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You are right. Access uses OleSaveToStream and OleLoadFromStream COM API calls to save/load objects. The CLSID of the stored object is stored prior to object's binary data.
The best solution I may recommend. Don't modify the data transferred from Access. If you are programming in C++ just pass the stream object to OleLoadFromStream function and it will do all job for you. If you are developing under VB, save stream to disk and use GetObject("pathname"), the object will be loaded automatically.
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I am new to database programming and am relatively ineperienced in C++ programming (have done most of my programming in Java). I have searched and searched for tutorials on how to do what I want to do and have had little luck. All I need to do is to read from a .dbf file that contains information about airports. This dbf file is stored locally on this PC and the PC runs Windows 2000. I need to develop a program that I can run on a number of different PC's running Windows 2000, each having it's own locally stored .dbf file. When I research database resources, I see ADO, DAO, ODBC, OLE DB etc... etc... and I cant seem to make any sense of any of it. I was wondering if some of you could help.
1) How should I get started? What class should I use?
2) Do you have any weblinks of some very simple to the point online tutorials that can help me along.
Any help would be appreciated
thanks
Kevin Shaffer
Student of Computer Science
University of Kansas
kshaff03@msn.com
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I think it is the maximum byte size of the field.
Bruce Duncan, CP#9088, CPUA 0xA1EE, Sonork 100.10030 Blackadder: Baldrick, have you no idea what irony is? Baldrick: Yeah, it's like goldy and bronzy only it's made of iron.
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Bruce Duncan wrote:
maximum byte size
Ok cool. I thought that's what it might be.
How would I determine the maximum amount of characters that can be stored in an nvarchar field, say of length 64?
Thanks
$TeVe McLeNiThAn
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A thought crossed my mind just as I posted my previous answer...
In Enterprise Manager, when you have an nvarchar type, with a length of 50, it means it can store 50 unicode characters, and therefore take up a maximum of 100 bytes. Hence, my previous answer is not entirely correct.
To answer your new question, an nvarchar field of length 64 can hold up to 64 unicode character, with a byte size of up to 128 (+ minimal overhead I guess)
Bruce Duncan, CP#9088, CPUA 0xA1EE, Sonork 100.10030 Blackadder: Baldrick, have you no idea what irony is? Baldrick: Yeah, it's like goldy and bronzy only it's made of iron.
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Thanks. That helps.... I didn't want to make fields too short nor too big;)
$TeVe McLeNiThAn
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Cheers, glad to help
Bruce Duncan, CP#9088, CPUA 0xA1EE, Sonork 100.10030 Blackadder: Baldrick, have you no idea what irony is? Baldrick: Yeah, it's like goldy and bronzy only it's made of iron.
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I have a situation whereby I need to modify a base query with an unknown number of additional restraints which are themselves held in a reference table. How would I go about this?
For example the reference table might hold:
"user_name <> 'default'"
"policy_no > 20000"
etc.
and my stored proc needs to add these conditions to its select operation. Ideas?
'--8<------------------------
Ex. Datis:
Duncan Jones
http://www.merrioncomputing.com
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I'm assuming you're using SQL Server.
Look up the sp_executesql system stored proc or the EXECUTE ( ) statement, both will let you execute a statement contained within a varchar variable.
Bruce Duncan, CP#9088, CPUA 0xA1EE, Sonork 100.10030 Blackadder: Baldrick, have you no idea what irony is? Baldrick: Yeah, it's like goldy and bronzy only it's made of iron.
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I'm using Sybase XI - but I'm sure there's an equivalent somewhere - but that'd mean I'd have to assemple the entire query as a varchar().
'--8<------------------------
Ex. Datis:
Duncan Jones
http://www.merrioncomputing.com
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Sorry, don't know anything about Sybase, but I would imagine it has something similar.
Maybe this is what you're looking for ?
How can I execute dynamic SQL with ASE?[^]
Bruce Duncan, CP#9088, CPUA 0xA1EE, Sonork 100.10030 Blackadder: Baldrick, have you no idea what irony is? Baldrick: Yeah, it's like goldy and bronzy only it's made of iron.
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Okay... c# winforms ado.net
Can i size up columns using the resource editor thing?
Ahead of time before the app starts and forces the user
to resize all the columns each time?
And how do I hide a column?
Thanks.
...Steve
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Dear friends,
I have an application developed in VC++ and it makes an active connection to SQL server using ADO. My application issues queries and in return SQL server sends me results.
Is it possible that SQL server 'talk to my application' i.e what i want is that whenever any row of a table is changed in SQL server by some other entity, SQL server inform my application of this change. Is it possible??
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Hi..
Seems you need to create a trigger in SQL Server that call an Extended Stored Procedure (made in vc++ for example)
this Stored Procedure can store a shared variable that your Application checks for it..
