I have the following code:
Dim getProspect = (From p In dbContext.IRF_Prospects _
Where p.url = prospect_url _
Select p).FirstOrDefault
' If they have a record...
If Not IsDBNull(getProspect) Then
If IsDBNull(getProspect.user_id) Then
' Prepopulate the form with their information.
txtFirst.Text = getProspect.first_name
Else
' Redirect them to login.
Response.Redirect("login.aspx")
End If
When I execute it, it throws an object reference not set to an instance of an object error on getProspect.user_id. Why is it doing this? Shouldn't the fact that I'm verifying it exists using IsDBNull first keep this from happening?
DBNull is not the same as Nothing, and what you have is Nothing. FirstOrDefault, as the name suggests, returns the first item or the default value, which is Nothing for reference types - never DBNull.
Dim getProspect = (From p In dbContext.IRF_Prospects _
Where p.url = prospect_url _
Select p).FirstOrDefault
' If they have a record...
If getProspect IsNot Nothing Then
If IsDBNull(getProspect.user_id) Then
' Prepopulate the form with their information.
txtFirst.Text = getProspect.first_name
Else
' Redirect them to login.
Response.Redirect("login.aspx")
End If
Related
So I am having a problem loading a drop down list in an asp.net web forms site. I am pulling the records from a SQL Server database. I am binding the results to a drop down list.
My problems stems from the fact that I am retrieving 21500 plus rows and it is causing a long delay to the point where the browser throws a message asking if I want to stop a long executing script. If I wait long enough, ~2 minutes it will come back but still runs very slow taking a long time scroll down through the list.
Here is the VB code for the SQL call:
Private Function GetCorInfo(field As String, tblname As String, Optional whereClause As String = "") As DataTable
Dim sqlCmdTxt As String = "Select " & field & " From " & tblname
Using conn As New SqlConnection(corConnection)
Try
conn.Open()
Catch ex As Exception
Master.message = "Unable to open SQL DB connection\nError: SQL101\nPlease contact the Help Desk for support.\n" & HttpUtility.JavaScriptStringEncode(ex.Message)
jsa.alertmessage(passedPage, Master.message)
End Try
Using sqlCmd As New SqlCommand
'Check for where clause
If whereClause <> "" Then
sqlCmdTxt = sqlCmdTxt & whereClause
If whereClause.Substring(7, 6) = "cornum" Then
sqlCmd.Parameters.AddWithValue("#cornum", ddl2.SelectedItem.Text)
End If
End If
If field = "cornum" Then
sqlCmdTxt = sqlCmdTxt & " Order By " & field & " Desc"
End If
sqlCmd.CommandText = sqlCmdTxt
sqlCmd.Connection = conn
Using sqlDT As New DataTable()
Using sqlDA As New SqlDataAdapter(sqlCmd)
Try
sqlDA.Fill(sqlDT)
Return sqlDT
Catch ex As Exception
conn.Close()
Master.message = "Unable to load list.\nError: SQL104\n" & HttpUtility.JavaScriptStringEncode(ex.Message)
jsa.alertmessage(passedPage, Master.message)
Return Nothing
End Try
End Using
End Using
End Using
End Using
End Function
Then when the data table is returned I am binding it to the drop down list using this code:
If Not IsNothing(dt) Then
'Set ddl
With ddl
'Turn on ddl
.Visible = True
'Set Data Source
.DataSource = dt
'Set Text Field
.DataTextField = field1
'Set Value Field
.DataValueField = field1
'Set variable to field value
'Bind Data
.DataBind()
'Assign Variable
field = ddl.SelectedItem.Text
'Check for ddl match
If whereClause <> "" AndAlso ddl1.SelectedIndex = 3 AndAlso ddl.ID = "ddl3" Then
.Items.FindByValue(field).Selected = True
ElseIf whereClause <> "" AndAlso ddl1.SelectedIndex = 3 AndAlso ddl.ID = "ddl4" Then
.Items.Insert(0, New ListItem("Select", "0"))
Else
'Insert first choice
.Items.Insert(0, New ListItem("Select", "0"))
End If
'Set to index 0
.SelectedIndex = 0
End With
Return 1
Else
Return -1
End If
Both sets of codes are run in functions.
