I'm trying to test a varbinary(max) field to see if it's null. I'm trying to figure out if it's a null or not in the select statement, hoping to avoid having to do this locally for every row of the returned dataset. This is the SQL I'm using,
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A partner of ours is making a call to a web service that includes a parameter called token. Token is the result of an MD5 hash of two numbers, and helps us authenticate that the user using our partners system. Our partner asks the user for two strings, concatenates them, runs them through MD5, and then calls our web service. The result of the MD5 is the token, and it is submitted to us as a string.
We store valid tokens in a DB - since we use the SQL Server to compute the tokens on our end, SQL seemed to be happiest storing the tokens as a varbinary, which is its native result for an MD5 computation.
We have two pieces of code that attempt to do the same thing - run a select query that pulls out a value based on the token submitted. One uses a dynamic query (which is a problem), but it works. The other one attempts to do the same thing in a parameterized (safer) fashion, it does not work - it is unable to locate the token.
Here's the two competing attempts. First, the parameterized version which fails:
byteArrayToken = System.Text.UnicodeEncoding.Unicode.GetBytes(stringToken)
scSelectThing.CommandText = "select thing from tokenstable where token=@token"
Dim param As SqlParameter = scSelectThing.Parameters.Add("@token",
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I use a VARBINARY(MAX) column, because I have no idea what is going to be put into it. All I know is that as of this point in time, the data will be one of many traditional data types(Integer, String, DateTime, etc.)I also have another column that is meant to indicate the DataType so the .NET application can handle the data and validate input accordingly.Right now, for testing, I have a DataType table in my database that stores the "supported" datatypes for the VARBINARY column, and a foreign key linking to the column meant to indicate the DataType. This works perfectly, but it feels akward.
View 2 RepliesWhen I try to query an entity that has a varbinary field in it I am getting error:"The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities."
Here is my query:
Dim query = From entity In db.Entity
Where entity.Id= Id
Select entity.VarBinaryField
[code]....
The error gets generated when I check that the query isNot nothing.
Some tables I am dealing with have null values and are throwing errors. So far ive tried a few solutions to deal with the nulls with no success.Here are the code samples from my efforts so far;
If (r("datemodified").Equals(DBNull.Value)) Then
datemodified = String.Empty
Else[code]....
i have ran the query and it is working ok (i.e all the cols exist)
Dim myreader As SqlDataReader = cmd.ExecuteReader
'read information from the database and give the values to the arguments(column_1, and column_2)
While myreader.Read
column_1 = myreader.GetString(1)
column_2 = myreader.GetString(2)
.....
I get an error when the data returned from myreader.GetString(2) is NULL. How do I check for nulls before assigning column_2 a value?
Is there any way to convert null terminated string to normal string.I mean I can easily make a program to find the location of vbnull but there has to be a built in function for that.
View 15 RepliesSome tables I am dealing with have null values and are throwing errors. So far ive tried a few solutions to deal with the nulls with no success.
Here are the code samples from my efforts so far;
If (r("datemodified").Equals(DBNull.Value)) Then
datemodified = String.Empty
[code].....
I am looping thorugh a datatable and and printing each row to the console and I keep on getting a dbnull error. I inserted an if statement in my loop to try and catch it, but I can't seem to get it to work.
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I am building a data based application using VB 2008 an SQL Express. I need to create textboxes on my form using code, (With & End With) method. I need a simple code string that will allow the app to check if the field to wich the textbox wil be databound is Nul, If so the textbox will not be created.
View 8 RepliesI using ADO to get som values from a SQL DB one off the fields can have the value NULL And if i use:
txtinfo.Text = RS(
"info").value
Then i get an error.I have try with IS NULL - but that dosn't work
how to delete row in a CSV file where there is a null value in a partcular column? I am using VB. There are three columns I am using Post Date, Account Number, and Credit Amount. I want to delete all rows with null values in the Account Number column. I am very new to VB, took one class. I am using the Microsoft.VisualBasic.FileIO.TextFieldParser?
View 1 RepliesI am using visual studio 2010. I have a text box bound to a sql datetime field.I have to be able to either set or clear the text box. I can set it to any date fine, but when I try to clear it I am unable to save the record.i am using the binding navigator to save.
View 5 RepliesQuestion is: How to test for null value of a field in an ADO recordset.Using Visual Studio 2010 Ultimate - VB.NET
ADO Connection to ODBC database
I am working with a table that contains about 10,000 records of which I need to do additional processing on about 1500. The records I need to process are qualified by the field'Cataloged' = True. The problem I have is the table allows for True, False or Null values (I have no direct control of the table to change from allowing Null) for the field I need to test.I run into errors when the value of the field is Null and need to figure out how to determine its Null state prior to trying to qualify the field as True or False value to prevent the errors.
