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  • Most efficient way to check for DBNull and then assign to a variable?

    - by ilitirit
    This question comes up occasionally but I haven't seen a satisfactory answer. A typical pattern is (row is a DataRow): if (row["value"] != DBNull.Value) { someObject.Member = row["value"]; } My first question is which is more efficient (I've flipped the condition): row["value"] == DBNull.Value; // Or row["value"] is DBNull; // Or row["value"].GetType() == typeof(DBNull) // Or... any suggestions? This indicates that .GetType() should be faster, but maybe the compiler knows a few tricks I don't? Second question, is it worth caching the value of row["value"] or does the compiler optimize the indexer away anyway? eg. object valueHolder; if (DBNull.Value == (valueHolder = row["value"])) {} Disclaimers: row["value"] exists. I don't know the column index of the column (hence the column name lookup) I'm asking specifically about checking for DBNull and then assignment (not about premature optimization etc). Edit: I benchmarked a few scenarios (time in seconds, 10000000 trials): row["value"] == DBNull.Value: 00:00:01.5478995 row["value"] is DBNull: 00:00:01.6306578 row["value"].GetType() == typeof(DBNull): 00:00:02.0138757 Object.ReferenceEquals has the same performance as "==" The most interesting result? If you mismatch the name of the column by case (eg. "Value" instead of "value", it takes roughly ten times longer (for a string): row["Value"] == DBNull.Value: 00:00:12.2792374 The moral of the story seems to be that if you can't look up a column by it's index, then ensure that the column name you feed to the indexer matches the DataColumn's name exactly. Caching the value also appears to be nearly twice as fast: No Caching: 00:00:03.0996622 With Caching: 00:00:01.5659920 So the most efficient method seems to be: object temp; string variable; if (DBNull.Value != (temp = row["value"]) { variable = temp.ToString(); } This was a good learning experience.

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  • ASP.Net check value with DBNULL

    - by c11ada
    hey all, i have the following code foreach (DataRowView dr in Data) { if (dr == System.DBNull.Value) { nedID = 1; } } but i get the following error Operator '==' cannot be applied to operands of type 'System.Data.DataRowView' and 'System.DBNull' please can some one advice me on how i can check if the value is null or DBNULL

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  • Dataset field DBNull -> int?

    - by BobClegg
    SQLServer int field. Value sometimes null. DataAdapter fills dataset OK and can display data in DatagridView OK. When trying to retrieve the data programmatically from the dataset the Dataset field retrieval code throws a StronglyTypedException error. [global::System.Diagnostics.DebuggerNonUserCodeAttribute()] public int curr_reading { get { try { return ((int)(this[this.tableHistory.curr_readingColumn])); } catch (global::System.InvalidCastException e) { throw new global::System.Data.StrongTypingException("The value for column \'curr_reading\' in table \'History\' is DBNull.", e); } Got past this by checking for DBNull in the get accessor and returning null but... When the dataset structure is modified (Still developing) my changes (unsurprisingly) are gone. What is the best way to handle this situation? It seems I am stuck with dealing with it at the dataset level. Is there some sort of attribute that can tell the auto code generator to leave the changes in place?

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  • Checking for DBNull throws a StrongTypingException

    - by calico-cat
    I am using a dataset to pull data from a DB. One of the fields in a row is NULL. I know this. However, the following vb.net code throws a StrongTypingException (in the autogenerated get_SomeField() method in the dataset designer): If Not IsDBNull(aRow.SomeField) Then 'do something End If According to documentation and this question it should be fine. edit: If aRow.SomeField is DBNull.Value Then also returns the same error. Argh.

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  • Filtering DBNull With LINQ

    - by Steven
    Why does the following query raise the error below for a row with a NULL value for barrel when I explicitly filter out those rows in the Where clause? Dim query = From row As dbDataSet.conformalRow In dbDataSet.Tables("conformal") _ Where Not IsDBNull(row.Cal) AndAlso tiCal_drop.Text = row.Cal _ AndAlso Not IsDBNull(row.Tran) AndAlso tiTrans_drop.Text = row.Tran _ AndAlso Not IsDBNull(row.barrel) _ Select row.barrel If query.Count() > 0 Then tiBarrel_txt.Text = query(0) Run-time exception thrown : System.Data.StrongTypingException - The value for column 'barrel' in table 'conformal' is DBNull. How should my query / condition be rewritten to work as I intended?

