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  • C# Joins/Where with Linq and Lambda

    - by David
    Hello, I'm having trouble with a query written in Linq and Lambda. So far, I'm getting allot of errors here's my code: int id = 1; var query = database.Posts.Join(database.Post_Metas, post => database.Posts.Where(x => x.ID == id), meta => database.Post_Metas.Where(x => x.Post_ID == id), (post, meta) => new { Post = post, Meta = meta }); I'm new to using Linq, so I'm not sure if this query is correct.

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  • Linq like or other construction

    - by Yauhen Kavalenka
    I have DB oracle in my solution. I want to have some results in this query. Query example: select * from doctor where doctor.name like '%IVANOV_A%'; But if i do it at LINQ i cannot get any result. from p in repository.Doctor.Where(x => x.Name.ToLower().Containsname)) select p; Where 'name' is variable of string parameter. Web layout request next string: "Ivanov a" or "A Ivanov" But i suggest for user choose you pattetn for query. How i can to get "patient by name" if name consist of "First name" and "Last name" but user doesn't know your doctor's full name?

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  • linq NullReferenceException while checking for null reference

    - by Odrade
    I have the following LINQ query: List<FileInputItem> inputList = GetInputList(); var results = from FileInputItem f in inputList where ( Path.GetDirectoryName(f.Folder).ToLower().Trim() == somePath || Path.GetDirectoryName(f.Folder).ToLower().Trim() == someOtherPath ) && f.Expression == null select f; Every time this query is executed, it generates a NullReferenceException. If I remove the condition f.Expression == null or change it to f.Expression != null, the query executes normally (giving the wrong results, of course). The relevant bits of FileInputItem look like this: [Serializable] public class FileInputItem { [XmlElement("Folder")] public string Folder { get; set; } [XmlElement("Expression")] public string Expression { get; set; } /*SNIP. Irrelevant properties */ } I'm new to LINQ to objects, so I'm probably missing something fundamental here. What's the deal?

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  • Hos to group the complex list objects by using Linq

    - by Daoming Yang
    I want to select and group the products, and rank them by the number of times they occur. For example, I have an OrderList each of order object has a OrderProductVariantList(OrderLineList), and each of OrderProductVariant object has ProductVariant, and then the ProductVariant object will have a Product object which contains product information. A friend helped me with the following code. It could be compiled, but it did not return any value/result. I used the watch window for the query and it gave me "The name 'query' does not exist in the current context". Can anyone help me? Many thanks. var query = orderList.SelectMany( o => o.OrderLineList ) // results in IEnumerable<OrderProductVariant> .Select( opv => opv.ProductVariant ) .Select( pv => p.Product ) .GroupBy( p => p ) .Select( g => new { Product = g.Key, Count = g.Count() });

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  • Left outer join null using VB.NET and LINQ

    - by jvcoach23
    I've got what I think is a working left outer join LINQ query, but I'm having problems with the select because of null values in the right hand side of the join. Here is what I have so far Dim Os = From e In oExcel Group Join c In oClassIndexS On c.tClassCode Equals Mid(e.ClassCode, 1, 4) Into right1 = Group _ From c In right1.DefaultIfEmpty I want to return all of e and one column from c called tClassCode. I was wondering what the syntax would be. As you can see, I'm using VB.NET. Update... Here is the query doing join where I get the error: _message = "Object reference not set to an instance of an object." Dim Os = From e In oExcel Group Join c In oClassIndexS On c.tClassCode Equals Mid(e.ClassCode, 1, 4) Into right1 = Group _ From c In right1.DefaultIfEmpty Select e, c.tClassCode If I remove the c.tClassCode from the select, the query runs without error. So I thought perhaps I needed to do a select new, but I don't think I was doing that correctly either.

