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Is it generating code at runtime? If yes then CodeDom or Reflection will help.
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No, that is not possible.
Try to ask about what it is that you want to accomplish, instead of asking about how you think that it should be solved.
Despite everything, the person most likely to be fooling you next is yourself.
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Last year, MikeinNH wrote an outstanding article on how to allow runtime SQL queries from form objects:
http://www.codeproject.com/KB/database/TableAdapter.aspx?display=Print
This almost all works for me except when I try to match database DateTime values. It doesn't act like any of the other variables and never finds a match. I don't think the problem is in SQL, I think it's in VB. My "Start Date Time" logic is below. Ideally, I'd like to use a between clause (eg. Between 'sdt' and 'edt') to make user records searchable in a time window that they choose.
Dim sdt As String = (sdtBox1.Text)
If sdt <> "" Then
stWhere = "DateTime > '" + sdt + "%' "
Else
The sdtBox1 value I'm testing with is '8/14/2008 00:00:00:001' and I can see that verbatim on a message box output, it just won't work in the SQL query. Is there a conversion or something that I need to do? Thanks
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Just quickly looking at your code - it looks like the text date format is fine. What is the '%' for though? I think that would cause the query to error off. If you were using a LIKE statement maybe, but not a >.
Open up SQL profiler when your VB code runs and see the exact statement being sent into SQL. Paste that query in QA/ SQL Manager to see the results.
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Right you are. I copied that from a LIKE statement.
When I removed the %, it still ignores my DateTime conditions, but I will check profiler to see what's happening.
Thanks.
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Change "DateTime > '" + sdt + "%' "
to: " DateTime > '" + sdt + "%' " space added to the front. The where clause may have been all jumbled together.
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Tried that, watched Profiler:
VB still didn't send that clause. It took my hardcoded front half ("Select From Where") plus the following AND condition successfully. But completely skipped DateTime.
I will keep playing with it, as long as it isn't an issue with text conversion or a DBDateTime property, then it's probably a syntax or logic error.
Thanks again for your help.
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>>VB still didn't send that clause. It took my hardcoded front half ("Select From Where") plus the following AND condition successfully. But completely skipped DateTime.
Ok. it sounds like your doing everything right.
Last ditch effort: put a breakpoint on the FillByWhere function (assuming your following the article logic closely). Check the value on the WhereExp variable. What is the exact string after this line has run: "Me._commandCollection(0).CommandText += " WHERE " + WhereExp"?
That should be exactly what's being sent to the db. If the value is wrong there, press CTRL+L and go up the call stack to see where the value is being excluded.
Good luck~!
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Yes! Thank you. I didn't know about SQL Profiler and since I've been watching that has pinpointed the problem. My textbox input data had an extra pair of ''s
Result:
SELECT * from Route_Call_Detail where RouterCallKeyDay > 148875 AND DateTime > ''2008-08-14 06:38:42.153''
It's corrected and I'm on my merry way.
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To whom ever can guide me a little on file stream usage.
I have a decent number of binary files that I must read only the first line of. Normally I declare a filestream as such (and use a binaryreader to use the filestream):
Dim fs As New FileStream(strFile(0), FileMode.Open, FileAccess.Read)
Is there a way to change the source file dynamically, or do I have to declare a new file stream for each file? The Name property is read only.
Thanks!
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Come fellow code project alumni - show thee the light!
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Try this...
Dim fs as FileStream
Dim FilesToProcess as New List(Of String)
FilesToProcess.Add("c:\test.txt")
FilesToProcess.Add("C:\boot.ini")
For Each fileToProcess as String in FilesToProcess
fs = New FileStream(strFile, FileMode.Open, FileAccess.Read)
'TODO: whatever you need to do with the file
Next 'filetoProcess
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You're still declaring a new FileStream for each file.
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no, just reallocating the one that has already been instantiated.
It sounded like he was trying to avoid doing this...
Dim fs1 as New FileStream(file1,blah, blah)
Dim fs2 as New FileStream(file2,blah, blah)
Dim fs3 as New FileStream(file3,blah, blah)
KissDzNutz, remember not to instantiate (Dim as New) inside the loop. Its less expensive to keep using the same ref.
