2 in my picture) But NewsID and CategoryId in tblNewsInCategories table is two foreign key, I do not see them and I do not know how to use them in your code. My code has errors: (See screen 3 in my picture) Please help me. Thanks! (I am a new member, should not have the right to insert images)

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• What is the return type for a anonymous linq query select? What is the best way to send this data ba

  - by punkouter

  This is a basic question. I have the basic SL4/RIA project set up and I want to create a new method in the domain service and return some data from it. I am unsure the proper easiest way to do this.. Should I wrap it up in a ToList()? I am unclear how to handle this anonymous type that was create.. what is the easiest way to return this data? public IQueryable<ApplicationLog> GetApplicationLogsGrouped() { var x = from c in ObjectContext.ApplicationLogs let dt = c.LogDate group c by new { y = dt.Value.Year, m = dt.Value.Month, d = dt.Value.Day } into mygroup select new { aaa = mygroup.Key, ProductCount = mygroup.Count() }; return x; // return this.ObjectContext.ApplicationLogs.Where(r => r.ApplicationID < 50); } Cannot implicitly convert type 'System.Linq.IQueryable<AnonymousType#1>' to 'System.Linq.IQueryable<CapRep4.Web.ApplicationLog>'. An explicit conversion exists (are you missing a cast?) 58 20 CapRep4.Web

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• LINQ to SQL - Why can't you use a WHERE after an ORDER BY?

  - by MCS

  The following code: // select all orders var orders = from o in FoodOrders where o.STATUS = 1 order by o.ORDER_DATE descending select o; // if customer id is specified, only select orders from specific customer if (customerID!=null) { orders = orders.Where(o => customerID.Equals(o.CUSTOMER_ID)); } gives me the following error: Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Linq.IOrderedQueryable'. An explicit conversion exists (are you missing a cast?) I fixed the error by doing the sorting at the end: // select all orders var orders = from o in FoodOrders where o.STATUS = 1 select o; // if customer id is specified, only select orders from specific customer if (customerID!=null) { orders = orders.Where(o => customerID.Equals(o.CUSTOMER_ID)); } // I'm forced to do the ordering here orders = orders.OrderBy(o => o.ORDER_DATE).Reverse(); But I'm wondering why is this limitation in place? What's the reason the API was designed in such a way that you can't add a where constraint after using an order by operator?

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• How to model my database when using entity framework 4?

  - by Junior Ewing

  Trying to wrap my head around the best approach in modelling a database when we are using Entity Framework 4 as the ORM layer. We are going to use asp.net mvc 2 for the application. Is it worth trying to model using the class diagram modeller that comes with Visual Studio 2010 where you graphically configure your models into the EDMX file and then generate out the database structure? I have run into a bunch of non trivial issues and for complex many to many mappings or multi primary key entities the answer is not that obvious even after poking around a while with the tools. I figure its easy at this point to give up and start modelling the DB using real, working DB modelling tools and then try to generate out the EDMX from the database, rather than trying to do the model first approach.

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• How to add second JOIN clause in Linq To Sql?