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  • How to optimize this Linq query

    - by Luke101
    I am trying to optimize this query. It is not slow for now but I am expecting a spike to hit this query in the near future. Is there anything else i can do to make this query faster? var posts = from p in context.post where p.post_isdeleted == false && p.post_parentid == null select new { p.post_date, p.post_id, p.post_titleslug, p.post_title, p.post_descriptionrender, p.userinfo.user_username, p.userinfo.user_userid, p.userinfo.user_GravatarHash, p.userinfo.user_points, p.category.catid, p.category.name, p.post_answercount, p.post_hasbestanswer, p.post_hits, p.post_isanonymous, p.post_votecount, FavoriteCount = context.favorites.Where(x => x.post.post_id == p.post_id).Count(), tags = from tg in context.posttag where tg.posttag_postid == p.post_id select new { tg.tag.tag_id, tg.tag.tag_title } };

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  • Create LINQ to entities OrderBy expression on the fly

    - by AyKarsi
    I'm trying to add the orderby expression on the fly. But when the query below is executed I get the following exception: System.NotSupportedException: Unable to create a constant value of type 'Closure type'. Only primitive types ('such as Int32, String, and Guid') are supported in this context. The strange thing is, I am query exactly those primitive types only. string sortBy = HttpContext.Current.Request.QueryString["sidx"]; ParameterExpression prm = Expression.Parameter(typeof(buskerPosting), "posting"); Expression orderByProperty = Expression.Property(prm, sortBy); // get the paged records IQueryable<PostingListItemDto> query = (from posting in be.buskerPosting where posting.buskerAccount.cmsMember.nodeId == m.Id orderby orderByProperty //orderby posting.Created select new PostingListItemDto { Set = posting }).Skip<PostingListItemDto>((page - 1) * pageSize).Take<PostingListItemDto>(pageSize); Hope somebody can shed some light on this!

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  • Removing values from a returned linq query

    - by Diver D
    HI there I am hoping for some help with a query I have. I have this query var group = from r in CustomerItem group r by r.StoreItemID into g select new { StoreItemID = g.Key, ItemCount = g.Count(), ItemAmount = Customer.Sum(cr => cr.ItemAmount),RedeemedAmount = Customer.Sum(x => x.RedeemedAmount) }; I am returning my results to a list so I can bind it listbox. I have a property called EntryType which is an int. There are 2 available numbers 1 or 2 Lets say I had 3 items that my query is working with 2 of them had the EntryType = 1 and the 3rd had EntryType2. The first records had a ItemAmount of 55.00 and the 3rd had a ItemAmount of 50.00 How can I group using something simlar to above but minus the ItemAmount of 50.00 from the grouped amount to return 60.00? Any help would be great!!

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  • Linq Query to IEnumerable<T> Extension Method

    - by CSharpNoob
    Consider this, class Item { public string ID { get; set;} public string Description { get; set; } } class SaleItem { public string ID { get; set;} public string Discount { get; set; } } var itemsToRemoved = (List<Item>)ViewState["ItemsToRemove"]; // get only rows of ID var query = from i in itemsToRemoved select i.ID; var saleItems= (List<SaleItem>)ViewState["SaleItems"]; foreach (string s in query.ToArray()) { saleItems.RemoveItem(s); } How can I write this LINQ phrase using IEnumerable/List Extension methods // get only rows of ID var query = from i in items select i.ID; thanks in advance.

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  • Select a Column Dynamically using LINQ?

    - by vsj
    Hi all I am trying to do a very simple dynamic query which will select a column dynamically I mean the selection of column would depend upon another query so I would select x col if cond1 and y if cond2 so I tried using query.Select(colname) using the extension method also tried using Func< but I am not sure how to go about this I have read about dynamic extension for linq and also reflection but woth reflection to the GetValue function does not return value for my column in database. please help me out I am jus trying to select a column dynamically at runtime and no condtions really on it.