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  • DBnull in Linq query causing problems

    - by nat
    hi there i am doing a query thus: int numberInInterval = (from dsStatistics.J2RespondentRow item in jStats.J2Respondent where item.EndTime > dtIntervalLower && item.EndTime <= dtIntervalUpper select item).count(); there appear to be some dbnulls in the endtime column.. any way i can avoid these? tried adding && where item.endtime != null.. and even != dbnull.value do i have to do a second (first) query to grab all that arent null then run the above one? im sure its super simple fix, but im still missing it.. as per thanks nat

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  • Checking for DBNull

    - by Jim Lahman
    Using a table adapter to a SQL Server database table that returns a NULL record.  We determine the fields are NULL by comparing against System.DBNull Looking the NULL records in SQL Management studio   Using a table adapter to retrieve a record   1: try 2: { 3: this.vTrackingTableAdapter.FillByTrkZone(this.dsL1Write.vTracking, iTrkZone); 4: } 5: catch (Exception ex) 6: { 7: sLogMessage = String 8: .Format("Error getting coil number from tracking table at {0} - {1}", 9: sTrkName, 10: ex.Message); 11: throw new CannotReadTrackingTableException(sLogMessage); 12: }   Looking at the record as it returned from the table adapter:   ItemArrayObject Column [0] ChargeCoilNumber [1] HeadWeldZone [2] TailWeldZone [3] ZoneLen [4] ZoneCoilLen [5] Confirmed [6] Validated [7] EntryWidth [8] EntryThickness   Since each item in the ItemArray is an object, we can test for null   1: if (dsL1Write.vTracking.Rows[0].ItemArray[0] == System.DBNull.Value) 2: { 3: throw new NoCoilAtPORException("NULL coil found at tracking zone " + sTrkName); 4: }   If no records were returned by the table adapter 1: if (dsL1Write.vTracking.Rows.Count == 0) 2: { 3: throw new NoCoilAtPORException("No coils found at tracking zone " + sTrkName); 4: }

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  • How can I include DBNull as a value in my strongly typed dataset?

    - by Beska
    I've created a strongly typed dataset (MyDataSet) in my .NET app. For the sake of simplicity, we'll say it has one DataTable (MyDataTable), with one column (MyCol). MyCol has its DataType property set to "System.Int32", and its AllowDBNull property set to "true". I'd like to manually create a new row, and add it to this dataset. I create the row without a problem, with something like: MyDataSet.MyDataTableRow myRow = MySimpleDataSet.MyDataTable.NewItemRow(); Fine. However, when I try to set the value to DBNull: myRow.MyCol = DBNull.Value; I'm told that I can't do it...that it can't cast that to an int. This makes sense, in a way, since I've defined it to be an int...but then how can I get DBNull in there? Am I not supposed to be able to have DBNull in there? Isn't that what the AllowDBNull property is for? I'm obviously missing something fundemental. Can someone help explain what it is? EDIT: I also tried entering "int?" as the DataType, but Visual Studio throws an error when I enter it, saying that "Column requires a valid DataType."

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  • Name for method that takes a string value and returns DBNull.Value || string

    - by David Murdoch
    I got tired of writing the following code: /* Commenting out irrelevant parts public string MiddleName; public void Save(){ SqlCommand = new SqlCommand(); // blah blah...boring INSERT statement with params etc go here. */ if(MiddleName==null){ myCmd.Parameters.Add("@MiddleName", DBNull.Value); } else{ myCmd.Parameters.Add("@MiddleName", MiddleName); } /* // more boring code to save to DB. }*/ So, I wrote this: public static object DBNullValueorStringIfNotNull(string value) { object o; if (value == null) { o = DBNull.Value; } else { o = value; } return o; } // which would be called like: myCmd.Parameters.Add("@MiddleName", DBNullValueorStringIfNotNull(MiddleName)); If this is a good way to go about doing this then what would you suggest as the method name? DBNullValueorStringIfNotNull is a bit verbose and confusing. I'm also open to ways to alleviate this problem entirely. I'd LOVE to do this: myCmd.Parameters.Add("@MiddleName", MiddleName==null ? DBNull.Value : MiddleName); but that won't work. I've got C# 3.5 and SQL Server 2005 at my disposal if it matters.