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Initially your suggestion is what I was doing with in a for loop of the directories, but I changed the code as such (basic version, there is more work occurring after the last using with the byte array):
strEnum = strFile.GetEnumerator
While strEnum.MoveNext
Using fs As New FileStream(strEnum.Current.ToString, FileMode.Open, IO.FileAccess.Read)
Using br As New BinaryReader(fs)
bytLine = br.ReadBytes(55)
fs.Flush() : fs.Close()
br.Close()
End Using 'br
End Using 'fs
end while
What are the performance differences to using the above vs. fs = new file stream within the loop? For example, if the loop ran 20x, would there be 19 dead variables that .dispose can't be used on?
Also, since I'm being schooled today  , I have another dumb question regarding the "new" keyword for declaring new vars in a specific way.
For a simple example, creating the following string var is set up to *****
Dim strTest As String = "*****"
Creating the variable below accomplishes the same thing, but when you use the = New String part, does this actually create 2 string variables (meaning strTest and then a new string that is floating around in deep space)?
Dim strTest As String = New String(CChar("*"), 5)
Thanks! Always trying to learn...
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Eek... whoever taught you to use .GetEnumerator and MoveNext to iterate a string collection (array, or ListOf) should be shot. That, along with "If (Not Is Nothing)" is easily confusing and difficult for the next person to follow. For Loops are the way to go.
To answer your first question, Yes. You will have paid the setup, instantiation, and destruction costs 20x. You can call .Dispose() manually if you want to, but you are essentially discarding the memory to the GC by not using the object any longer.
When you declare a variable with "Dim obj as New Object()" (or with Using), you are basically allocating a chunk of memory and filling it (instantiation). The application will have to manage that object and clean up after it (Creation and Destruction), so each of the 3 operations (allocate / create, instantiate, destroy) has a resource cost.
If you declare a variable with "Dim obj as Object", you are only doing the allocation of memory. You can then re-use that referenced memory (obj = New Object()) to repeatedly instantiate objects and only pay the Creation cost 1x. Yes you will still have to pay instantiation and destruction costs, but this will save you some cost.
This works for reference types, since value types are created right on the heap I dont think it makes a lick of difference.
Strings are immutable, which means that each change creates more memory.
Dim str1 as String = "abc" 'one object in memory
Dim str2 as String = str1 + "def" 'now there are 3 objects in memory. str1, "def", and str2.
This is why they made StringBuilder classes. These are able to properly append and not make so many objects in memory.
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Thanks for the responses.
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No. You are only declaring one strFile and re-using it like I explained in the middle of the last post.
If you want, you can also do
For x as Integer = 0 to strFiles.Length -1
'do operations with strFiles(x)
Next 'x
Strings being immutable refers to the fact that they cannot be changed. New ones are created and replace the last one.
1K strings is really not a lot and either method would work well. You will see object creation cost saving benefits when dealing with larger and more complex objects (like Streams/ UI Controls, iTextSharp PDF objects).
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Just a couple small things I have wondered about and never really found concrete answers for.
Thanks for taking the time and giving full explanations.
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I want to connect to an access database using vb.net. Can someone kindly assist with the codes to do this, including the declaration codes as well. I want to connect using codes and not the datagrid.
Thank you! 
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There is nice tutorial available here
Please remember to rate helpful or unhelpful answers, it lets us and people reading the forums know if our answers are any good.
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have a look at www.connectionstrings.com
Bob
Ashfield Consultants Ltd
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Thanks Bob for that response. That is a good site.
Please take a look at this code:
<Dim db as NEW ADO DB.Connection
Dim rs as NEW ADO DB.Record-set
DIM spath as String ' Path for the database
Dim SQLL as String ' Sql statement
sPath = app.path & "\DB\Name.mdb
>
Now the question is Bob: Is this code sufficient for connecting to an access DB? If not what is lacking?
Thank you!
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i installled a window service that will access ftp server folder.
i get the following error The remote server returned an error: (500) Internal Server Error.. any idea pls
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