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  • Linq Order By a subtable

    - by Michael
    Hello, My question is how to sort a Linq query by a sub table: Table Apps: - app_id - name Table AppStatus: - app_status_id - app_id - severity - status_date I would like to have a query with all the apps, sorted by the last status severity: app_id name 1 first 2 second 3 third app_status_id app_id severity status_date 1 1 5 12-4-2010 2 1 2 15-4-2010 3 2 7 10-4-2010 4 3 3 13-4-2010 Now i want it sorted like: app_id name 3 third 1 first 2 second Can anyone help me with a LINQ query for this. I tried the following already, but that didn't work: var apps = from apps in dc.Apps orderby apps.AppStatus.LastOrDefault().severity select apps;

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  • Linq to Datarow, Select multiple columns as distinct?

    - by Beta033
    basically i'm trying to reproduce the following mssql query as LINQ SELECT DISTINCT [TABLENAME], [COLUMNNAME] FROM [DATATABLE] the closest i've got is Dim query = (From row As DataRow In ds.Tables("DATATABLE").Rows _ Select row("COLUMNNAME") ,row("TABLENAME").Distinct when i do the above i get the error Range variable name can be inferred only from a simple or qualified name with no arguments. i was sort of expecting it to return a collection that i could then iterate through and perform actions for each entry. maybe a datarow collection? As a complete LINQ newb, i'm not sure what i'm missing. i've tried variations on Select new with { row("COLUMNNAME") ,row("TABLENAME")} and get: Anonymous type member name can be inferred only from a simple or qualified name with no arguments. Also, does anyone know of any good books/resources to get fluent?

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  • SQL Subquery in LINQ for Entity Framework 4.0

    - by Jorin
    I'm new to LINQ and EF, but I've been able to stumble through for the majority of the queries I have, but this one has me completely confused. No matter what I try, it comes up in SQL Profiler as a big mess :-). I have two tables: Users and UsersProjects. The goal of this query is to list all the users who are working on projects with the specified user. Here is the query as I have it written in SQL. It's a subquery, but I don't know of a way to simplify it further, but I'm open to suggestions there as well. SELECT DISTINCT Users.FirstName, Users.LastName FROM Users INNER JOIN UsersProjects ON Users.ID=UsersProjects.UserID WHERE UsersProjects.ProjectID IN (SELECT ProjectID FROM UsersProjects WHERE UserID=@UserID) Anybody able to help?? It seems like a fairly simple subquery in SQL, but in LINQ, I'm baffled. Thanks, Jorin

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  • Linq where clause with multiple conditions and null check

    - by SocialAddict
    I'm trying to check if a date is not null in linq and if it isn't check its a past date. QuestionnaireRepo.FindAll(q => !q.ExpiredDate.HasValue || q.ExpiredDate >DateTime.Now).OrderByDescending(order => order.CreatedDate); I need the second check to only apply if the first is true. I am using a single repository pattern and FindAll accepted a where clause ANy ideas? There are lots of similar questions on here but not that give the answer, I'm very new to Linq as you may of guessed :) Edit: I get the results I require now but it will be checking the conditional on null values in some cases. Is this not a bad thing?

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  • NullReferenceException when calling InsertOnSubmit in Linq to Sql.