How can I speed this up? I have looked at using Session and View State but the number of returned records would cause a bigger slow down if I do that.
Does anyone have any ideas?
Thanks in advance for the help.
So this what i finally did.
Placed a text box for the user to type in the first few char's of a new customer name. Then taking that I build a SQL query that only returns records that match the chars entered.
Much faster and only have at max 35 records...
I have the follwoing code that performs a query and returns a result. However, I looked around and found some examples to take care of null values but I get an error: "Invalid attempt to read when no data is present." I also got the error: "Conversion from type 'DBNull' to type 'Decimal' is not valid."
Can someone help me out with this code to prevent null values from crashing my program?
Private Sub EFFICIENCY_STACKRANK_YTD(ByVal EMPLOYEE As String)
Dim queryString As String = "SELECT " & _
" (SELECT CAST(SUM(TARGET_SECONDS) AS DECIMAL)/ CAST(SUM(ROUTE_SECONDS) AS DECIMAL) FROM dbo.APE_BUSDRIVER_MAIN WITH(NOLOCK) WHERE APE_AREA_OBJID = " & lblAreaOBJID.Text & " AND EMPLOYEE_NAME = '" & EMPLOYEE & "' AND YEAR_TIME = '" & cbYear.Text & "' AND ACTIVE = 1) AS RESULT1" & _
" FROM dbo.APE_BUSDRIVER_MAIN "
Using connection As New SqlConnection(SQLConnectionStr)
Dim command As New SqlCommand(queryString, connection)
connection.Open()
Dim reader As SqlDataReader = command.ExecuteReader()
If reader.Read Then
RESULT1 = reader("RESULT1")
Else
RESULT1 = 0
End If
End Using
End Sub
You have opened the reader, but have not asked it to actually read anything.
After this line:
Dim reader As SqlDataReader = command.ExecuteReader()
add
If reader.Read() Then
and wrap the result reading into this if statement, i.e.
If reader.Read() Then
Dim index As Integer = reader.GetOrdinal("RESULT1")
If reader.IsDBNull(index) Then
RESULT1 = String.Empty
Else
RESULT1 = reader(index)
End If
End If
Note that this works because your SQL should only return a single record. In the event that you were reading multiple records, you would need to call the Read statement in a loop until there were no more records, i.e.
Do While reader.Read()
Loop
I wanted to provide another, more-advanced, answer as an option. Many classes can be extended in .NET like this.
If you are regularly performing "Is NULL" checks like this in your applications, you can choose to extend the DataReader class once to have additional functions available everywhere in your application. Here is an example that creates an extension called "ReadNullAsString()" onto the data reader class. This makes a function that always returns String.Empty when a DbNull is encountered.
Part 1, place this module code in a new class file in App_Code if application is a website, otherwise place where ever you prefer. There are two overloads, one for the field's ordinal position (aka index), and one for the field's ColumnName.
Public Module DataReaderExtensions
''' <summary>
''' Reads fieldName from Data Reader. If fieldName is DbNull, returns String.Empty.
''' </summary>
''' <returns>Safely returns a string. No need to check for DbNull.</returns>
<System.Runtime.CompilerServices.Extension()> _
Public Function ReadNullAsEmptyString(ByVal reader As IDataReader, ByVal fieldName As String) As String
If IsDBNull(reader(fieldName)) Then
Return String.Empty
Else
Return reader(fieldName)
End If
Return False
End Function
''' <summary>
''' Reads fieldOrdinal from Data Reader. If fieldOrdinal is DbNull, returns String.Empty.
''' </summary>
''' <returns>Safely returns a string. No need to check for DbNull.</returns>
<System.Runtime.CompilerServices.Extension()> _
Public Function ReadString(ByVal reader As IDataReader, ByVal fieldOrdinal As Integer) As String
If IsDBNull(reader(fieldOrdinal)) Then
Return ""
Else
Return reader(fieldOrdinal)
End If
Return False
End Function
End Module
Step 2, call the new extension like so:
' no need to check for DbNull now, this functionality is encapsulated in the extension module.