  - by Refracted Paladin

  I am having a lot of trouble coming up with the Linq equivalent of this legacy stored procedure. The biggest hurdle is it doesn't seem to want to let me add a second 'clause' on the join with tblAddress. I am getting a Cannot resolve method... error. Can anyone point out what I am doing wrong? Below is, first, the SPROC I need to convert and, second, my LINQ attempt so far; which is FULL OF FAIL! Thanks SELECT dbo.tblPersonInsuranceCoverage.PersonInsuranceCoverageID, dbo.tblPersonInsuranceCoverage.EffectiveDate, dbo.tblPersonInsuranceCoverage.ExpirationDate, dbo.tblPersonInsuranceCoverage.Priority, dbo.tblAdminInsuranceCompanyType.TypeName AS CoverageCategory, dbo.tblBusiness.BusinessName, dbo.tblAdminInsuranceType.TypeName AS TypeName, CASE WHEN dbo.tblAddress.AddressLine1 IS NULL THEN '' ELSE dbo.tblAddress.AddressLine1 END + ' ' + CASE WHEN dbo.tblAddress.CityName IS NULL THEN '' ELSE '<BR>' + dbo.tblAddress.CityName END + ' ' + CASE WHEN dbo.tblAddress.StateID IS NULL THEN '' WHEN dbo.tblAddress.StateID = 'ns' THEN '' ELSE dbo.tblAddress.StateID END AS Address FROM dbo.tblPersonInsuranceCoverage LEFT OUTER JOIN dbo.tblInsuranceCompany ON dbo.tblPersonInsuranceCoverage.InsuranceCompanyID = dbo.tblInsuranceCompany.InsuranceCompanyID LEFT OUTER JOIN dbo.tblBusiness ON dbo.tblBusiness.BusinessID = dbo.tblInsuranceCompany.BusinessID LEFT OUTER JOIN dbo.tblAddress ON dbo.tblAddress.BusinessID = dbo.tblBusiness.BusinessID and tblAddress.AddressTypeID = 'b' LEFT OUTER JOIN dbo.tblAdminInsuranceCompanyType ON dbo.tblPersonInsuranceCoverage.InsuranceCompanyTypeID = dbo.tblAdminInsuranceCompanyType.InsuranceCompanyTypeID LEFT OUTER JOIN dbo.tblAdminInsuranceType ON dbo.tblPersonInsuranceCoverage.InsuranceTypeID = dbo.tblAdminInsuranceType.InsuranceTypeID WHERE tblPersonInsuranceCoverage.PersonID = @PersonID var coverage = from insuranceCoverage in context.tblPersonInsuranceCoverages where insuranceCoverage.PersonID == personID join insuranceCompany in context.tblInsuranceCompanies on insuranceCoverage.InsuranceCompanyID equals insuranceCompany.InsuranceCompanyID join address in context.tblAddresses on insuranceCompany.tblBusiness.BusinessID equals address.BusinessID where address.AddressTypeID = 'b' select new { insuranceCoverage.PersonInsuranceCoverageID, insuranceCoverage.EffectiveDate, insuranceCoverage.ExpirationDate, insuranceCoverage.Priority, CoverageCategory = insuranceCompany.tblAdminInsuranceCompanyType.TypeName, insuranceCompany.tblBusiness.BusinessName, TypeName = insuranceCoverage.InsuranceTypeID, Address = };

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• Entity Framework 4 - Handling very large (1000+ tables) data models?

  - by David Kreps

  We've got a database with over 1000+ tables and would like to consider using EF4 for our data access layer, but I'm concerned about the practical realities of using it for such a large data model. I've seen this question and read about the suggested solutions here and here. These may work, but appear to refer to the first version of the Entity Framework (and are more complex than I'd like). Does anyone know if these solutions have been improved upon in EF4? Or have other suggestions all together? Thanks.

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• C# / Entity Framework / Linq question regarding calling a method when a class is accessed...

  - by Daniel

  So this is probably really basic, but I'm fairly new to all this. I am using Entity Framework with POCO entities. I want to call a method when a class property is set. I am trying to build an advertisement platform. I have a Customer class, a Venue class and an Advertisement class. I have my indexes set up in such a way that I can call customer.venue. However, I want to be able to call Customer.Venue.CurrentAdvertisement and have it execute a method (if CurrentAdvertisement is null) and return the current advertisement. I know I can explicitly set it every time, but I want to be able to override my classes so that whenever the CurrentAdvertisement property is accessed via LINQ it runs that method to return an ad. In order to do this I need to pass the Venue class a variable (venue name).

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• How can I use a compound condition in a join in Linq?

  - by Gary McGill

  Let's say I have a Customer table which has a PrimaryContactId field and a SecondaryContactId field. Both of these are foreign keys that reference the Contact table. For any given customer, either one or two contacts may be stored. In other words, PrimaryContactId can never be NULL, but SecondaryContactId can be NULL. If I drop my Customer and Contact tables onto the "Linq to SQL Classes" design surface, the class builder will spot the two FK relationships from the Customer table to the Contact table, and so the generated Customer class will have a Contact field and a Contact1 field (which I can rename to PrimaryContact and SecondaryContact to avoid confusion). Now suppose that I want to get details of all the contacts for a given set of customers. If there was always exactly one contact then I could write something like: from customer in customers join contact in contacts on customer.PrimaryContactId equals contact.id select ... ...which would be translated into something like: SELECT ... FROM Customer INNER JOIN Contact ON Customer.FirstSalesPersonId = Contact.id But, because I want to join on both the contact fields, I want the SQL to look something like: SELECT ... FROM Customer INNER JOIN Contact ON Customer.FirstSalesPersonId = Contact.id OR Customer.SecondSalesPersonId = Contact.id How can I write a Linq expression to do that?

