C# - Check A Datareader For Null?
Feb 10, 2011
I have an aspx page which allows a user to submit modified entries into the database, but when the user clicks Submit to fire the stored procedure I want to first run a check to see if a modified row with the same relationship exists.I am passing the results of the following query:
SELECT SwitchRoom.ModifiedID FROM SwitchRoom WHERE
SwitchRoomID = @ChkSwitchRmID", constring;
into a DataReader to determine if that relationship exists.I need it to determine whether the reader returns NULL to allow the procedure to execute, if it doesn't, then don't allow the user to save the information.I've tried the following:
if (dbreader = NULL)
{
Fire Procedure
}
else
{
"Error Message"
}
and I've even tried passing the reader into a datatable and running it against that without any luck.
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Feb 16, 2011
I have the following code
public class ProductDetails
{
private string _productid;
public string ProductID
{
get { return _productid; }
}
private string _description;
public string Description
{
get { return _description; }
}
private string _image;
public string Image
{
get { return _image; }
}
public ProductDetails(string productid, string description, string image)
{
_productid = productid;
_description = description;
_image = image;
}
}
public class DataAccess
{
private static string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
public ProductDetails GetProductDetails()
{
SqlConnection con = new SqlConnection(connectionString);
SqlCommand cmd = new SqlCommand("ProductDetails", con);
cmd.CommandType = CommandType.StoredProcedure;
string productid = HttpContext.Current.Request.QueryString["productid"];
cmd.Parameters.Add(new SqlParameter("productid", SqlDbType.NVarChar)).Value = productid;
con.Open();
SqlDataReader reader = cmd.ExecuteReader();
reader.Read();
ProductDetails pro = new ProductDetails(
(string)reader["ProductID"], (string)reader["Description"], (string)reader["Image"]);
reader.Close();
return pro;
}
}
protected void PopulateControls()
private DataAccess da = new DataAccess();
{
ProductDetails product = da.GetProductDetails();
if (product.Description == String.Empty)
{
lblDescription.Visible = false;
}
else
{
lblDescription.Text = product.Description;
}
}
In the last piece i want to check if the Description field is null or empty in order to hide the label control but i get an error if i write: if (product.Description == DBNull.Value) and can only use ring.Empty. But i want to check for NULL values as well..
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Apr 4, 2011
So I took over this project and one page is throwing a lot of errors. I would need to refactor the whole thing but as always time is an issue.
In one case the code check's whether a datareader has any rows and if not go to an error page. However as the code is now the datareader can be null (didn't successfully connect to db) and in those cases I can't use
if (!dr.HasRows)
//
becasuse it obviously gives me 'nullreferenceexception was unhandled by code'. I tried with !dr.Read but same thing.
A part of the code is something like
SqlDataReader dr = null;
try
{
//connect to db etc
dr = DbHelper.GetReader("sp_GetCustomer", param);
}
catch
{
//show an error message
}
// and then:
if (!dr.HasRows)
{
}
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Nov 15, 2010
I'm having a method that exports content from the database to excel files. The method taks as paramaters a DataReader param and a int param - the number of rows. For the number of rows i'm using a dataset, wich i fill using the same query as for the datareader. So I'm executing it twice... Is there a way I can avoid that? get the number of rows from the datareader?
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Jul 28, 2010
I am getting an error that an open DataReader associated with this Command, when I'm not using datareader(though probably executereader() is the same thing) how would I close this if I don't have a datareader present?
using (SqlConnection conn = new SqlConnection(ConnectionString))
{
SqlCommand cmd = new SqlCommand("spSelectAllTypes",conn);
cmd.CommandType = CommandType.StoredProcedure;
[code]...
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Mar 29, 2011
var pq = attributes.SingleOrDefault(a => a.AttributeName == PasswordQuestion").AttributeValue;
The above code will throw an error if null. What is the best way to handle this?The below code would work, but I can't help but feel there's a more graceful way?
var pq = (attributes.SingleOrDefault(a => a.AttributeName == "PasswordQuestion") != null) ? attributes.SingleOrDefault(a => a.AttributeName == "PasswordQuestion").AttributeValue : null;
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Oct 21, 2010
I know for a fact that the SQL statement below returns NULL but my code statement "if (obj != null)" is not working.When I debug it I see a value of {} ... not sure what that is. Here is my code:
[Code]....
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Feb 11, 2010
I have Sub that requires EventArgs as below.