RESULT1 = reader.ReadNullAsEmptyString(index)
'or
RESULT1 = reader.ReadNullAsEmptyString("RESULT1")
I have code that looks like this:
Using dbContext as IRFEntities = New IRFEntities
Dim getProspect = (From p in dbContext.IRF_Prospects _
where p.url = prospect_url _
Select p).FirstOrDefault
If getProspect.user_id Is Nothing Then
' Prepopulate the form with their information.
' These must have a value, so we need to make sure that no column is null in the database.
ddlProgram.SelectedValue = getProspect.program
txtFirst.Text = getProspect.first_name
txtLast.Text = getProspect.last_name
txtAddress.Text = getProspect.address
txtCity.Text = getProspect.city
ddlState.SelectedValue = getProspect.state
txtZip.Text = getProspect.zip
txtPhone.Text = getProspect.phone
txtEmail.Text = getProspect.email_address
txtYearEnrolling.Text = getProspect.enrolling_in
Else
' Redirect them to login.
Response.Redirect("login.aspx")
End If
End Using
I am getting the following error:
System.InvalidOperationException was unhandled by user code
HResult=-2146233079
Message=Nullable object must have a value.
On the following line of code:
txtYearEnrolling.Text = getProspect.enrolling_in
I know why I am getting the error - the value is null in the database. What I'd like to do is pull the value if it exists, but if it doesn't, I'd like it to either take a default value or just leave the field blank. What is the best way to accomplish this?
I have a dropdown list on my page (ddlProgram) which is populated via a database query like so:
Using dbContext as IRFEntities = New IRFEntities
Dim getPrograms = (From p in dbContext.IRF_Program _
Order By p.name _
Select p)
ddlProgram.DataSource = getPrograms
ddlProgram.DataTextField = "name"
ddlProgram.DataValueField = "id"
ddl.Program.DataBind()
End Using
So, for example, one might have a DataTextField of "Education" and an ID of "221".
Now, I prepopulate the form with information about the individual visiting the site (if available) - including the dropdown list like so:
If getProspect IsNot Nothing Then
If getProspect.user_id Is Nothing Then
ddlProgram.SelectedValue = getProspect.Program
End If
End If
The Program property contains a number that matches the ID of a Program. So, for example, this individual might have a Program of "221" which would match the "221" of Education mentioned above.
Currently the application successfully sets the SelectedValue to "221" for the DropDownList (ddlProgram), but the SelectedItem of the DDL remains the same (e.g., if it is initially "History" with an ID of "1" after the prepopulation it is "History" with an ID of "221").
What I'm trying to make happen is that the SelectedItem is updated to item which corresponds with the SelectedValue. So, in the end, if the individual has "221" for "Education" selected when the form is prepopulated they would see Education as the selected item and the selected value would be set correctly, whereas right now the form is showing the wrong SelectedItem but has the right SelectedValue behind the scenes.
Here is a more complete idea of the code flow from the Page_Load event:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Page.IsPostBack = False Then
' If prospect is coming from unique url
Dim prospect_url As String = Page.RouteData.Values("value")
' Save prospect_url into session variable
Session("prospect_url") = prospect_url
Using dbContext As IRFEntities = New IRFEntities
' Prepopulate the programs dropdown.
Dim getPrograms = (From p In dbContext.IRF_Program _
Order By p.name _
Select p)
ddlProgram.DataSource = getPrograms
ddlProgram.DataTextField = "name"
ddlProgram.DataValueField = "id"
ddlProgram.DataBind()
End Using
Using dbContext As IRFEntities = New IRFEntities
' Prepopulate the states dropdown.
Dim getStates = (From p In dbContext.IRF_States _
Order By p.name _
Select p)
ddlState.DataSource = getStates
ddlState.DataTextField = "name"
ddlState.DataValueField = "id"
ddlState.DataBind()
End Using
Using dbContext As IRFEntities = New IRFEntities
' Grab info. about prospect based on unique url.