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• How do I add a where filter using the original Linq-to-SQL object in the following scenario

  - by GenericTypeTea

  I am performing a select query using the following Linq expression: Table<Tbl_Movement> movements = context.Tbl_Movement; var query = from m in movements select new MovementSummary { Id = m.DocketId, Created = m.DateTimeStamp, CreatedBy = m.Tbl_User.FullName, DocketNumber = m.DocketNumber, DocketTypeDescription = m.Ref_DocketType.DocketType, DocketTypeId = m.DocketTypeId, Site = new Site() { Id = m.Tbl_Site.SiteId, FirstLine = m.Tbl_Site.FirstLine, Postcode = m.Tbl_Site.Postcode, SiteName = m.Tbl_Site.SiteName, TownCity = m.Tbl_Site.TownCity, Brewery = new Brewery() { Id = m.Tbl_Site.Ref_Brewery.BreweryId, BreweryName = m.Tbl_Site.Ref_Brewery.BreweryName }, Region = new Region() { Description = m.Tbl_Site.Ref_Region.Description, Id = m.Tbl_Site.Ref_Region.RegionId } } }; I am also passing in an IFilter class into the method where this select is performed. public interface IJobFilter { int? PersonId { get; set; } int? RegionId { get; set; } int? SiteId { get; set; } int? AssetId { get; set; } } How do I add these where parameters into my SQL expression? Preferably I'd like this done in another method as the filtering will be re-used across multiple repositories. Unfortunately when I do query.Where it has become an IQueryable<MovementSummary>. I'm assuming it has become this as I'm returning an IEnumerable<MovementSummary>. I've only just started learning LINQ, so be gentle.

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• Why are my bound parameters all identical (using Linq)?

  - by Scott Stafford

  When I run this snippet of code: string[] words = new string[] { "foo", "bar" }; var results = from row in Assets select row; foreach (string word in words) { results = results.Where(row => row.Name.Contains(word)); } I get this SQL: -- Region Parameters DECLARE @p0 VarChar(5) = '%bar%' DECLARE @p1 VarChar(5) = '%bar%' -- EndRegion SELECT ... FROM [Assets] AS [t0] WHERE ([t0].[Name] LIKE @p0) AND ([t0].[Name] LIKE @p1) Note that @p0 and @p1 are both bar, when I wanted them to be foo and bar. I guess Linq is somehow binding a reference to the variable word rather than a reference to the string currently referenced by word? What is the best way to avoid this problem? (Also, if you have any suggestions for a better title for this question, please put it in the comments.) Note that I tried this with regular Linq also, with the same results (you can paste this right into Linqpad): string[] words = new string[] { "f", "a" }; string[] dictionary = new string[] { "foo", "bar", "jack", "splat" }; var results = from row in dictionary select row; foreach (string word in words) { results = results.Where(row => row.Contains(word)); } results.Dump(); Dumps: bar jack splat

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• How do I delete an object from an Entity Framework model without first loading it?

  - by Tomas Lycken

  I am quite sure I've seen the answer to this question somewhere, but as I couldn't find it with a couple of searches on SO or google, I ask it again anyway... In Entity Framework, the only way to delete a data object seems to be MyEntityModel ent = new MyEntityModel(); ent.DeleteObject(theObjectToDelete); ent.SaveChanges(); However, this approach requires the object to be loaded to, in this case, the Controller first, just to delete it. Is there a way to delete a business object referencing only for instance its ID? If there is a smarter way using Linq or Lambda expressions, that is fine too. The main objective, though, is to avoid loading data just to delete it.