Sub Testing(ByVal sender As Object, ByVal e As EventArgs)
If I want to call the Sub from PageLoad event, I wrote like this Testing(nothing,nothing)
Then, in the Sub, I would like to check If Argment is Nothing or not
Dim testID As String
If (CType(sender, LinkButton).CommandArgument) = Nothing
testID=Request.QuerySting("myID")
ELSE
testID=(CType(sender, LinkButton).CommandArgument).ToString
End If
I get Null error at if statement (If (CType(sender, LinkButton).CommandArgument) = Nothing)
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Apr 4, 2011
How do you check for null with HtmlAgilityPack? I'm getting "Property or indexer 'HtmlAgilityPack.HtmlNode.HasChildNodes' cannot be assigned to -- it is read only" with the following.
if (Node.Element("TD").HasChildNodes = DBNull.Value)
I"m getting "Object reference not set to an instance of an object. " with
if (Node.Element("TD").HasChildNodes)
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Aug 27, 2013
If i have a page in which I want to check whether session is null.
If it is null it will redirect to other page.
But i also have a if (!Page.IsPostBack)
so i will check the session inside this if (!Page.IsPostBack) or outside it?
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Jan 26, 2011
How can i check if an output parameter is null before i bind it to a asp literal, and if it is null i want to just make the literal
hname1.Text = cmd.Parameters("@hotel1").Value
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[code]...
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Aug 17, 2010
I have set the value of an int parameter to the attribute of a textbox.The textbox can be empty or null, how to check whether the parameter is empty or null?
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Mar 28, 2011
Actually i have a table with 7 columns
1) Title varchar(100)
2)Description varchar(300)
3)ProfilePicture varbinary(max)
4) Image1 varbinary (max)
5)Image2 varbinary(max)
6)Image3 varbinary(max)
7)Image4 varbinary(max)
Image1,2,3,4 are not a mandatory fields so, when i inserted, i check it if it is not there then i insert null value, Now problem is when i retrive them if there is a row contain image1,2 are image content and 3,4 are null values dataset also filling as it is in database but when i checking like
[code]....
it shows error like
Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.
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Feb 4, 2011
Inside a function I need to check to see if a variable value is null, how to do this? I implemented the code but its not returning the value I thought it would return.If it's null I want to set the value of the variable, else I want to query the value from a table
[Code]....
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Mar 12, 2011
Right now I have an error if f.ParentID is null:
DataSet1.TreeItemRow[]
TreeItemRows = (from f
in tidt
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Jun 25, 2012
How to check the query string value null, if null then display the default value instead of object reference error.
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May 28, 2010
I'm experimenting with validating forms in the asp.net MVC framework. I'm focusing on server side validation for the time being. I've come across an error that I'm not sure how to rectify. System.NullReferenceException: Object reference not set to an instance of an object. The code that throws the error is:
[AcceptVerbs(HttpVerbs.Post)]
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{
mc.Modules = ModuleListDataContext.GetModuleList();
ViewData.Model = mc;
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//
//
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//
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Jan 28, 2010
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how I can change my query to accommodate this?
[Code]....
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Jun 4, 2010
[Code]....
but if table is empty i.e. there is no record for Store_no=storeno then it bill_id = (Convert.ToInt32(reader[0]) + 1); give a Null exception.
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i.e. How to check that reader[0] is null
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{
j.id,
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where a.job.id == j.id
select a.amount ).Sum(),
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j.completed
};
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Apr 7, 2010
I'm using LINQ together with XDocument to read a XML File. This is the code:XDocument xml = XDocument.Load(filename);
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{
[code]...
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Nov 17, 2010
I'm fetching som data from AD and I notice that I'm getting an exeption and notice that one of the users field that I'm fetching is empty, how can I prevent exeption.
Here is the code:
[Code]....
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Aug 20, 2010
What is the proper way to check for null or empty strings on dynamic objects? This is the only solution I've found so far:
if (admin.PasswordHash.GetType() == typeof(DBNull) || admin.PasswordHash == string.Empty)
If the field is null, the object returned is DBNull.Value, but if the field is empty string, it's return as a System.String object. This makes it impossible to do regular "admin.PasswordHash == DBNull.Value" check, as that will fail whenever the field has been set to empty string. Is my example the right (and only) way to go?
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Oct 6, 2010
How i do check whether DateTime data type variable is null/empty in asp.net ?
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Mar 14, 2012
this is my sql query and its work fine in my code but it only check ParentDeptID IS NULL it not working when ParentDeptID field is empty how can i check it
("select DeptID,DeptName,(select count(*) FROM HrDept " _
& "WHERE ParentDeptID=sc.DeptID) childnodecount FROM HrDept sc where ParentDeptID IS NULL ", _
objConn)
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