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  • Reading Excel by OLEDB reads strings as DBNull

    - by Sathish
    I am reading Excel file using OLEDB in Csharp i have shown the sample excel data what i have F1 F2 F3 F4 India 23 44 4 China 4 8 Month 6 USA 45 Neg 4 When i read this data and check in my DataTable i get Null values for "Month 6" and "Neg" where as i can be able get the F1 column correctly... my connection string is as shown Provider=Microsoft.ACE.OLEDB.12.0;Data Source=[XLSource];Extended Properties=Excel 12.0;

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  • Null safe way to get values from an IDataReader

    - by kumar
    Hi all, (LocalVariable)ABC.string(Name)= (Idatareader)datareader.GetString(0); this name value is coming from database.. what happening here is if this name value is null while reading it's throwing an exception? I am manually doing some if condition here. I don't want to write a manual condition to check all my variables.. I am doing something like this now.. string abc = (Idatareader)datareader.GetValue(0); if(abc = null) //assiging null else assiging abc value is there something like can we write extension method for this? thanks

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  • How to test a lamda expression var query result is null?

    - by mike
    var query = from emp in dbEmp.Employees join dept in dbEmp.Departments on emp.DeptID equals dept.DeptID where dept.DepartmentName.Contains(this.TextBox1.Text) select new { EmpID = emp.EmpID, EmpName = emp.EmpName, Age = emp.Age, Address = emp.Address, DeptName = dept.DepartmentName }; if (query==null) Label1.Text = "no results match your search"; GridView1.DataSource = query; GridView1.DataBind(); Everything works in the right way, but the label doesn't show the message when query result returns null. The label can show without condition(querry==null). So how to test if a var query result returns nothing? Thanks

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  • why DataColumn AllowDbNull is true even if oracle db does not allow null

    - by matti
    Hi. I have column SomeId in table SomeLink. When I look with tOra or Sql Plus Worksheet both state: tOra: Column name Data type Default Null Comment SOMEID INTEGER {null} NOT NULL {null} Sql Plus: SOMEID NOT NULL NUMBER(38) I have authored a method that's intended to give default values to all NOT NULL fields that don't have values: public static void GetDefaultValuesForNonNullColumns(DataRow row) { foreach(DataColumn col in row.Table.Columns) { if (Convert.IsDBNull(row[col]) && !col.AllowDBNull) { if (ColumnIsNumeric(col.DataType)) row[col] = 0; else if (col.DataType == typeof(DateTime)) row[col] = DateTime.Now; else if (col.DataType == typeof(String)) row[col] = string.Empty; else if (col.DataType == typeof(Char)) row[col] = ' '; else throw new Exception(string.Format("Unsupported column type: {0}", col.DataType)); } } } When SOMEID is handled in loop the AllowDBNull = true. I really can't understand. The table is created in DataSet like this: _someLinkAdptr = _dbFactory.CreateDataAdapter(); _someLinkAdptr.SelectCommand = _dbFactory.CreateCommand(); _someLinkAdptr.SelectCommand.Connection = _cnctn; _someLinkAdptr.SelectCommand.CommandText = GetSomeLinkSelectTxtAndParams(_someLinkAdptr.SelectCommand, UndefinedValue.ToString(), UndefinedValue.ToString()); Select command returns no rows. The idea is that I can then use commandbuilder to get InsertCommand without building it myself. The row is added to dataset's table like this: private static void CreateDocLink(int anId, int anotherId) { DataRow row = _someDataSet.Tables["SomeLink"].NewRow(); row["AnId"] = anId; row["AnotherId"] = anotherId; Utility.GetDefaultValuesForNonNullColumns(row); _someDataSet.Tables["SomeLink"].Rows.Add(row); } When DataAdapter is updated to oracle db I get: ORA-01400: cannot insert NULL into (SOMESCHEMA.SOMELINK.SOMEID) Cheers & BR -Matti

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  • How do I pass a DBNull value to a parameterized SELECT statement?

    - by Dan
    I have a SQL statement in C# (.NET Framework 4 running against SQL Server 2k8) that looks like this: SELECT [Column1] FROM [Table1] WHERE [Column2] = @Column2 The above query works fine with the following ADO.NET code: DbParameter parm = Factory.CreateDbParameter(); parm.Value = "SomeValue"; parm.ParameterName = "@Column2"; //etc... This query returns zero rows, though, if I assign DBNull.Value to the DbParameter's Value member even if there are null values in Column2. If I change the query to accommodate the null test specifically: SELECT [Column1] FROM [Table1] WHERE [Column2] IS @Column2 I get an "Incorrect syntax near '@Column2'" exception at runtime. Is there no way that I can use null or DBNull as a parameter in the WHERE clause of a SELECT statement?