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• Obstacle Avoidance steering behavior: how can an entity avoid an obstacle while other forces are acting on the entity?

  - by Prog

  I'm trying to implement the Obstacle Avoidance steering behavior in my 2D game. Currently my approach is to apply a force on the entity, in the direction of the normal of the heading, scaled by a number that gets bigger the closer we are to the obstacle. This is supposed to push the entity to the side and avoid the obstacle that blocks it's way. However, in the same time that my entity tries to avoid an obstacle, it Seeks to a point more or less behind the obstacle (which is the reason it needs to avoid the obstacle in the first place). The Seek algorithm constantly applies a force on the entity that pushes it (more or less) in the direction of the obstacle, while the Obstacle Avoidance algorithm constantly applies a force that pushes the entity away (more accurately, to the side) of the obstacle. The result is that sometimes the entity succesfully avoids the obstacle, and sometimes it collides with it, depending on the strength of the avoidance force I'm applying. How can I make sure that a force will succeed in steering the entity in some direction, while other forces are currently acting on the entity? (And while still looking natural). I can't allow entities to collide with obstacles when realistically they should be able to easily avoid them, doesn't matter what they're currently doing. Also, the Obstacle Avoidance algorithm is made exactly for the case where another force is acting on the entity. Otherwise it wouldn't be moving and there would be no need to avoid anything. So maybe I'm missing something. Thanks

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• What micro web-framework has the lowest overhead but includes templating

  - by Simon Martin

  I want to rewrite a simple small (10 page) website and besides a contact form it could be written in pure html. It is currently built with classic asp and Dreamweaver templates. The reason I'm not simply writing 10 html pages is that I want to keep the layout all in 1 place so would need either includes or a masterpage. I don't want to use Dreamweaver templates, or batch processing (like org-mode) because I want to be able to edit using notepad (or Visual Studio) because occasionally I might need to edit a file on the server (Go Daddy's IIS admin interface will let me edit text). I don't want to use ASP.NET MVC or WebForms (which I use in my day job) because I don't need all the overhead they bring with them when essentially I'm serving up 9 static files, 1 contact form and 1 list of clubs (that I aim to use jQuery to filter). The shared hosting package I have on Go Daddy seems to take a long time to spin up when serving aspx files. Currently the clubs page is driven from an MS SQL database that I try to keep up to date by manually checking the dojo locator on the main HQ pages and editing the entries myself, this is again way over the top. I aim to get a text file with the club details (probably in JSON or xml format) and use that as the source for the clubs page. There will need to be a bit of programming for this as the HQ site is unable to provide an extract / feed so something will have to scrape the site periodically to update my clubs persistence file. I'd like that to be automated - but I'm happy to have that triggered on a visit to the clubs page so I don't need to worry about scheduling a job. I would probably have a separate process that updates the persistence that has nothing to do with the rest of the site. Ideally I'd like to use Mercurial (or git) to publish, I know Bitbucket (and github) both serve static page sites so they wouldn't work in this scenario (dynamic pages and a contact form) but that's the model I'd like to use if there is such a thing. My requirements are: Simple templating system, 1 place to define header, footers, menu etc., that can be edited using just notepad. Very minimal / lightweight framework. I don't need a monster for 10 pages Must run either on IIS7 (shared Go Daddy Windows hosting) or other free host

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• Reading XML element & child nodes using LINQ in Vb.net- help me in where condition :(