Dim getProspect = (From p In dbContext.IRF_Prospects _
Where p.url = prospect_url _
Select p).FirstOrDefault
' If they have a record...
If getProspect IsNot Nothing Then
If getProspect.user_id Is Nothing Then
' Prepopulate the form with their information.
' These must have a value, so we need to make sure that no column is null in the database.
ddlProgram.SelectedValue = getProspect.program
txtFirst.Text = getProspect.first_name
txtLast.Text = getProspect.last_name
txtAddress.Text = getProspect.address
txtCity.Text = getProspect.city
ddlState.SelectedValue = getProspect.state
txtZip.Text = getProspect.zip
txtPhone.Text = getProspect.phone
txtEmail.Text = getProspect.email_address
txtYearEnrolling.Text = getProspect.enrolling_in
Else
' Redirect them to login.
Response.Redirect("login.aspx")
End If
End If
End Using
End If
End Sub
What you're doing looks like it should work. If you put a breakpoint after the setting of the value and check the SelectedItem text and value, do they appear as expected or mismatched?
Use the Immediate Window to check:
ddlProgram.SelectedItem.Text
ddlProgram.SelectedItem.Value
If they appear the same then I would presume the binding code is being refired and the list is being regenerated with the first item being selected.
To check this put a break point on the binding code and see if it is fired more than once and correct the order of the methods appropriately.
ADDED:
If it works on your local environment it should work when published, if the code is the same? Looking at your code, I'd start by seperating out some of the databinding code into seperate methods rather than have everything in Page_Load, one becuase it's good practice and two because it will make debugging easier. Further than that I'm not sure what else to suggest.
I had the following code:
If Page.IsPostBack = False Then
' If prospect is coming from unique url
Dim prospect_url As String = Page.RouteData.Values("value")
' Save prospect_url into session variable
Session("prospect_url") = prospect_url
Using dbContext As IRFEntities = New IRFEntities
' Prepopulate the states dropdown.
Dim getStates = (From p In dbContext.IRF_States _
Order By p.name _
Select p)
ddlState.DataSource = getStates
ddlState.DataTextField = "name"
ddlState.DataValueField = "id"
ddlState.DataBind()
' Grab info. about prospect based on unique url.
Dim getProspect = (From p In dbContext.IRF_Prospects _
Where p.url = prospect_url _
Select p).FirstOrDefault
' If they have a record...
If getProspect IsNot Nothing Then
'If IsDBNull(getProspect.user_id) Then
If getProspect.user_id Is Nothing Then
' Prepopulate the form with their information.
' These must have a value, so we need to make sure that no column is null in the database.
txtFirst.Text = getProspect.first_name
txtLast.Text = getProspect.last_name
txtAddress.Text = getProspect.address
txtCity.Text = getProspect.city
ddlState.SelectedValue = getProspect.state
txtZip.Text = getProspect.zip
txtPhone.Text = getProspect.phone
txtEmail.Text = getProspect.email_address
txtYearEnrolling.Text = getProspect.enrolling_in
Else
' Redirect them to login.
Response.Redirect("login.aspx")
End If
End If
End Using
End If
I then added directly below ddlState.DataBind() the following:
' Prepopulate the programs dropdown.
Dim getPrograms = (From p In dbContext.IRF_Program _
Order By p.name _
Select p)
ddlProgram.DataSource = getPrograms
ddlProgram.DataTextField = "name"
ddlProgram.DataValueField = "id"
ddlState.DataBind()
Now I get the error:
The ObjectContext instance has been disposed and can no longer be used for operations that require a connection
If I comment out the inserted code, the code works. Why is this code causing a problem?
You have lost this object:
dbContext
That is the resources (including the connection operations) for this object have already been disposed of and cleaned up. You can re-create the object if you need to databind another drop down list.
Dim dbContext as IRFEntities=Nothing
Using dbContext= New IRFEntities
//perform first databind
End Using
Using dbContext = New IRFEntities
//code to perform second databind
End Using