    - by Charlie
    I'm trying to insert a new object into my database using LINQ to SQL but get a NullReferenceException when I call InsertOnSubmit() in the code snippet below. I'm passing in a derived class called FileUploadAudit, and all properties on the object are set. public void Save(Audit audit) { try { using (ULNDataClassesDataContext dataContext = this.Connection.GetContext()) { if (audit.AuditID > 0) { throw new RepositoryException(RepositoryExceptionCode.EntityAlreadyExists, string.Format("An audit entry with ID {0} already exists and cannot be updated.", audit.AuditID)); } dataContext.Audits.InsertOnSubmit(audit); dataContext.SubmitChanges(); } } catch (Exception ex) { if (ObjectFactory.GetInstance<IExceptionHandler>().HandleException(ex)) { throw; } } } Here's the stack trace: at System.Data.Linq.Table`1.InsertOnSubmit(TEntity entity) at XXXX.XXXX.Repository.AuditRepository.Save(Audit audit) C:\XXXX\AuditRepository.cs:line 25" I've added to the Audit class like this: public partial class Audit { public Audit(string message, ULNComponent component) : this() { this.Message = message; this.DateTimeRecorded = DateTime.Now; this.SetComponent(component); this.ServerName = Environment.MachineName; } public bool IsError { get; set; } public void SetComponent(ULNComponent component) { this.Component = Enum.GetName(typeof(ULNComponent), component); } } And the derived FileUploadAudit looks like this: public class FileUploadAudit : Audit { public FileUploadAudit(string message, ULNComponent component, Guid fileGuid, string originalFilename, string physicalFilename, HttpPostedFileBase postedFile) : base(message, component) { this.FileGuid = fileGuid; this.OriginalFilename = originalFilename; this.PhysicalFileName = physicalFilename; this.PostedFile = postedFile; this.ValidationErrors = new List<string>(); } public Guid FileGuid { get; set; } public string OriginalFilename { get; set; } public string PhysicalFileName { get; set; } public HttpPostedFileBase PostedFile { get; set; } public IList<string> ValidationErrors { get; set; } } Any ideas what the problem is? The closest question I could find to mine is here but my partial Audit class is calling the parameterless constructor in the generated code, and I still get the problem. UPDATE: This problem only occurs when I pass in the derived FileUploadAudit class, the Audit class works fine. The Audit class is generated as a linq to sql class and there are no Properties mapped to database fields in the derived class.

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  • C#: Delegate syntax?

    - by Rosarch
    I'm developing a game. I want to have game entities each have their own Damage() function. When called, they will calculate how much damage they want to do: public class CombatantGameModel : GameObjectModel { public int Health { get; set; } /// <summary> /// If the attack hits, how much damage does it do? /// </summary> /// <param name="randomSample">A random value from [0 .. 1]. Use to introduce randomness in the attack's damage.</param> /// <returns>The amount of damage the attack does</returns> public delegate int Damage(float randomSample); public CombatantGameModel(GameObjectController controller) : base(controller) {} } public class CombatantGameObject : GameObjectController { private new readonly CombatantGameModel model; public new virtual CombatantGameModel Model { get { return model; } } public CombatantGameObject() { model = new CombatantGameModel(this); } } However, when I try to call that method, I get a compiler error: /// <summary> /// Calculates the results of an attack, and directly updates the GameObjects involved. /// </summary> /// <param name="attacker">The aggressor GameObject</param> /// <param name="victim">The GameObject under assault</param> public void ComputeAttackUpdate(CombatantGameObject attacker, CombatantGameObject victim) { if (worldQuery.IsColliding(attacker, victim, false)) { victim.Model.Health -= attacker.Model.Damage((float) rand.NextDouble()); // error here Debug.WriteLine(String.Format("{0} hits {1} for {2} damage", attacker, victim, attackTraits.Damage)); } } The error is: 'Damage': cannot reference a type through an expression; try 'HWAlphaRelease.GameObject.CombatantGameModel.Damage' instead What am I doing wrong?

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  • Connection Pool error LINQ to SQL

    - by Ved
    Guys, In Our project I have used LINQ to SQL for every kind of database interaction. Now from what I know , When I create and use DataContext object : it opens the connection , crates a transaction , perform the query and closes the connection. Every now and then we are getting Connection pool error on our services and Server. " The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached. " Any idea ? Am I completely off here ? Is this related to SQL Server itself ? We are using LINQ , .Net 3.5 and Sql Server 2008 NOTE: NO DATAREADER IS BEING USED ANYWHERE IN SYSTEM. Thanks

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  • Random sort list with LINQ and Entity Framework in vb.net

    - by Sander Versluys
    I've seen many examples in LINQ but i'm not able to reproduce the same result in vb.net. I have following code: Dim context As New MyModel.Entities() Dim rnd As New System.Random() Dim gardens As List(Of Tuin) = (From t In context.Gardens Where _ t.Approved = True And _ Not t.Famous = True _ Order By rnd.Next() _ Select t).ToList() But i receive an error when binding this list to a control. LINQ to Entities does not recognize the method 'Int32 Next()' method, and this method cannot be translated into a store expression. Any suggestion on how to get this to work?

