How can I add a scalar variable for an SQL command In a function that doesn't house my query directly?

Question

I will try to keep this as brief as possible.

I have a function called GetData(ByVal query As String) whose sole purpose is to populate a data table multiple times based on certain conditions. As you can see, the function accepts a string variable where the SQL statement resides. What I am trying to do is add a scalar variable, "@date" in my case, and no matter where I try to add this variable it throws an error stating "Must declare scalar variable @date.

Edit: I should mention that it is throwing the "must declare variable" error on the sda.Fill(dt) line.

GetData Function

    Private Shared Function GetData(ByVal query As String) As DataTable
        Dim constr As String = ConfigurationManager.ConnectionStrings("WarrantyConnectionString").ConnectionString
        Using con As SqlConnection = New SqlConnection(constr)
            Using cmd As SqlCommand = New SqlCommand(query)
                Dim dt As DataTable = New DataTable()
                cmd.Parameters.Add("@date", SqlDbType.Date).Value = Date.Today
                Using sda As SqlDataAdapter = New SqlDataAdapter(query, con)
                    cmd.Parameters.AddWithValue("@date", Date.Today)
                    sda.Fill(dt)
                End Using

                Return dt
            End Using
        End Using
    End Function

I am calling the function in a procedure that has the query and handles all of the conditions I need.

Procedure

Dim queryStart As String = "SELECT ( SELECT SUM(DealerNet) FROM Agreement WHERE VoidDate IS NULL "
        Dim queryAlias As String = "AS Actual, "
        Dim queryStart2 As String = "(SELECT SUM(Amount) FROM AccountingUS.dbo.ProjectedSales "
        Dim queryAlias2 As String = "AS Projected "

        If chart = "pmtd" Then
            Dim queryCondition As String = "AND IssueDate BETWEEN (SELECT DATEADD(MONTH, DATEDIFF(MONTH, 0, @date)-1, 0)) AND @date) "
            Dim queryCondition2 As String = "WHERE [Month] = MONTH(@date) AND [Year] = YEAR(@date)) "
            Dim query As String = queryStart + queryCondition + queryAlias + queryStart2 + queryCondition2 + queryAlias2
            Dim xMember1 As String = "Actual"
            Dim xMember2 As String = "Projected"

            Dim dt As DataTable = GetData(query)
            pmtdChart.DataSource = dt

The variable in question is the @date variable in the strings within the "If" statement, the only value it holds is todays date. Currently, I have tried to use "cmd.Parameters.Add("@date", SqlDbType.Date).Value = Date.Today in the GetData function, however, I still receive the same "Must declare scalar variable" error. I have also tried replacing the @date variable with simply "" + Date.Today + "" or a variable that holds todays date, but upon doing so I receive an operand error about "Operand Clash: Date is incompatible with Int"

Any help regarding this issue would be greatly appreciated, I am relatively new to programming and would appreciate any tips or criticisms regarding best practices. If you need any additional information or clarification regarding this issue I would be happy to provide what I can. Thank you in advance.

Answer 1

If you look closely, you setup a cmd command, but you never actually pass it to the DataTable. So it doesn't know anything about your params. How about this instead (copied untested from Trying to pass SqlCommand in SqlDataAdapter as parameters):

DataTable dt = new DataTable();
using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings("WarrantyConnectionString").ConnectionString))
            {
                con.Open();
                using (SqlCommand cmd = con.CreateCommand())
                {
                    cmd.CommandText = query;
                    cmd.CommandType = CommandType.Text;
                    cmd.Parameters.Add("@date", SqlDbType.Date)
                    cmd.Parameters.AddWithValue("@date", Date.Today)
                    using (SqlDataAdapter adp = new SqlDataAdapter(cmd))
                    {
                        adp.Fill(dt);
                        return dt;
                    }
                }
            }

Answer 2

    Dim dt as new DataTable()
    using db as new SqlConnection(ConfigurationManager.ConnectionStrings("WarrantyConnectionString").ConnectionString)
        db.Open();
        using cmd as New SqlCommand(query, con)
            cmd.Parameters.Add("@date", SqlDbType.Date).value = Date.Today
            //cmd.Parameters.AddWithValue("@date", Date.Today)
            using adp as new SqlDataAdapter(cmd)
                adp.Fill(dt)
                return dt
            End using
        End using
    End using

Answer 3

Ok, a few things:

I would actually pass a command object to that get data routine.

And your issue is you feeding the query to the "adaptor", but NOT supplying the @date parameter to that "sda"

this:

   Using sda As SqlDataAdapter = New SqlDataAdapter(query, con)
      cmd.Parameters.AddWithValue("@date", Date.Today)
      sda.Fill(dt)
   End Using

In other words, you NOT EVEN using the cmd object!!!