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  • How can I assign a DBNull in a better way?

    - by Mike
    Hi, I need to parse value from a datarow and assign it to another datarow.If the input is valid, then I need to parse it to double or else add a dbnull value to the output.I'm doing the following, is there a better way to do it? public double? GetVolume(object data) { string colValue = data == null ? string.Empty : data.ToString(); double volume; if (!Double.TryParse(colValue.ToString(), out volume)) { return null; } return volume; } public void Assign(DataRow theRowInput,DataRow theRowOutput) { double? volume = GetVolume(theRowInput[0]); if(volumne.HasValue) theRowOutput[0] = volume.value; else theRowOutput[0] = DbNull.Value; return theRowOutput; } Thanks, -M

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  • when i merge a data table with a typed dataset, one single field on a single row is DBNull sometimes

    - by benj007
    Hi everybody, I have a strange problem sometimes when I try to merge a data table with a typed dataset my data table is filled in with a stored procedure and when I checked the content of this table it is ok, everything is in there straight after I merge it with my core typed dataset like this : MyTypedDataSet.TheTable.Clear(); MyTypedDataSet.TheTable.Merge(MyDataTable); and now if i check the table in the dataset everything is ok except only one single field on one single row which is DBNull, that makes no sense because the source data table contains the good integer vaue. Thanks a lot in advance guys :)

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  • Advice about insert into SQLCE

    - by Alexander
    i am inserting about 1943 records by these function into SQLCE.This is my insert function.Parameters come from StringReader(string comes from webservice).This function executes 1943 times and takes about 20 seconds.I dropped table's indexes,what can i do to improve it?I create just 1 time mycomm and sqlceresultset. Public Function Insert_Function(ByVal f_Line() As String, ByRef myComm As SqlCeCommand, ByRef rs As SqlCeResultSet) As String Try Dim rec As SqlCeUpdatableRecord = rs.CreateRecord() rec.SetInt32(0, IIf(f_Line(1) = "", DBNull.Value, f_Line(1))) rec.SetInt32(1, IIf(f_Line(2) = "", DBNull.Value, f_Line(2))) rec.SetInt32(2, IIf(f_Line(3) = "", DBNull.Value, f_Line(3))) rec.SetInt32(3, IIf(f_Line(4) = "", DBNull.Value, f_Line(4))) rec.SetValue(4, IIf(f_Line5(5) = "", DBNull.Value, f_Line(5))) rs.Insert(rec) rec = Nothing Catch ex As Exception strerr_col = ex.Message End Try Return strerr_col End Function

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  • How to fix Index out of range exception on idatareader

    - by Phil
    Good morning stack overflow, I have been forced into using the idatareader as opposed to the sqldatareader which has .hasrows available. In my code I am attempting to handle nulls like this: reader = GetContent(pageid) While reader.Read If reader("content") IsNot DBNull.Value Then content = Replace(reader("content"), Chr(38) + Chr(97) + Chr(109) + Chr(112) + Chr(59) + Chr(98) + Chr(104) + Chr(99) + Chr(112) + Chr(61) + Chr(49), "") If reader("id") IsNot DBNull.Value Then contentid = reader("id") End If Else contentid = -1 content = String.Empty End If End While Outputcontent.Text = content I am getting an 'Index Out of Range Exception' here: If reader("content") IsNot DBNull.Value Then The database does 100% contain 'content'

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  • Very interesting problem in Compact Framework

