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  • DataTable.Select Behaves Strangely Using ISNULL Operator on NULL DateTime Column

    - by Paul Williams
    I have a DataTable with a DateTime column, "DateCol", that can be DBNull. The DataTable has one row in it with a NULL value in this column. I am trying to query rows that have either DBNull value in this column or a date that is greater than today's date. Today's date is 5/11/2010. I built a query to select the rows I want, but it did not work as expected. The query was: string query = "ISNULL(DateCol, '" + DateTime.MaxValue + "'") > "' + DateTime.Today "'" This results in the following query: "ISNULL(DateCol, '12/31/9999 11:59:59 PM') > '5/11/2010'" When I run this query, I get no results. It took me a while to figure out why. What follows is my investigation in the Visual Studio immediate window: > dt.Rows.Count 1 > dt.Rows[0]["DateCol"] {} > dt.Rows[0]["DateCol"] == DBNull.Value true > dt.Select("ISNULL(DateCol,'12/31/9999 11:59:59 PM') > '5/11/2010'").Length 0 <-- I expected 1 Trial and error showed a difference in the date checks at the following boundary: > dt.Select("ISNULL(DateCol, '12/31/9999 11:59:59 PM') > '2/1/2000'").Length 0 > dt.Select("ISNULL(DateCol, '12/31/9999 11:59:59 PM') > '1/31/2000'").Length 1 <-- this was the expected answer The query works fine if I wrap the DateTime field in # instead of quotes. > dt.Select("ISNULL(DateCol, #12/31/9999#) > #5/11/2010#").Length 1 My machine's regional settings is currently set to EN-US, and the short date format is M/d/yyyy. Why did the original query return the wrong results? Why would it work fine if the date was compared against 1/31/2000 but not against 2/1/2000?

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  • Why is this code invalid in C#?

    - by mmattax
    The following code will not compile: string foo = "bar"; Object o = foo == null ? DBNull.Value : foo; I get: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DBNull' and 'string' To fix this, I must do something like this: string foo = "bar"; Object o = foo == null ? DBNull.Value : (Object)foo; This cast seems pointless as this is certainly legal: string foo = "bar"; Object o = foo == null ? "gork" : foo; It seems to me that when the ternary branches are of different types, the compiler will not autobox the values to the type object...but when they are of the same type then the autoboxing is automatic. In my mind the first statement should be legal... Can anyone describe why the compiler does not allow this and why the designers of C# chose to do this? I believe this is legal in Java...Though I have not verified this. Thanks. EDIT: I am asking for an understanding of why Java and C# handle this differently, what is going on underneath the scenes in C# that make this invalid. I know how to use ternary, and am not looking for a "better way" to code the examples. I understand the rules of ternary in C#, but I want to know WHY... EDIT (Jon Skeet): Removed "autoboxing" tag as no boxing is involved in this question.

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  • What can be used instead of Datatable in LINQ

    - by Kabi
    I have a SQL query that returns a Datatable: var routesTable = _dbhelper.Select("SELECT [RouteId],[UserId],[SourceName],[CreationTime] FROM [Routes] WHERE UserId=@UserId AND RouteId=@RouteId", inputParams); and then we can work with Datatable object of routesTable if (routesTable.Rows.Count == 1) { result = new Route(routeId) { Name = (string)routesTable.Rows[0]["SourceName"], Time = routesTable.Rows[0]["CreationTime"] is DBNull ? new DateTime() : Convert.ToDateTime(routesTable.Rows[0]["CreationTime"]) }; result.TrackPoints = GetTrackPointsForRoute(routeId); } I want to change this code to linq but I don't know how can I simulate Datatable in LINQ ,I wrote this part: Route result = null; aspnetdbDataContext aspdb = new aspnetdbDataContext(); var Result = from r in aspdb.RouteLinqs where r.UserId == userId && r.RouteId==routeId select r; .... but I don't know how can I change this part: if (routesTable.Rows.Count == 1) { result = new Route(routeId) { Name = (string)routesTable.Rows[0]["SourceName"], Time = routesTable.Rows[0]["CreationTime"] is DBNull ? new DateTime() : Convert.ToDateTime(routesTable.Rows[0]["CreationTime"]) }; would you please tell me how can I do this? EDIT here you can see the whole block of code in original public Route GetById(int routeId, Guid userId) { Route result = null; var inputParams = new Dictionary<string, object> { {"UserId", userId}, {"RouteId", routeId} }; var routesTable = _dbhelper.Select("SELECT [RouteId],[UserId],[SourceName],[CreationTime] FROM [Routes] WHERE UserId=@UserId AND RouteId=@RouteId", inputParams); if (routesTable.Rows.Count == 1) { result = new Route(routeId) { Name = (string)routesTable.Rows[0]["SourceName"], Time = routesTable.Rows[0]["CreationTime"] is DBNull ? new DateTime() : Convert.ToDateTime(routesTable.Rows[0]["CreationTime"]) }; result.TrackPoints = GetTrackPointsForRoute(routeId); } return result; }