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  • Linq: convert string to int array

    - by Oops
    I have a function (tointarray) to convert a string into an array of ints, but I am not very satisfied with it. it does the job but there must be a more elegant way to do this, perhaps Linq could help here. unfortunately I am not very good in Linq. do you guys know a better way? my function: { string s1 = "1;2;3;4;5;6;7;8;9;10;11;12"; int[] ia = tointarray(s1, ';'); } int[] tointarray(string value, char sep) { string[] sa = value.Split(sep); int[] ia = new int[sa.Length]; for (int i = 0; i < ia.Length; ++i) { int j; string s = sa[i]; if (int.TryParse(s, out j)) { ia[i] = j; } } return ia; }

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  • Timeout Expired error Using LINQ

    - by Refracted Paladin
    I am going to sum up my problem first and then offer massive details and what I have already tried. Summary: I have an internal winform app that uses Linq 2 Sql to connect to a local SQL Express database. Each user has there own DB and the DB stay in sync through Merge Replication with a Central DB. All DB's are SQL 2005(sp2or3). We have been using this app for over 5 months now but recently our users are getting a Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. Detailed: The strange part is they get that in two differnt locations(2 differnt LINQ Methods) and only the first time they fire in a given time period(~5mins). One LINQ method is pulling all records that match a FK ID and then Manipulating them to form a Heirarchy View for a TreeView. The second is pulling all records that match a FK ID and dumping them into a DataGridView. The only things I can find in common with the 2 are that the first IS an IEnumerable and the second converts itself from IQueryable - IEnumerable - DataTable... I looked at the query's in Profiler and they 'seemed' normal. They are not very complicated querys. They are only pulling back 10 - 90 records, from one table. Any thoughts, suggestions, hints whatever would be greatly appreciated. I am at my wit's end on this.... public IList<CaseNoteTreeItem> GetTreeViewDataAsList(int personID) { var myContext = MatrixDataContext.Create(); var caseNotesTree = from cn in myContext.tblCaseNotes where cn.PersonID == personID orderby cn.ContactDate descending, cn.InsertDate descending select new CaseNoteTreeItem { CaseNoteID = cn.CaseNoteID, NoteContactDate = Convert.ToDateTime(cn.ContactDate). ToShortDateString(), ParentNoteID = cn.ParentNote, InsertUser = cn.InsertUser, ContactDetailsPreview = cn.ContactDetails.Substring(0, 75) }; return caseNotesTree.ToList<CaseNoteTreeItem>(); } AND THIS ONE public static DataTable GetAllCNotes(int personID) { using (var context = MatrixDataContext.Create()) { var caseNotes = from cn in context.tblCaseNotes where cn.PersonID == personID orderby cn.ContactDate select new { cn.ContactDate, cn.ContactDetails, cn.TimeSpentUnits, cn.IsCaseLog, cn.IsPreEnrollment, cn.PresentAtContact, cn.InsertDate, cn.InsertUser, cn.CaseNoteID, cn.ParentNote }; return caseNotes.ToList().CopyLinqToDataTable(); } }

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  • Bidirectional Serialization with Linq

    - by Andy
    Anyone know why only undirectional serialization is supported in the Linq designer? Consider the following example: Say we have a Customer who requested an Order containing Products. We set the Serialization Mode in the Linq designer to Unidirectional to enable serialization. When looking at the code for the Order object, the DataMember attribute is added to all its internal properties such as ID,OrderNumber, etc. and also to the EntitySet of Products, but not to Customer. One can get around this by manually adding the DataMember attribute to Customer, but this becomes quite cumbersome when there's loads of entities in the database.