    - by Alexander
    Hi, i have a performance problem while inserting data to sqlce.I'm reading string and making inserts to My tables.In LU_MAM table,i insert 1000 records withing 8 seconds.After Mam tables i make some inserts but my largest table is CR_MUS.When i want to insert record into CR_MUS,it takes too much time.CR_MUS has 2000 records and insert takes 35 seconds.What can be reason?I use same logic in my insert functions.Do u have any idea?I use VS 2008 sp1. Dim reader As StringReader reader = New StringReader(data) cn = New SqlCeConnection(General.ConnString) cn.Open() If myTransfer.ClearTables(cn, cmd) = True Then progress = 0 '------------------------------------------ cmd = New SqlServerCe.SqlCeCommand Dim rs As SqlCeResultSet cmd.Connection = cn cmd.CommandType = CommandType.TableDirect Dim rec As SqlCeUpdatableRecord ' name of table While reader.Peek > -1 If strerr_col = "" Then satir = reader.ReadLine() ayrac = Split(satir, "|") If ayrac(0).ToString() = "LC" Then prgsbar.Maximum = Convert.ToInt32(ayrac(1)) ElseIf ayrac(0).ToString = "PPAR" Then . If ayrac(2).ToString <> General.PMVer Then ShowWaitCursor(False) txtDurum.Text = "Wrong Version" Exit Sub End If If p_POCKET_PARAMETERS = True Then cmd.CommandText = "POCKET_PARAMETERS" txtDurum.Text = "POCKET_PARAMETERS" rs = cmd.ExecuteResultSet(ResultSetOptions.Updatable) rec = rs.CreateRecord() p_POCKET_PARAMETERS = False End If strerr_col = myVERI_AL.POCKET_PARAMETERS_I(ayrac, cmd, rs, rec) prgsbar.Value += 1 ElseIf ayrac(0).ToString() = "MAM" Then If p_LU_MAM = True Then txtDurum.Text = "LU_MAM " cmd.CommandText = "LU_MAM" rs = cmd.ExecuteResultSet(ResultSetOptions.Updatable) rec = rs.CreateRecord() p_LU_MAM = False End If strerr_col = myVERI_AL.LU_MAM_I(ayrac, cmd, rs, rec) prgsbar.Value += 1 ElseIf ayrac(0).ToString = "KMUS" Then If p_CR_MUS = True Then cmd.CommandText = "CR_MUS" txtDurum.Text = "CR_MUS" rs = cmd.ExecuteResultSet(ResultSetOptions.Updatable) rec = rs.CreateRecord() p_TR_KAMPANYA_MALZEME = False End If strerr_col = myVERI_AL.CR_MUS_I(ayrac, cmd, rs, rec) prgsbar.Value += 1 end while Public Function CR_KAMPANYA_MUSTERI_I(ByVal f_Line() As String, ByRef myComm As SqlCeCommand, ByRef rs As SqlCeResultSet, ByRef rec As SqlCeUpdatableRecord) As String Try rec.SetValue(0, If(f_Line(1) = String.Empty, DirectCast(DBNull.Value, Object), f_Line(1))) rec.SetValue(1, If(f_Line(2) = String.Empty, DirectCast(DBNull.Value, Object), f_Line(2))) rec.SetValue(2, If(f_Line(3) = String.Empty, DirectCast(DBNull.Value, Object), f_Line(3))) rec.SetValue(3, If(f_Line(5) = String.Empty, DirectCast(DBNull.Value, Object), f_Line(5))) rec.SetValue(4, If(f_Line(6) = String.Empty, DirectCast(DBNull.Value, Object), f_Line(6))) rs.Insert(rec) Catch ex As Exception strerr_col = ex.Message End Try Return strerr_col End Function

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  • Can't set Visible attribute in ASP.NET Panels

    - by RichW
    I am having trouble with visible attribute of an ASP.NET Panel control. I have a page that calls a database table and returns the results in a datagrid. Requirements If some of the returned values are null I need to hide the image that's next to it. I am using a Panel to determine whether to hide or show the image but am having trouble with the statement: visible='<%# Eval("addr1") <> DBNull.Value %>' I have tried these as well: visible='<%# Eval("addr1") <> DBNull.Value %>' visible='<%# IIf(Eval("addr1") Is DbNull.Value, "False","True") %>' Code is below: <asp:TemplateField > <ItemTemplate> <%# Eval("Name")%> <p> <asp:Panel runat="server" ID="Panel1" visible='<%# Eval("addr1") <> DBNull.Value %>'> <asp:Image Id="imgHouse" runat="server" AlternateText="Address" SkinId="imgHouse"/> </asp:Panel> <%# Eval("addr1") %><p> </ItemTemplate> </asp:TemplateField> What am I doing wrong? Edit If I use visible='<%# IIf(Eval("addr1") Is DbNull.Value, "False","True") %>' I get the following error: Compiler Error Message: CS1026: ) expected