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  • Nullable<T> as a parameter

    - by ferch
    I alredy have this: public static object GetDBValue(object ObjectEvaluated) { if (ObjectEvaluated == null) return DBNull.Value; else return ObjectEvaluated; } used like: List<SqlParameter> Params = new List<SqlParameter>(); Params.Add(new SqlParameter("@EntityType", GetDBValue(EntityType))); Now i wanted to keep the same interface but extend that to use it with nullable public static object GetDBValue(int? ObjectEvaluated) { if (ObjectEvaluated.HasValue) return ObjectEvaluated.Value; else return DBNull.Value; } public static object GetDBValue(DateTime? ObjectEvaluated) {...} but i want only 1 function GetDBValue for nullables. How do I do that and keep the call as is is? Is that possible at all? I can make it work like: public static object GetDBValue<T>(Nullable<T> ObjectEvaluated) where T : struct { if (ObjectEvaluated.HasValue) return ObjectEvaluated.Value; else return DBNull.Value; } But the call changes to: Params.Add(new SqlParameter("@EntityID ", GetDBValue<int>(EntityID)));

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  • Generic function to handle DataType Conversion

    - by Tommo1977
    I have the following function in C#, that I want to pass a MySQL DataReader value/object. If the value of the object passed is a DBNull I need to handle it and return a Null value of that data type e.g null int. Otherwise I want to convert the returned value like Convert.ToInt32(value) or similar. public static T ConvertFromDB<T>(object value) { return value == DBNull.Value ? default(T) : (T)value; } Can anyone offer any help on this ?

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  • Preserving NULL values in a Double Variable

    - by Sam
    Hi, I'm working on a vb.net application which imports from an Excel spreadsheet. If rdr.HasRows Then Do While rdr.Read() If rdr.GetValue(0).Equals(System.DBNull.Value) Then Return Nothing Else Return rdr.GetValue(0) End If Loop Else I was using string value to store the double values and when preparing the database statement I'd use this code: If (LastDayAverage = Nothing) Then command.Parameters.AddWithValue("@WF_LAST_DAY_TAG", System.DBNull.Value) Else command.Parameters.AddWithValue("@WF_LAST_DAY_TAG", Convert.ToDecimal(LastDayAverage)) End If I now have some data with quite a few decimal places and the data was put into the string variable in scientific notation, so this seems to be the wrong approach. It didn't seem right using the string variable to begin with. If I use a double or decimal type variable, the blank excel values come across as 0.0. How can I preserve the blank values? Thanks

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  • Good practice to create extension methods that apply to System.Object?

    - by Christian
    Hello, I'm wondering whether I should create extension methods that apply on the object level or whether they should be located at a lower point in the class hierarchy. What I mean is something along the lines of: public static string SafeToString(this Object o) { if (o == null || o is System.DBNull) return ""; else { if (o is string) return (string)o; else return ""; } } public static int SafeToInt(this Object o) { if (o == null || o is System.DBNull) return 0; else { if (o.IsNumeric()) return Convert.ToInt32(o); else return 0; } } //same for double.. etc I wrote those methods since I have to deal a lot with database data (From the OleDbDataReader) that can be null (shouldn't, though) since the underlying database is unfortunately very liberal with columns that may be null. And to make my life a little easier, I came up with those extension methods. What I'd like to know is whether this is good style, acceptable style or bad style. I kinda have my worries about it since it kinda "pollutes" the Object-class. Thank you in advance & Best Regards :) Christian P.S. I didn't tag it as "subjective" intentionally.