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  • Linq to SQL, Repository, IList and Persist All

    - by Dr. Zim
    This discusses a repository which returns IList that also uses Linq to SQL as a DAL. Once you do a .ToList(), IQueryable object is gone once you exit the Repository. This means that I need to send the objects back in to the Repo methods .Create(Model model), .Update(Model model), and .Delete(int ID). Assuming that is correct, how do you do the PersistAll()? For example, if you did the following, how would you code that in the repository? Changed a single string property in the object Called .Update(object); Changed a different string property in the object Called .Update(object); Called .PersistAll(), which would update the database with both changed strings. How would you associate the objects in the Repository parameters with the objects in the Linq to Sql data context, especially over multiple calls? I am sure this is a standard thing. Links to examples on the web would be great!

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  • Databind gridview with LINQ

    - by Anders Svensson
    I have two database tables, one for Users of a web site, containing the fields "UserID", "Name" and the foreign key "PageID". And the other with the fields "PageID" (here the primary key), and "Url". I want to be able to show the data in a gridview with data from both tables, and I'd like to do it with databinding in the aspx page. I'm not sure how to do this, though, and I can't find any good examples of this particular situation. Here's what I have so far: <%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="LinqBinding._Default" %> <asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent"> </asp:Content> <asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent"> <h2> Testing LINQ </h2> <asp:GridView ID="GridView1" runat="server" DataSourceID="LinqDataSourceUsers" AutoGenerateColumns="false"> <Columns> <asp:CommandField ShowSelectButton="True" /> <asp:BoundField DataField="UserID" HeaderText="UserID" /> <asp:BoundField DataField="Name" HeaderText="Name" /> <asp:BoundField DataField="PageID" HeaderText="PageID" /> <asp:TemplateField HeaderText="Pages"> <ItemTemplate <asp:DropDownList ID="DropDownList1" DataSourceID="LinqDataSourcePages" SelectedValue='<%#Bind("PageID") %>' DataTextField="Url" DataValueField="PageID" runat="server"> </asp:DropDownList> </ItemTemplate> </asp:TemplateField> </Columns> </asp:GridView> <asp:LinqDataSource ID="LinqDataSourcePages" runat="server" ContextTypeName="LinqBinding.UserDataContext" EntityTypeName="" TableName="Pages"> </asp:LinqDataSource> <asp:LinqDataSource ID="LinqDataSourceUsers" runat="server" ContextTypeName="LinqBinding.UserDataContext" EntityTypeName="" TableName="Users"> </asp:LinqDataSource> </asp:Content> But this only works in so far as it gets the user table into the gridview (that's not a problem), and I get the page data into the dropdown, but here's the problem: I of course get ALL the page data in there, not just the pages for each user on each row. So how do I put some sort of "where" constraint on dropdown for each row to only show the pages for the user in that row? (Also, to be honest I'm not sure I'm getting the foreign key relationship right, because I'm not too used to working with relationships). EDIT: I think I have set up the relationship incorrectly. I keep getting the message that "Pages" doesn't exist as a property on the User object. And I guess it can't since the relationship right now is one way. So I tried to create a many-to-many relationship. Again, my database knowledge is a bit limited, but I added a so called "junction table" with the fields UserID and PageID, same as the other tables' primary keys. I wasn't able to make both of these primary keys in the junction table though (which it looked like some people had in examples I've seen...but since it wasn't possible I guessed they shouldn't be). Anyway, I created a relationship from each table and created new LINQ classes from that. But then what do I do? I set the junction table as the Linq data source, since I guessed I had to do this to access both tables, but that doesn't work. Then it complains there is no Name property on that object. So how do I access the related tables? Here's what I have now with the many-to-many relationship: <%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="ManyToMany._Default" %> <asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent"> </asp:Content> <asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent"> <h2> Many to many LINQ </h2> <asp:GridView ID="GridView1" runat="server" DataSourceID="LinqDataSource1" AutoGenerateColumns="false"> <Columns> <asp:CommandField ShowSelectButton="True" /> <asp:BoundField DataField="UserID" HeaderText="UserID" /> <asp:BoundField DataField="Name" HeaderText="Name" /> <asp:BoundField DataField="PageID" HeaderText="PageID" /> <asp:TemplateField HeaderText="Pages"> <ItemTemplate> <asp:DropDownList ID="DropDownList1" DataSource='<%#Eval("Pages") %>' SelectedValue='<%#Bind("PageID") %>' DataTextField="Url" DataValueField="PageID" runat="server"> </asp:DropDownList> </ItemTemplate> </asp:TemplateField> </Columns> </asp:GridView> <asp:LinqDataSource ID="LinqDataSource1" runat="server" ContextTypeName="ManyToMany.UserPageDataContext" EntityTypeName="" TableName="UserPages"> </asp:LinqDataSource> </asp:Content>