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  • Creating a Dynamic DataRow for easier DataRow Syntax

    - by Rick Strahl
    I've been thrown back into an older project that uses DataSets and DataRows as their entity storage model. I have several applications internally that I still maintain that run just fine (and I sometimes wonder if this wasn't easier than all this ORM crap we deal with with 'newer' improved technology today - but I disgress) but use this older code. For the most part DataSets/DataTables/DataRows are abstracted away in a pseudo entity model, but in some situations like queries DataTables and DataRows are still surfaced to the business layer. Here's an example. Here's a business object method that runs dynamic query and the code ends up looping over the result set using the ugly DataRow Array syntax:public int UpdateAllSafeTitles() { int result = this.Execute("select pk, title, safetitle from " + Tablename + " where EntryType=1", "TPks"); if (result < 0) return result; result = 0; foreach (DataRow row in this.DataSet.Tables["TPks"].Rows) { string title = row["title"] as string; string safeTitle = row["safeTitle"] as string; int pk = (int)row["pk"]; string newSafeTitle = this.GetSafeTitle(title); if (newSafeTitle != safeTitle) { this.ExecuteNonQuery("update " + this.Tablename + " set safeTitle=@safeTitle where pk=@pk", this.CreateParameter("@safeTitle",newSafeTitle), this.CreateParameter("@pk",pk) ); result++; } } return result; } The problem with looping over DataRow objecs is two fold: The array syntax is tedious to type and not real clear to look at, and explicit casting is required in order to do anything useful with the values. I've highlighted the place where this matters. Using the DynamicDataRow class I'll show in a minute this code can be changed to look like this:public int UpdateAllSafeTitles() { int result = this.Execute("select pk, title, safetitle from " + Tablename + " where EntryType=1", "TPks"); if (result < 0) return result; result = 0; foreach (DataRow row in this.DataSet.Tables["TPks"].Rows) { dynamic entry = new DynamicDataRow(row); string newSafeTitle = this.GetSafeTitle(entry.title); if (newSafeTitle != entry.safeTitle) { this.ExecuteNonQuery("update " + this.Tablename + " set safeTitle=@safeTitle where pk=@pk", this.CreateParameter("@safeTitle",newSafeTitle), this.CreateParameter("@pk",entry.pk) ); result++; } } return result; } The code looks much a bit more natural and describes what's happening a little nicer as well. Well, using the new dynamic features in .NET it's actually quite easy to implement the DynamicDataRow class. Creating your own custom Dynamic Objects .NET 4.0 introduced the Dynamic Language Runtime (DLR) and opened up a whole bunch of new capabilities for .NET applications. The dynamic type is an easy way to avoid Reflection and directly access members of 'dynamic' or 'late bound' objects at runtime. There's a lot of very subtle but extremely useful stuff that dynamic does (especially for COM Interop scenearios) but in its simplest form it often allows you to do away with manual Reflection at runtime. In addition you can create DynamicObject implementations that can perform  custom interception of member accesses and so allow you to provide more natural access to more complex or awkward data structures like the DataRow that I use as an example here. Bascially you can subclass DynamicObject and then implement a few methods (TryGetMember, TrySetMember, TryInvokeMember) to provide the ability to return dynamic results from just about any data structure using simple property/method access. In the code above, I created a custom DynamicDataRow class which inherits from DynamicObject and implements only TryGetMember and TrySetMember. Here's what simple class looks like:/// <summary> /// This class provides an easy way to turn a DataRow /// into a Dynamic object that supports direct property /// access to the DataRow fields. /// /// The class also automatically fixes up DbNull values /// (null into .NET and DbNUll to DataRow) /// </summary> public class DynamicDataRow : DynamicObject { /// <summary> /// Instance of object passed in /// </summary> DataRow DataRow; /// <summary> /// Pass in a DataRow to work off /// </summary> /// <param name="instance"></param> public DynamicDataRow(DataRow dataRow) { DataRow = dataRow; } /// <summary> /// Returns a value from a DataRow items array. /// If the field doesn't exist null is returned. /// DbNull values are turned into .NET nulls. /// /// </summary> /// <param name="binder"></param> /// <param name="result"></param> /// <returns></returns> public override bool TryGetMember(GetMemberBinder binder, out object result) { result = null; try { result = DataRow[binder.Name]; if (result == DBNull.Value) result = null; return true; } catch { } result = null; return false; } /// <summary> /// Property setter implementation tries to retrieve value from instance /// first then into this object /// </summary> /// <param name="binder"></param> /// <param name="value"></param> /// <returns></returns> public