I have an ASP.NET application that crashes when a null date value is returned.
The code line is:
excelWorksheet.Cells("A" & xlRowCounter).Value = IIf(IsDBNull(dRow("sysdate")), "", Format(dRow("sysdate"), "MM/dd/yyyy"))
Error message:
ERROR: System.ArgumentException: Argument 'Expression' is not a valid value.
How would I check for a null date, and replace it with "" in my app ?
I use following codes to display image from sql server. [code]...
View 3 RepliesI have a field in a datatable (dt) that can be integer or NULL.
View 7 Repliesi have a maskedtextbox which will accept only date in the format of "DD-MM-yyyy" no i want to insert this date in my db. i have done this successfully.
Now i want to insert null value in through that maskedtextbox .
I have a databound ComboBox on my form. Is there any way that I can make the first field blank.
I can do this with a DropDownList in the HTML part of .Net but is there a way to do it for a ComboBox?
I am trying to do a SQL query to see if an Address already exists in my database. My addresses are structure like this:
line1
line2
line3
city
state
zipcode
country
Sometimes line2 and line3 are NULL values in my database.I am using .NET TableAdapter and DataTable to make my query. When I try to pass in my line2 parameter (@line2) it is equal to a string with value = nothing. My database does not interpret this as NULL and says the records don't match, but I know they do? How do I pass in a string = nothing and have it compare to a NULL value in the database as being equal? I have tried string = DBNULL.value but won't compile.I have done similar comparisons with integers etc. using integer = Nullable (of integer) but this does not exist for strings.
I have in my DB a few number fields, but I would like put null values or empty values in some of this fields...
I had try this but without results:
If valorcolocardebito = 0 Then
valorcolocardebito = Nothing
End If
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I am calling a Java-script function, in that i am passing the value of hidden field, that hidden field i want to use at server-side, but the value of hidden field is null.[code]...
View 1 RepliesWhy when I try to save a null value from textbox at sql server 0 is saved?
View 2 RepliesI key-in data from textbox to datagridvie..........the date data the format datatable is:
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I've got a table that caches calculated values for certain dates. I want to use LINQ to select all rows where the calculated value fields are null.But when I use isNothing I get an error that LINQ can't translate this into T-SQL. Is there a way to select null values with link, like this...?
Dim var = From rec As Record In myDataContext.Records Where IsNothing(rec.calculatedValue) Select rec
Other posts on stackoverflow mostly discuss how to avoid or check for null values with LINQ.
Note: I can't just set cacluatedValue's default to -1 to flag records whose calculated value has not been set (and then select those records) because I run queries that sum/average the calculated values. Selecting nulls seems cleaner and less bug-prone.
Im writing an app which connects to a SQL Server database, via datasources / datatable.When Im looking at my .xsd I can see DataTables containing DataColumns. Each DataColumn has a 'NullValue' property which defaults to '(Throw exception)'.Because I have nulls in my tables I have gone through the fields and set all System.String fields to NullValue = 'Empty', System.int32 field to NullValue = 0.
View 1 RepliesI require the expression which determines if a Data Item in a DataRow is null.
Required Code
If MyDataSet.Tables("MyTable")Rows("MyRow").Item("CheckingItem") [IS NULL] Then
'[Do Something]
End If
Attempted Code Resulting in Thrown Exceptions
I have attempted the following code which resulted in the exceptions posted under them.
If CType(ds.Tables("MyTable").Rows(0).Item(2),System.String) = "" Then
Me.lblOutput.Text = "Good"
End If
System.InvalidCastException: Conversion from type 'DBNull' to type 'String' is not valid.
I have the following query that I use to create a new record in a database. If I leave any field on the form blank, for example, it throws the error "Memo.Lastname" cannot be a zero length string. Other than that the query executes appropriately.
Private Sub cmdSaveMemo_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles cmdSaveMemo.Click
If Len(Me.txtMemoID.Text) <> 0 Then
Memo.SaveMemo
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I there a way to set up my DataTable so a field (or all fields can allow nulls if you can't set just 1 field) so oIDbDataAdapter.Fill won't leave out DataRows where a field contains a null value?
Dim oSqlCommand As SqlClient.SqlCommand
Dim oIDbDataAdapter As System.Data.IDbDataAdapter
oSqlCommand = New System.Data.SqlClient.SqlCommand( _
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I have a date time picker bould to a Nullable Datetime field in a sql server datatable. The ShowCheckBox option is set to true. If the user unchecks the checkbox on the datetimepicker I would like to the field to be set back to null in the DataTable. The default behaveour does not seem to do this and there is no specific event for the uncheck.
Private Sub dtpCertDate_ValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles dtpCertDate.ValueChanged
If dtpCertDate.Focused Then
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