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  • Accessing both stored procedure output parameters AND the result set in Entity Framework?

    - by MS.
    Is there any way of accessing both a result set and output parameters from a stored procedure added in as a function import in an Entity Framework model? I am finding that if I set the return type to "None" such that the designer generated code ends up calling base.ExecuteFunction(...) that I can access the output parameters fine after calling the function (but of course not the result set). Conversely if I set the return type in the designer to a collection of complex types then the designer generated code calls base.ExecuteFunction<T>(...) and the result set is returned as ObjectResult<T> but then the value property for the ObjectParameter instances is NULL rather than containing the proper value that I can see being passed back in Profiler. I speculate the second method is perhaps calling a DataReader and not closing it. Is this a known issue? Any work arounds or alternative approaches? Edit My code currently looks like public IEnumerable<FooBar> GetFooBars( int? param1, string param2, DateTime from, DateTime to, out DateTime? createdDate, out DateTime? deletedDate) { var createdDateParam = new ObjectParameter("CreatedDate", typeof(DateTime)); var deletedDateParam = new ObjectParameter("DeletedDate", typeof(DateTime)); var fooBars = MyContext.GetFooBars(param1, param2, from, to, createdDateParam, deletedDateParam); createdDate = (DateTime?)(createdDateParam.Value == DBNull.Value ? null : createdDateParam.Value); deletedDate = (DateTime?)(deletedDateParam.Value == DBNull.Value ? null : deletedDateParam.Value); return fooBars; }

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  • problem with sqldatasource and data binding

    - by Alexander
    I am trying to pull out data from the table I had from the database according to the id which is passed from the URL. However I always get data from id= 1? Why? FYI I took this code directly from the ClubWebsite starter kit and copy and paste it to my project to make several changes, the ClubWebsite one worked fine.. but this one doesn't and can't find any reason why because they both looked exactly the same. <%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Events_View.aspx.cs" Inherits="Events_View" %> <asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server"> </asp:Content> <asp:Content ID="Content2" ContentPlaceHolderID="splash" Runat="Server"> <div id="splash4">&nbsp;</div> </asp:Content> <asp:Content ID="Content3" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"> <div id="content"> <div class="post"> <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ClubDatabase %>" SelectCommand="SELECT dbo.Events.id, dbo.Events.starttime, dbo.events.endtime, dbo.Events.title, dbo.Events.description, dbo.Events.staticURL, dbo.Events.address FROM dbo.Events"> <SelectParameters> <asp:Parameter Type="Int32" DefaultValue="1" Name="id"></asp:Parameter> </SelectParameters> </asp:SqlDataSource> <asp:FormView ID="FormView1" runat="server" DataSourceID="SqlDataSource1" DataKeyNames="id" AllowPaging="false" Width="100%"> <ItemTemplate> <h2> <asp:Label Text='<%# Eval("title") %>' runat="server" ID="titleLabel" /> </h2> <div> <br /> <p> <asp:Label Text='<%# Eval("address") %>' runat="server" ID="addressLabel" /> </p> <p> <asp:Label Text='<%# Eval("starttime","{0:D}") %>' runat="server" ID="itemdateLabel" /> <br /> <asp:Label Text='<%# ShowDuration(Eval("starttime"),Eval("endtime")) %>' runat="server" ID="Label1" /> </p> </div> <p> <asp:Label Text='<%# Eval("description") %>' runat="server" ID="descriptionLabel" /> </p> </ItemTemplate> </asp:FormView> <div class="dashedline"> </div> </div> </div> </asp:Content> using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Data.SqlClient; using System.Configuration; using System.Data; public partial class Events_View : System.Web.UI.Page { const int INVALIDID = -1; protected void Page_Load(object sender, System.EventArgs e) { SqlDataSource1.SelectParameters["id"].DefaultValue = System.Convert.ToString(EventID); } public int EventID { get { int m_EventID; object id = ViewState["EventID"]; if (id != null) { m_EventID = (int)id; } else { id = Request.QueryString["EventID"]; if (id != null) { m_EventID = System.Convert.ToInt32(id); } else { m_EventID = 1; } ViewState["EventID"] = m_EventID; } return m_EventID; } set { ViewState["EventID"] = value; } } protected void FormView1_DataBound(object sender, System.EventArgs e) { DataRowView view = (DataRowView)(FormView1.DataItem); object o = view["staticURL"]; if (o != null && o != DBNull.Value) { string staticurl = (string)o; if (staticurl != "") { Response.Redirect(staticurl); } } } protected string ShowLocationLink(object locationname, object id) { if (id != null && id != DBNull.Value) { return "At <a href='Locations_view.aspx?LocationID=" + Convert.ToString(id) + "'>" + (string)locationname + "</a><br/>"; } else { return ""; } } protected string ShowDuration(object starttime, object endtime) { DateTime starttimeDT = (DateTime)starttime; if (endtime != null && endtime != DBNull.Value) { DateTime endtimeDT = (DateTime)endtime; if (starttimeDT.Date == endtimeDT.Date) { if (starttimeDT == endtimeDT) { return starttimeDT.ToString("h:mm tt"); } else { return starttimeDT.ToString("h:mm tt") + " - " + endtimeDT.ToString("h:mm tt"); } } else { return "thru " + endtimeDT.ToString("M/d/yy"); } } else { return starttimeDT.ToString("h:mm tt"); } } }