So, you would need to add the parameter's to the sda object!!

eg this:

Public Function GetData(ByVal query As String) As DataTable

    Dim dt As DataTable = New DataTable()

    Dim constr As String =
        ConfigurationManager.ConnectionStrings("WarrantyConnectionString").ConnectionString

    Using con As SqlConnection = New SqlConnection(constr)
        Using sda As SqlDataAdapter = New SqlDataAdapter(query, con)
            sda.SelectCommand.Parameters.Add("@date", SqlDbType.Date).Value = Date.Today()
            sda.Fill(dt)
        End Using
    End Using

    Return dt

End Function

So, yes, you WILL get that error about "@date" not being declared, since you NOT using the cmd object to fill the table, but are using the data adaptor.

So, as a future suggest?

Pick one way, or the other way.

I MUCH over the years have decided that I will use/have/adopt and cookie cut over and over the SqlCommand object.

I find the Sql cmd object better, since:

it has the parameters.
it has a connection object (if you want to use)
it has a data reader built in

So, what this means?

I suggest this code for get data:

Private Shared Function GetData(ByVal query As String) As DataTable
    Dim constr As String =
        ConfigurationManager.ConnectionStrings("WarrantyConnectionString").ConnectionString
    Dim dt As DataTable = New DataTable()

    Using con As SqlConnection = New SqlConnection(constr)
        Using cmd As SqlCommand = New SqlCommand(query, con))
            con.Open()
            cmd.Parameters.Add("@date", SqlDbType.Date).Value = Date.Today
            dt.Load(cmd.ExecuteReader)
        End Using
    End Using

    Return dt

End Function

So, we don't need a data adaptor. In fact, you only need a adaptor if you going to update the resulting table (think a "adaptive" table to remember this). You not going to update the data, so really, no need to use a "adaptor" at all here. (and sadly, far too many examples use a "adaptor" anyway. They are for ALLOWING update of the data table, and you not doing that!

So, use a command object. Do note that you ALWAYS must then open the confection, but since we have "using" blocks, it will ALWAYS be closed for you.

And note how then we don't create to "use" the "reader" from the adaptor, nor a fill command. (so, we eliminated one whole confusing object!!).

So, in your example, you created a SQL command object, correctly added the parameter to the command object, but THEN DON'T use it, and then decided to create a data adaptor, and use that!!!

So, you could/can leave your code as you had with the sda "prameter " fix I posted above.

However, but I think your better off to use a sql command object.

Note even better?

Pass the command object to the GetData routine.

I have a global "general" purpose routine called MyRstP(), and I pass it a command object, even for just plain jane sql.

but, if you decide to add parameter's, you can!

Do note that parameter's can be added 100% independent of the SQL string, and they can be added before, or after you set the sql string.

And you can add parameter's WITHOUT a valid working connection (or have created one just yet). So, "parameters" are just a colleciton - it does not care about the SQL (well, at least not yet!!).

So, here is my RstP, and I dumped this into a plain jane "module1" which VB has (this means you don't have to create a static class, and this works then just like VB6, or VBA.

So, this:

Public Function MyRstP(cmdSQL As SqlCommand, ByVal Optional strCon As String = "") As DataTable

    If strCon = "" Then
        strCon = My.Settings.TEST4
    End If

    Dim rstData As New DataTable
    Using conn As New SqlConnection(strCon)
        Using (cmdSQL)
            cmdSQL.Connection = conn
            conn.Open()
            rstData.Load(cmdSQL.ExecuteReader)
        End Using
    End Using

    Return rstData

End Function

So, now to say fill a grid view, I use this:

    Dim strSQL As String =
        "SELECT id, HotelName, City FROM tblHotelsA"

    Dim cmdSQL As New SqlCommand(strSQL)

    GridView1.DataSource = MyRstP(cmdSQL)
    GridView1.DataBind()

or say a given date of some such: How about all hotel visit dates from start of year.

So, this:

    Dim strSQL As String =
        "SELECT id, HotelName, City FROM tblHotelsA
        WHERE VisitDate >= @dtStart"

    Dim dtStart As DateTime
    dtStart = DateSerial(DateTime.Today.Year, 1, 1)

    Dim cmdSQL As New SqlCommand(strSQL)
    cmdSQL.Parameters.Add("@dtStart", SqlDbType.DateTime).Value = dtStart

    GridView1.DataSource = MyRstP(cmdSQL)
    GridView1.DataBind()

note then how I have that MyRstP (like your get data), but I can pass it quite much anything I want, including parameter's from the "calling" code, NOT in that general routine.

Anyway, the above use and adding the parameter's to the "adaptor" will fix this, but I would change over to using just a command object and a connection - the adaptor really not required, and as noted, they really are to be used WHEN you actually want to update the data table, and then send it back to the database in one shot.