  - by New Linq Baby

  Hi, I am new in LINQ world. I need an urgent help in reading the xml elements using LINQ with specific where condition. I need to find the max air_temp for a county i.e where county name = "Boone" and hour id = "06/03/2009 09:00CDT" i tried something like below, but no luck : Dim custs As IEnumerable = From c In Element.Load("C:\meridian.xml").Elements("county") _ Select c.Elements("hour").Elements("air_temp").Max() For Each x In custs Response.Write(custs(0).ToString()) Next ------------------- here is the xml file : <forecasts> <issued>06/02/2009 12:00CDT</issued> - <county name="Adair"> - <hour id="06/02/2009 12:00CDT"> <air_temp>61</air_temp> <cloud_cover>overcast</cloud_cover> <dew_point>59</dew_point> <precip_prob>90</precip_prob> <precip_rate>0.12</precip_rate> <precip_type>rain</precip_type> <snow_rate>0.0</snow_rate> <wind_direction>NE</wind_direction> <wind_speed>12</wind_speed> <dew_point_confidence>-3/+3</dew_point_confidence> <road_temp>64</road_temp> <road_frost_prob>0</road_frost_prob> <road_potential_evap_rate>429</road_potential_evap_rate> <road_temp_confidence>-3/+2</road_temp_confidence> <dew_point_confidence>-3/+3</dew_point_confidence> <bridge_temp>63</bridge_temp> <bridge_temp_confidence>-4/+2</bridge_temp_confidence> <bridge_frost>NO</bridge_frost> </hour> - <hour id="06/02/2009 13:00CDT"> <air_temp>61</air_temp> <cloud_cover>overcast</cloud_cover> <dew_point>60</dew_point> <precip_prob>70</precip_prob> <precip_rate>0.01</precip_rate> <precip_type>rain</precip_type> <snow_rate>0.0</snow_rate> <wind_direction>ENE</wind_direction> <wind_speed>10</wind_speed> <dew_point_confidence>-3/+3</dew_point_confidence> <road_temp>65</road_temp> <road_frost_prob>0</road_frost_prob> <road_potential_evap_rate>411</road_potential_evap_rate> <road_temp_confidence>-3/+2</road_temp_confidence> <dew_point_confidence>-3/+3</dew_point_confidence> <bridge_temp>64</bridge_temp> <bridge_temp_confidence>-4/+1</bridge_temp_confidence> <bridge_frost>NO</bridge_frost> </hour>

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• How do I add ROW_NUMBER to a LINQ query or Entity?

  - by Whozumommy

  I'm stumped by this easy data problem. I'm using the Entity framework and have a database of products. My results page returns a paginated list of these products. Right now my results are ordered by the number of sales of each product, so my code looks like this: return Products.OrderByDescending(u => u.Sales.Count()); This returns an IQueryable dataset of my entities, sorted by the number of sales. I want my results page to show the rank of each product (in the dataset). My results should look like this: Page #1 1. Bananas 2. Apples 3. Coffee Page #2 4. Cookies 5. Ice Cream 6. Lettuce I'm expecting that I just want to add a column in my results using the SQL ROW_NUMBER variable...but I don't know how to add this column to my results datatable. My resulting page does contain a foreach loop, but since I'm using a paginated set I'm guessing using that number to fake a ranking number would NOT be the best approach. So my question is, how do I add a ROW_NUMBER column to my query results in this case?

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• Can I use the auto-generated Linq-to-SQL entity classes in 'disconnected' mode?

  - by Gary McGill

  Suppose I have an automatically-generated Employee class based on the Employees table in my database. Now suppose that I want to pass employee data to a ShowAges method that will print out name & age for a list of employees. I'll retrieve the data for a given set of employees via a linq query, which will return me a set of Employee instances. I can then pass the Employee instances to the ShowAges method, which can access the Name & Age fields to get the data it needs. However, because my Employees table has relationships with various other tables in my database, my Employee class also has a Department field, a Manager field, etc. that provide access to related records in those other tables. If the ShowAges method were to invoke any of those methods, this would cause lots more data to be fetched from the database, on-demand. I want to be sure that the ShowAges method only uses the data I have already fetched for it, but I really don't want to have to go to the trouble of defining a new class which replicates the Employee class but has fewer methods. (In my real-world scenario, the class would have to be considerably more complex than the Employee class described here; it would have several 'joined' classes that do need to be populated, and others that don't). Is there a way to 'switch off' or 'disconnect' the Employees instances so that an attempt to access any property or related object that's not already populated will raise an exception? If not, then I assume that since this must be a common requirement, there might be an already-established pattern for doing this sort of thing?

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• What is the best way in assigning foreign key when using entity framework & LINQ to Entities?