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  • DateTime.MinValue vs new DateTime() in C#

    - by MadBoy
    When getting SQL DateTime Resharper suggests to use new DateTime() when value is DBNull.Value. I've always used DateTime.MinValue. Which is the proper way? DateTime varData = sqlQueryResult["Data"] is DateTime ? (DateTime) sqlQueryResult["Data"] : new DateTime();

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  • C#: DataBase Null in RadioButtonList

    - by Vinzcent
    Hey, I would like to have a radiobuttollist were you can select value null. Something like this: <asp:RadioButtonList ID="rblCD" runat="server" SelectedValue='<%# Bind("tblCD") %>'> <asp:ListItem Value="RW">RW</asp:ListItem> <asp:ListItem Value="R">R</asp:ListItem> <asp:ListItem Value="DBNull">None</asp:ListItem> </asp:RadioButtonList> Thanks a lot, Vincent

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  • Unit Testing VS 2008 Using Excel

    - by David
    When using Excel (2003) to provide data for my unit tests it seems to think that when a cell has TRUE / FALSE value that it is null when there has been no preceding cell values e.g. if (TestContext.DataRow["SatisfactionExtremelySatisfied"] != DBNull.Value) model.SatisfactionExtremelySatisfied = (bool)TestContext.DataRow ["SatisfactionExtremelySatisfied"]; Sample Excel Data DataRow SatisfactionExtremelySatisfied 0 1 2 TRUE 3 TRUE When reading the test data using OLEDB the cells with TRUE hold no value but when the preceding cells have the value FALSE entered it correctly gets the values TRUE. Am I missing something?

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  • Is this the best approach using generics to check for nulls

    - by user294747
    public static T IsNull<T>(object value, T defaultValue) { turn ((Object.Equals(value,null)) | (Object.Equals(value,DBNull.Value)) ? defaultValue : (T)value); } public static T IsNull<T>(object value) where T :new() { T defaultvalue = new T(); return IsNull(value, defaultvalue); } Have tested, and can use against data objects, classes and variables. Just want to know if there is better way to go about this.

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  • Asyncronous While Loop?