override bool TrySetMember(SetMemberBinder binder, object value) { try { if (value == null) value = DBNull.Value; DataRow[binder.Name] = value; return true; } catch {} return false; } } To demonstrate the basic features here's a short test: [TestMethod] [ExpectedException(typeof(RuntimeBinderException))] public void BasicDataRowTests() { DataTable table = new DataTable("table"); table.Columns.Add( new DataColumn() { ColumnName = "Name", DataType=typeof(string) }); table.Columns.Add( new DataColumn() { ColumnName = "Entered", DataType=typeof(DateTime) }); table.Columns.Add(new DataColumn() { ColumnName = "NullValue", DataType = typeof(string) }); DataRow row = table.NewRow(); DateTime now = DateTime.Now; row["Name"] = "Rick"; row["Entered"] = now; row["NullValue"] = null; // converted in DbNull dynamic drow = new DynamicDataRow(row); string name = drow.Name; DateTime entered = drow.Entered; string nulled = drow.NullValue; Assert.AreEqual(name, "Rick"); Assert.AreEqual(entered,now); Assert.IsNull(nulled); // this should throw a RuntimeBinderException Assert.AreEqual(entered,drow.enteredd); } The DynamicDataRow requires a custom constructor that accepts a single parameter that sets the DataRow. Once that's done you can access property values that match the field names. Note that types are automatically converted - no type casting is needed in the code you write. The class also automatically converts DbNulls to regular nulls and vice versa which is something that makes it much easier to deal with data returned from a database. What's cool here isn't so much the functionality - even if I'd prefer to leave DataRow behind ASAP -  but the fact that we can create a dynamic type that uses a DataRow as it's 'DataSource' to serve member values. It's pretty useful feature if you think about it, especially given how little code it takes to implement. By implementing these two simple methods we get to provide two features I was complaining about at the beginning that are missing from the DataRow: Direct Property Syntax Automatic Type Casting so no explicit casts are required Caveats As cool and easy as this functionality is, it's important to understand that it doesn't come for free. The dynamic features in .NET are - well - dynamic. Which means they are essentially evaluated at runtime (late bound). Rather than static typing where everything is compiled and linked by the compiler/linker, member invokations are looked up at runtime and essentially call into your custom code. There's some overhead in this. Direct invocations - the original code I showed - is going to be faster than the equivalent dynamic code. However, in the above code the difference of running the dynamic code and the original data access code was very minor. The loop running over 1500 result records took on average 13ms with the original code and 14ms with the dynamic code. Not exactly a serious performance bottleneck. One thing to remember is that Microsoft optimized the DLR code significantly so that repeated calls to the same operations are routed very efficiently which actually makes for very fast evaluation. The bottom line for performance with dynamic code is: Make sure you test and profile your code if you think that there might be a performance issue. However, in my experience with dynamic types so far performance is pretty good for repeated operations (ie. in loops). While usually a little slower the perf hit is a lot less typically than equivalent Reflection work. Although the code in the second example looks like standard object syntax, dynamic is not static code. It's evaluated at runtime and so there's no type recognition until runtime. This means no Intellisense at development time, and any invalid references that call into 'properties' (ie. fields in the DataRow) that don't exist still cause runtime errors. So in the case of the data row you still get a runtime error if you mistype a column name:// this should throw a RuntimeBinderException Assert.AreEqual(entered,drow.enteredd); Dynamic - Lots of uses The arrival of Dynamic types in .NET has been met with mixed emotions. Die hard .NET developers decry dynamic types as an abomination to the language. After all what dynamic accomplishes goes against all that a static language is supposed to provide. On the other hand there are clearly scenarios when dynamic can make life much easier (COM Interop being one place). Think of the possibilities. What other data structures would you like to expose to a simple property interface rather than some sort of collection or dictionary? And beyond what I showed here you can also implement 'Method missing' behavior on objects with InvokeMember which essentially allows you to create dynamic methods. It's all very flexible and maybe just as important: It's easy to do. There's a lot of power hidden in this seemingly simple interface. Your move…© Rick Strahl, West Wind Technologies, 2005-2011Posted in CSharp  .NET   Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Page_load event firing twice. User control not properly loading