  - by Abdel Olakara

  Hi all, I need to know the best practice of creating an entity object and assigning the foreign key. Here is my scenario. I have a Product table with pid,name,unit_price etc.. I also have a Rating table with pid (foregin key),rate,votes etc... Currently i am doing the following to create the rating object: var prod = entities.Product.First(p => p.product_id == pid); prod.Rating.Load(); if (prod.Rating != null) { log.Info("Rating already exists!"); // set values and Calcuate the score } else { log.Info("New Rating!!!"); Rating rating = new Rating(); // set values and do inital calculation prod.Rating = rating; } entities.SaveChanges(); Even though this works fine, i would like to know the best practice in doing these kind of assignment. Thanks for your suggestions and info. Best Regards, Abdel Olakara

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• 2-Way databinding with Entity Framework and WPF DataGrid , is Possible ?

  - by Panindra

  i am working on POS application using SQL CE , WPF , Entity framework 3.5sp2 and iam trying to use data grid as my Order Entry Control for User to enter Products Order . Iam plannning to bind this to enitiy frmae work model , abd looking for 2 way updating ? private void button1_Click(object sender, RoutedEventArgs e) { using (MasterEntities nwEntities = new MasterEntities()) { var users = from d in nwEntities.Companies select new { d.CompanyId, d.CompanyName, d.Place }; listBox1.DataContext = users; dataGrid1.DataContext = users; // foreach (String c in customers) // { // MessageBox.Show(c.ToString()); // } } } When try to double clikc on the datagrid it through s a error with Caption " Invalid Operation Execption was unhandled " and Message " A TwoWay or OneWayToSource binding cannot work on the read-only property 'CompanyId' of type '<f__AnonymousType0`3[System.Int32,System.String,System.String]'. whats wrong here and my xaml coding goes like this <Grid> <ListBox Name="listBox1" ItemsSource="{Binding}" /> <Button Content="Show " Name="button1" Click="button1_Click" /> <DataGrid AutoGenerateColumns="False" Name="dataGrid1" ItemsSource="{Binding}" > <DataGrid.Columns> <DataGridTextColumn Header=" ID" Binding="{Binding CompanyId}"/> <DataGridTextColumn Header="Company Name" Binding="{Binding CompanyName}"/> <DataGridTextColumn Header="Place" Binding="{Binding Place}" /> </DataGrid.Columns> </DataGrid> </Grid> EDITED : i made the changes shown by @vorrtex, But, then i added another button to save the chages and in button click event i added follwing code , butit showing Updating error private void button2_Click(object sender, RoutedEventArgs e) { nwEntities.SaveChanges(); }

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• A question about entities, roles and interfaces in Entity Framework 4.

  - by mvole

  Hi, I am an experienced .NET developer but new to EF - so please bear with me. I will use an example of a college application to illustrate my problem. I have these user roles: Lecturer, Student, Administrator. In my code I envisage working with these entities as distinct classes so e.g. a Lecturer teaches a collection of Students. And work with 'is Student' 'TypeOf' etc. Each of these entities share lots of common properties/methods e.g. they can all log onto the system and do stuff related to their role. In EF designer I can create a base entity Person (or User...) and have Lecturer, Student and Administrator all inherit from that. The difficulty I have is that a Lecturer can be an Administrator - and in fact on occasion a Student can be a Lecturer. If I were to add other entities such as Employee and Warden then this gets even more of an issue. I could presumably work with Interfaces so a person could implement ILecturer and IStudent, however I do not see how this fits within EF. I would like to work within the EF designer if possible and I'm working model-first (coding in C#). So any help and advice/samples would be very welcome and much appreciated. Thanks

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• Error: FormatException was unhandled by user code in Linq how to solve?

  - by programmerist

  Look please below this codes throw me : FormatException was unhandled by user code Codes: satis.KDV = Decimal.Parse((from o in genSatisctx.Urun where o.ID == UrunID select o.Kdv).ToString()); How can i rewrite linq query?

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• C# Use Linq to Extract a single XML attribute for each XML file in a directory.

  - by guazz

  Hi all, How do I use Linq to extract a single XML attribute form each XML file in a directory and put that element in a C# list. Do I have to loop thru each file one-by-one? The XML files are quite large so I'd like to do this without loading the entire file into memory. Thanks, j

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