    - by o7th Web Design
    I have a pretty great SqlDataReader wrapper in which I can map the output into a strongly typed list. What I am finding now is that on larger datasets with larger numbers of columns, performance could probably be a bit better if I can optimize my mapping. In thinking about this there is one section in particular that I am concerned about as it seems to be the heaviest hitter: while (_Rdr.Read()) { T newObject = new T(); for (int i = 0; i <= _Rdr.FieldCount - 1; ++i) { PropertyInfo info = (PropertyInfo)_ht[_Rdr.GetName(i).ToUpper()]; if ((info != null) && info.CanWrite) { info.SetValue(newObject, (_Rdr.GetValue(i) is DBNull) ? default(T) : _Rdr.GetValue(i), null); } } _en.Add(newObject); } _Rdr.Close(); What I would really like to know, is if there is a way that I can make this loop asyncronous? I feel that will make all the difference in the world with this beast :) Here is the entire Map method in case anyone can see where I can make further improvements on it... IList<T> Map<T> // Map our datareader object to a strongly typed list private static IList<T> Map<T>(IDataReader _Rdr) where T : new() { try { Type _t = typeof(T); List<T> _en = new List<T>(); Hashtable _ht = new Hashtable(); PropertyInfo[] _props = _t.GetProperties(); Parallel.ForEach(_props, info => { _ht[info.Name.ToUpper()] = info; }); while (_Rdr.Read()) { T newObject = new T(); for (int i = 0; i <= _Rdr.FieldCount - 1; ++i) { PropertyInfo info = (PropertyInfo)_ht[_Rdr.GetName(i).ToUpper()]; if ((info != null) && info.CanWrite) { info.SetValue(newObject, (_Rdr.GetValue(i) is DBNull) ? default(T) : _Rdr.GetValue(i), null); } } _en.Add(newObject); } _Rdr.Close(); return _en; }catch(Exception ex){ _Msg += "Wrapper.Map Exception: " + ex.Message; ErrorReporting.WriteEm.WriteItem(ex, "o7th.Class.Library.Data.Wrapper.Map", _Msg); return default(IList<T>); } }

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  • Sending changes from multiple tables in disconnected dataset to SQLServer...

    - by Stecy
    We have a third party application that accept calls using an XML RPC mechanism for calling stored procs. We send a ZIP-compressed dataset containing multiple tables with a bunch of update/delete/insert using this mechanism. On the other end, a CLR sproc decompress the data and gets the dataset. Then, the following code gets executed: using (var conn = new SqlConnection("context connection=true")) { if (conn.State == ConnectionState.Closed) conn.Open(); try { foreach (DataTable table in ds.Tables) { string columnList = ""; for (int i = 0; i < table.Columns.Count; i++) { if (i == 0) columnList = table.Columns[0].ColumnName; else columnList += "," + table.Columns[i].ColumnName; } var da = new SqlDataAdapter("SELECT " + columnList + " FROM " + table.TableName, conn); var builder = new SqlCommandBuilder(da); builder.ConflictOption = ConflictOption.OverwriteChanges; da.RowUpdating += onUpdatingRow; da.Update(ds, table.TableName); } } catch (....) { ..... } } Here's the event handler for the RowUpdating event: public static void onUpdatingRow(object sender, SqlRowUpdatingEventArgs e) { if ((e.StatementType == StatementType.Update) && (e.Command == null)) { e.Command = CreateUpdateCommand(e.Row, sender as SqlDataAdapter); e.Status = UpdateStatus.Continue; } } and the CreateUpdateCommand method: private static SqlCommand CreateUpdateCommand(DataRow row, SqlDataAdapter da) { string whereClause = ""; string setClause = ""; SqlConnection conn = da.SelectCommand.Connection; for (int i = 0; i < row.Table.Columns.Count; i++) { char quoted; if ((row.Table.Columns[i].DataType == Type.GetType("System.String")) || (row.Table.Columns[i].DataType == Type.GetType("System.DateTime"))) quoted = '\''; else quoted = ' '; string val = row[i].ToString(); if (row.Table.Columns[i].DataType == Type.GetType("System.Boolean")) val = (bool)row[i] ? "1" : "0"; bool isPrimaryKey = false; for (int j = 0; j < row.Table.PrimaryKey.Length; j++) { if (row.Table.PrimaryKey[j].ColumnName == row.Table.Columns[i].ColumnName) { if (whereClause != "") whereClause += " AND "; if (row[i] == DBNull.Value) whereClause += row.Table.Columns[i].ColumnName + "=NULL"; else whereClause += row.Table.Columns[i].ColumnName + "=" + quoted + val + quoted; isPrimaryKey = true; break; } } /* Only values for column that is not a primary key can be modified */ if (!isPrimaryKey) { if (setClause != "") setClause += ", "; if (row[i] == DBNull.Value) setClause += row.Table.Columns[i].ColumnName + "=NULL"; else setClause += row.Table.Columns[i].ColumnName + "=" + quoted + val + quoted; } } return new SqlCommand("UPDATE " + row.Table.TableName + " SET " + setClause + " WHERE " + whereClause, conn); } However, this is really slow when we have a lot of records. Is there a way to optimize this or an entirely different way to send lots of udpate/delete on several tables? I would really much like to use TSQL for this but can't figure a way to send a dataset to a regular sproc. Additional notes: We cannot directly access the SQLServer database. We tried without compression and it was slower.