    - by Phil
    Here is the code I am using to pull my usercontrol (content.ascx): Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load 'load module If TheModule = "content" Then Dim control As UserControl = LoadControl("~\Modules\Content.ascx") Controls.Add(control) End If End Sub Within the usercontrol is the following code (data access taken care of by DAAB and ive replaced sql statements with 'sql'): Imports System.Data.SqlClient Imports System.Data Imports System.Web.Configuration Imports Microsoft.Practices.EnterpriseLibrary.Common Imports Microsoft.Practices.EnterpriseLibrary.Data Partial Class Modules_WebUserControl Inherits System.Web.UI.UserControl Dim db As Database = DatabaseFactory.CreateDatabase() Dim command As SqlCommand 'database Dim reader As IDataReader 'general vars Dim pageid As Integer Dim did As Integer Dim contentid As Integer Dim dotpos As String Dim ext As String Dim content As String Dim folder As String Dim downloadstring As String Function getimage(ByVal strin As String) As String If strin > "" Then dotpos = InStrRev(strin, ".") ext = Right(strin, Len(strin) - dotpos) getimage = ext & ".gif" Else getimage = String.Empty End If Return getimage End Function Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load, Me.Load 'test Response.Write("(1 Test from within page_load)") 'get session vars folder = Session("folder") pageid = Session("pageid") did = Session("did") 'main content command = db.GetSqlStringCommand("sql") db.AddInParameter(command, "@pageid", DbType.Int32, pageid) reader = db.ExecuteReader(command) While reader.Read If reader("content") IsNot DBNull.Value Then content = Replace(reader("content"), Chr(38) + Chr(97) + Chr(109) + Chr(112) + Chr(59) + Chr(98) + Chr(104) + Chr(99) + Chr(112) + Chr(61) + Chr(49), "") If reader("id") IsNot DBNull.Value Then contentid = reader("id") End If Else contentid = -1 content = String.Empty End If End While Outputcontent.Text = content 'contacts info If did = 0 Then command = db.GetSqlStringCommand("sql") db.AddInParameter(command, "@contentid", DbType.Int32, contentid) reader = db.ExecuteReader(command) While reader.Read() Contactinforepeater.DataSource = reader Contactinforepeater.DataBind() End While End If If Not did = 0 Then command = (db.GetSqlStringCommand("sql") db.AddInParameter(command, "@contentid", DbType.Int32, contentid) db.AddInParameter(command, "@did", DbType.Int32, did) reader = db.ExecuteReader(command) While reader.Read Contactinforepeater.DataSource = reader Contactinforepeater.DataBind() End While End If 'downloads box command = db.GetSqlStringCommand("sql") db.AddInParameter(command, "@contentid", DbType.Int32, contentid) reader = db.ExecuteReader(command) While reader.Read If reader("filename") IsNot DBNull.Value Then downloadstring += "<a href='/documents/" & folder & "/" & reader("filename") & "'>" downloadstring += "<img src=images/" & getimage(reader("filename")) & " border=0 align=absmiddle />" End If If reader("filesize") IsNot DBNull.Value Then downloadstring += Convert.ToInt32((reader("filesize") / 1000)) & "kb - " End If If reader("filename") IsNot DBNull.Value Then downloadstring += "<a href='/documents/" & Session("folder") & "/" & reader("filename") & "'>" & reader("description") & "</a><br />" End If End While Dim downloadsarray As ArrayList downloadsarray = New ArrayList If downloadstring IsNot Nothing Then downloadsarray.Add(downloadstring) End If If downloadsarray.Count > 0 Then DownloadsRepeater.DataSource = downloadsarray DownloadsRepeater.DataBind() End If 'get links command = db.GetSqlStringCommand("sql") db.AddInParameter(command, "@contentid", DbType.Int32, contentid) reader = db.ExecuteReader(command) While reader.Read Linksrepeater.DataSource = reader Linksrepeater.DataBind() End While End Sub End Class Now instead of seeing my page content and what should be within the repeaters on the page all I get is 2 x the output of Response.Write("(1 Test from within page_load)") (1 Test from within page_load)(1 Test from within page_load) This leads me to believe the page_load is firing twice, but not properly displaying all the information. Please can one of you willing experts help me to get this working? Thanks a lot in advance

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