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  • SqlDateTime overflow on INSERT when date is correct using a Linq to SQL DataContext

    - by Jan Hoefnagels
    Dear Linq experts, I get an SqlDateTime overflow error (Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM.) when doing an INSERT using an Linq DataContext connected to SQL Server database when I do the SubmitChanges(). When I use the debugger the date value is correct. Even if I temporary update the code to set the date value to DateTime.Now it will not do the insert. Did anybody found a work-around for this behaviour? Maybe there is a way to check what SQL the datacontext submits to the database.

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  • Confusing Java syntax...

    - by posfan12
    I'm trying to convert the following code (from Wikipedia) from Java to JavaScript: /* * 3 June 2003, [[:en:User:Cyp]]: * Maze, generated by my algorithm * 24 October 2006, [[:en:User:quin]]: * Source edited for clarity * 25 January 2009, [[:en:User:DebateG]]: * Source edited again for clarity and reusability * 1 June 2009, [[:en:User:Nandhp]]: * Source edited to produce SVG file when run from the command-line * * This program was originally written by [[:en:User:Cyp]], who * attached it to the image description page for an image generated by * it on en.wikipedia. The image was licensed under CC-BY-SA-3.0/GFDL. */ import java.awt.*; import java.applet.*; import java.util.Random; /* Define the bit masks */ class Constants { public static final int WALL_ABOVE = 1; public static final int WALL_BELOW = 2; public static final int WALL_LEFT = 4; public static final int WALL_RIGHT = 8; public static final int QUEUED = 16; public static final int IN_MAZE = 32; } public class Maze extends java.applet.Applet { /* The width and height (in cells) of the maze */ private int width; private int height; private int maze[][]; private static final Random rnd = new Random(); /* The width in pixels of each cell */ private int cell_width; /* Construct a Maze with the default width, height, and cell_width */ public Maze() { this(20,20,10); } /* Construct a Maze with specified width, height, and cell_width */ public Maze(int width, int height, int cell_width) { this.width = width; this.height = height; this.cell_width = cell_width; } /* Initialization method that will be called when the program is * run from the command-line. Maze will be written as SVG file. */ public static void main(String[] args) { Maze m = new Maze(); m.createMaze(); m.printSVG(); } /* Initialization method that will be called when the program is * run as an applet. Maze will be displayed on-screen. */ public void init() { createMaze(); } /* The maze generation algorithm. */ private void createMaze(){ int x, y, n, d; int dx[] = { 0, 0, -1, 1 }; int dy[] = { -1, 1, 0, 0 }; int todo[] = new int[height * width], todonum = 0; /* We want to create a maze on a grid. */ maze = new int[width][height]; /* We start with a grid full of walls. */ for (x = 0; x < width; ++x) { for (y = 0; y < height; ++y) { if (x == 0 || x == width - 1 || y == 0 || y == height - 1) { maze[x][y] = Constants.IN_MAZE; } else { maze[x][y] = 63; } } } /* Select any square of the grid, to start with. */ x = 1 + rnd.nextInt (width - 2); y = 1 + rnd.nextInt (height - 2); /* Mark this square as connected to the maze. */ maze[x][y] &= ~48; /* Remember the surrounding