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  • DataReader - hardcode ordinals?

    - by David Neale
    When returning data from a DataReader I would typically use the ordinal reference on the DataReader to grab the relevant column: if (dr.HasRows) Console.WriteLine(dr[0].ToString()); (OR dr.GetString(0); OR (string)dr[0];)... I have always done this because I was advised at an early stage that using dr["ColumnName"] or a more elegant way of indexing causes a performance hit. However, whilst everything is becoming increasingly strongly-typed I feel more uncomfortable with this. I'm also aware that the above does not check for DBNull. How should data be returned from a DataReader?

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  • How to split string in group in vb.net

    - by amol kadam
    Hi. i'm amol kadam,I want to know how to split string in two part.My string is in Time format (12:12).& I want to seperate this in hour & minute format.the datatype for all variables are string. for hour variable used strTimeHr & for minute strTimeMin .I tried below code but their was a exception "Index and length must refer to a location within the string. Parameter name: length" If Not (objDS.Tables(0).Rows(0)("TimeOfAccident") Is Nothing Or objDS.Tables(0).Rows(0)("TimeOfAccident") Is System.DBNull.Value) Then strTime = objDS.Tables(0).Rows(0)("TimeOfAccident") 'strTime taking value 12:12 index = strTime.IndexOf(":") 'index taking value 2 lastIndex = strTime.Length 'Lastindex taking value 5 strTimeHr = strTime.Substring(0, index) 'strTime taking value 12 correctly strTimeMin = strTime.Substring(index + 1, lastIndex) 'BUT HERE IS PROBLEM OCCURE strTimeMin Doesn't taking any value Me.NumUpDwHr.Text = strTimeHr Me.NumUpDwMin.Text = strTimeMin End If

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  • SqlDateTime overflow thrown by Typed DataSet Insert

    - by end-user
    I'm using a Typed DataSet with an Insert statement; I have a table that has a smalldatetime field defined to accept null values. When I insert from a .NET 2.0 FormView, I get a "SqlDateTime overflow. Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM." Now, I've read this post, and the parameter as sent to the class constructor is defined as global::System.Nullable<global::System.DateTime> DoB So, it looks like it should accept a Nullable obj. Additionally, the generated code is testing the value sent. if ((DoB.HasValue == true)) { command.Parameters[6].Value = ((System.DateTime)(DoB.Value)); } else { command.Parameters[6].Value = global::System.DBNull.Value; } Specifically, the error is occurring when generated SqlClient.SqlCommand.ExecuteScalar() runs: try { returnValue = command.ExecuteScalar(); } So, I guess my question is: how do I use a Typed DataSet to set a blank value (passed from a FormView on CommandName=Insert) to a null in a database?