You can create a worker thread that is blocked until this variable changes and unlocked by the Extended Stored Procedure...
Anyway .. I love the idea of making SQL server talks to your Application..
tell us about any progress
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I'm new to c#, winforms and ado.net, so bear with me.
I've got a dumb lil checkbook table. I don't WANT to have an identity
column for a primary key, but i do to help out ado.net...
So I get SqlConnection, DataSet, and SqlDataAdapter's Fill/Update.
I haven't really messed much with the DataGrid, but got somethin goin on.
And I need help with the properties of this frassin brassin adapter.
I've been thru the adapter wizard, but hate the mess it leaves.
I know about the commandbuilder a bit, but don't know when it's needed
and when not.
1) c# to hide the dang identity column in my datagrid is?
2) can I lose the identity column? implications are?
3) What's the deal with the SqlDataAdapter properties???
I guess tackin on a CommandBuilder is easiest, but you gotta have
a single primary key, right?
Otherwise, what do I do to fill in the sel/ins/upd/del command props?
Thanks VERY much for ANY help
...Steve
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Hi folks,
From a dataset (generated by Data.SqlClient rather than Data.OleDb) can I determine the original SQL Datatype? I am trying to determine if a field is Currency vs. a straight decimal. It seems that the "datatype" property of the datacolumn object return decimal for both SQl currency and SQL decimal.
Thanks
Tom K.
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Hi, all,
I am very close to finish my first .NET application( C#, Winform Datagrid, and MS Access database). I can modify all the data in my DataSet on my winform datagrid. NowI am trying for the first time to save the data back to my Access DB. When I call daMyDataAdaptor.Update( for a single table), I got this attached error. It says the UPDATE statement has syntax error, but the Statement was created by the wizard when I configured DataAdaptor, how can it be wrong? I know this must be something I missed, Please help.
Due to size limitation of the attachment, I can not attach the small test program. If you can help me, I can sent you the zip test program.
Code on Save button as follows:
------------------------------------
if ( connMain.State != ConnectionState.Open )
{
connMain.Open();
}
System.Data.OleDb.OleDbTransaction trans = connMain.BeginTransaction();
daTaskList.UpdateCommand.Transaction = trans;
try
{
daTaskList.Update(dsMain1, "LMTaskList");
//System.Exception MyErr = new System.Exception("Error Occurred");
//throw(MyErr);
trans.Commit();
}
catch(System.Exception err)
{
trans.Rollback();
MessageBox.Show("Failed to save Available Tasks!\n" + "Details: " + err.ToString() );
}
finally
{
connMain.Close();
}
-----------------------------------------------------
I wonder what is wrong with the code I have.
Thanks again.
Dion
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What was the error message that you got?
What SQL Insert/Update/Delete statements were you using?
Andy Harman
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After about a day, I finally figured out what is wrong. In my DB table, I have a column called "Value". It caused the crash.
Thanks anyway.
Dion
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Hi,
I am developing a simple WinForm app with datagrid on the form. I want to know when any cell text changed so that I can enable my Save button. What event should I handle? Any example will be even better. Thanks.
Dion
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I'm creating a simple Access Database with one table and one boolean field via ADOX and Jet Oledb Provider.
The following code gives me an IDispatch Error 3105 when appending the Table. Note that with adInteger or adVarWChar the code is working. Any idea ? Thx in advance.
pThisAdoCatalogPtr.CreateInstance(__uuidof(Catalog));
pThisAdoTablePtr.CreateInstance(__uuidof(Table));
pThisAdoColumnPtr.CreateInstance(__uuidof(Column));
pThisAdoCatalogPtr->Create("PROVIDER=Microsoft.Jet.OLEDB.4.0;Jet OLEDB:Engine Type=4;Jet OLEDB:System Database=c:\\MsOffice\\Access\\System.mdw;Data Source=mybase.mdb;User Id=admin;Jet OLEDB:Database Password=mypass;");
pThisAdoTablePtr->Name="MyTable";
pThisAdoColumnPtr->Name="BooleanColumn";
pThisAdoColumnPtr->Type=adBoolean;
pThisAdoColumnPtr->Attributes=adColNullable;
pThisAdoTablePtr->Columns->Append(_variant_t((IDispatch *)pThisAdoColumnPtr), adBoolean, 0);
pThisAdoCatalogPtr->Tables->Append(_variant_t((IDispatch *)pThisAdoTablePtr)); <--- Here is the exception thrown.
Bruno.
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Hiya I have an MFC app that writes data to my SQL database. The columns lenghts are set to 30. But when I open my SQL database to view the contents, I can only see the first 15 chars of each column..
How do I get the SQL database to display the full columns lenghts when it is opened??
Thanks,
grahamoj.
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Are you passing spaces at the end of the values at all, is it 30 characters of data, could you be trimming the values?
-Nick Parker
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