squares, as we will */ for (d = 0; d < 4; ++d) { if ((maze[][d][][d] & Constants.QUEUED) != 0) { /* want to connect them to the maze. */ todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]); maze[][d][][d] &= ~Constants.QUEUED; } } /* We won't be finished until all is connected. */ while (todonum > 0) { /* We select one of the squares next to the maze. */ n = rnd.nextInt (todonum); x = todo[n] >> 16; /* the top 2 bytes of the data */ y = todo[n] & 65535; /* the bottom 2 bytes of the data */ /* We will connect it, so remove it from the queue. */ todo[n] = todo[--todonum]; /* Select a direction, which leads to the maze. */ do { d = rnd.nextInt (4); } while ((maze[][d][][d] & Constants.IN_MAZE) != 0); /* Connect this square to the maze. */ maze[x][y] &= ~((1 << d) | Constants.IN_MAZE); maze[][d][][d] &= ~(1 << (d ^ 1)); /* Remember the surrounding squares, which aren't */ for (d = 0; d < 4; ++d) { if ((maze[][d][][d] & Constants.QUEUED) != 0) { /* connected to the maze, and aren't yet queued to be. */ todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]); maze[][d][][d] &= ~Constants.QUEUED; } } /* Repeat until finished. */ } /* Add an entrance and exit. */ maze[1][1] &= ~Constants.WALL_ABOVE; maze[width - 2][height - 2] &= ~Constants.WALL_BELOW; } /* Called by the applet infrastructure to display the maze on-screen. */ public void paint(Graphics g) { drawMaze(g); } /* Called to write the maze to an SVG file. */ public void printSVG() { System.out.format("<svg width=\"%d\" height=\"%d\" version=\"1.1\"" + " xmlns=\"http://www.w3.org/2000/svg\">\n", width*cell_width, height*cell_width); System.out.println(" <g stroke=\"black\" stroke-width=\"1\"" + " stroke-linecap=\"round\">"); drawMaze(null); System.out.println(" </g>\n</svg>"); } /* Main maze-drawing loop. */ public void drawMaze(Graphics g) { int x, y; for (x = 1; x < width - 1; ++x) { for (y = 1; y < height - 1; ++y) { if ((maze[x][y] & Constants.WALL_ABOVE) != 0) drawLine( x * cell_width, y * cell_width, (x + 1) * cell_width, y * cell_width, g); if ((maze[x][y] & Constants.WALL_BELOW) != 0) drawLine( x * cell_width, (y + 1) * cell_width, (x + 1) * cell_width, (y + 1) * cell_width, g); if ((maze[x][y] & Constants.WALL_LEFT) != 0) drawLine( x * cell_width, y * cell_width, x * cell_width, (y + 1) * cell_width, g); if ((maze[x][y] & Constants.WALL_RIGHT) != 0) drawLine((x + 1) * cell_width, y * cell_width, (x + 1) * cell_width, (y + 1) * cell_width, g); } } } /* Draw a line, either in the SVG file or on the screen. */ public void drawLine(int x1, int y1, int x2, int y2, Graphics g) { if ( g != null ) g.drawLine(x1, y1, x2, y2); else System.out.format(" <line x1=\"%d\" y1=\"%d\"" + " x2=\"%d\" y2=\"%d\" />\n", x1, y1, x2, y2); } } Anyway, I was chugging along fairly quickly when I came to a bit that I just don't understand: /* Remember the surrounding squares, as we will */ for (var d = 0; d < 4; ++d) { if ((maze[][d][][d] & Constants.QUEUED) != 0) { /* want to connect them to the maze. */ todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]); maze[][d][][d] &= ~Constants.QUEUED; } } What I don't get is why there are four sets of brackets following the "maze" parameter instead of just two, since "maze" is a two dimensional array, not a four dimensional array. I'm sure there's a good reason for this. Problem is, I just don't get it. Thanks!

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