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  • problem with null column

    - by Iulian
    One column in my database (of type double) has some null values. I am executing a sored procedure to get the data in my app wipDBTableAdapters.XLSFacturiTableAdapter TAFacturi = new wipDBTableAdapters.XLSFacturiTableAdapter(); var dtfacturi = TAFacturi.GetData(CodProiect); Then i try to do something like this: if (dtfacturi[i].CANTITATE == null) { //do something } this is giving a warning : The result of the expression is always 'false' since a value of type 'double' is never equal to 'null' of type 'double? However when i run my code i get the following exception: StrongTypingException The value for column 'CANTITATE' in table 'XLSFacturi' is DBNull. How am I supposed to resolve this ?

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  • DB4o Linq query - How to check for null strings

    - by Dave
    Hey there - simple query: var q = (from SomeObject o in container where o.SomeInt > 8 && o.SomeString != null //Null Ref here select o; I always get a null reference exception. If I use String.IsNullOrEmpty(o.SomeString) the query takes about 100 times as long, as if I use && o.SomeString != "" (which is way faster, but obviously not correct). I'm guessing because DB4o needs to activate the objects, in order to pass them in to the IsNullOrEmpty call, and can't use the indexes. My question is, what's a better way to check for nulls in this situation? Is there something like: mystring != Db4o.DBNull.Value, or something? Cheers, Dave

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  • OLEDB connection does not read data from excel sheet

    - by Pooja
    Hi All, i am getting a weird problem. i am using OLEDB for excel connection with connection string = Provider=Microsoft.Jet.OLEDB.4.0;Data Source=c:\Execute.xls;Extended Properties=Excel 8.0;"); excel file contains columns with string/integer values. the problem is that sometimes connection read values from sheet absolutly fine but sometimes it missed out some data values and shows them as System.DBNull. the behavior is very inconsistent. please help.

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  • What is wrong with this null check for data reader

    - by Phil
    c.Open() r = x.ExecuteReader If Not r("filename").IsDbnull Then imagepath = "<img src='images/'" & getimage(r("filename")) & " border='0' align='absmiddle'" End If c.Close() r.Close() I have also tried; If r("filename") Is DBNull.Value Then imagepath = String.Empty Else imagepath = "<img src='images/'" & getimage(r("filename")) & " border='0' align='absmiddle'" End If c.Close() r.Close() The error is: Invalid attempt to read when no data is present. The idea of my code is to build an img src string only when data is available. Help greatly appreciated. Thanks

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  • Convert Null Value to String - C#.NET

    - by peace
    foreach (PropertyInfo PropertyItem in this.GetType().GetProperties()) { PropertyItem.SetValue(this, objDataTable.Rows[0][PropertyItem.Name.ToString()], null); } In one of the loops i get this exceptional error: Object of type 'System.DBNull' cannot be converted to type 'System.String'. The error occurs because one of the fields in the database has no value (null), so the string property could not handle it. How can i convert this null to string? I got this solution If you know a shorter or better one, feel free to post it. I'm trying to avoid checking on every loop is current value is null or not.

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  • Excel - referenced values via OleDB from .Net client

    - by ho
    I'm trying to read an Excel file (.xls, I think Excel 2003 compatible) via OleDB, but it fails to get the values for referenced fields. This is my current test code (please note, this is just part of the class): Private m_conn As OleDbConnection Public Sub New(ByVal fileName As String) Dim connString As String = String.Format("Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties=Excel 8.0;", fileName) m_conn = New OleDbConnection(connString) m_conn.Open() End Sub Public Sub GetSheet(ByVal sheet As String) Dim query As String = String.Format("SELECT * FROM [{0}]", sheet) Using cmd As OleDbCommand = m_conn.CreateCommand() cmd.CommandText = query Dim ds As New DataSet() Dim a As New OleDbDataAdapter(cmd) Using rdr As OleDbDataReader = cmd.ExecuteReader() While rdr.Read() Debug.WriteLine(rdr.Item(0).ToString()) End While End Using End Using End Sub But if the value is a reference (something like =+'MySheetName'!K37), I just get a DBNull from the call to rdr.Item(0). I can get around this by automating Excel instead, but would prefer not to have to use Excel automation so wondering if anyone knows how to do it.

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