Hi,

I'm wanting to write an in memory ADO.Net Datatable to a
worksheet
in an Excel spreadsheet. If the worksheet exists I would like to
overwrite all the existing data in the worksheet.

I've successfully used the Jet OLE DB Provider to create a new Excel
worksheet (using a CREATE TABLE) and populate it. But I haven't been
able to overwrite data in an existing worksheet.

In an old posting (Oct 2002) to microsoft.public.data.ado (Subject:
Delete records in Excel with ADO from VB) it was mentioned that Excel
automation is needed to delete empty rows cleanly. But it also
mentioned
that you can execute a DROP TABLE and start over.

I have tried using DROP TABLE which deletes all the data in a worksheet,
however it also seems to delete the column headers which means when I
use the InsertCommand on an OleDbDataAdapter to write the dataTable to
Excel no data gets written.

I was hoping DROP TABLE would actually delete the worksheet (rather than
just it's contents) so that I could then re-create the worksheet (using
CREATE TABLE).

Question :
------------
Am I doing something wrong with my InsertCommand, or is there some way
I can delete the worksheet itself or delete the contents of the
worksheet and still leave the column headers intact ?

I would like to avoid using Excel automation if possible, since if I
don't use it Excel does not need to be installed, versioning issues can
be avoided and I presume that using the Jet OLE DB Provider is faster
than using automation.

Thanks in advance,
Joel Gordon.

Hi

I reviewed the thread and find that there is a similar issue in the
newsgroup below.Now I have replied to you, you may go and take a look.
Subject: Overwriting existing data in an Excel worksheet using ADO.Net
Newsgroups: microsoft.public.excel.programming

Best regards,

Peter Huang
Microsoft Online Partner Support

Get Secure! - www.microsoft.com/security
This posting is provided "AS IS" with no warranties, and confers no rights.

"Joel Gordon" wrote ...

I've successfully used the Jet OLE DB Provider to create a new Excel
worksheet (using a CREATE TABLE)

Not quite correct. You cannot directly create a worksheet using the
OLE DB provider or Excel ODBC driver e.g. (the $ suffix indicates the
Excel 'table' is a worksheet):

CREATE TABLE [Sheet99$] (Col1 FLOAT);

will generate an error, ' 'Sheet99$' is not a valid name because the $
character is illegal in the name for a 'named range'.

You can only directly create a 'named range' (technically a workbook
level defined Name that is defined using a simple formula that returns
a Range object). Try a legal name e.g.

CREATE TABLE Sheet99 (Col1 FLOAT);

and it works without error assuming the a 'named range' does not
already exist. The provider/driver will create a new worksheet to host
the new 'named range', unless a worksheet of the same name already
exists and is unused. If the sheet exists and is 'used' the new sheet
will be given a name derived from the 'named range' name e.g.
Sheet991.

So you can create a worksheet using the provider/driver but only as a
by-product of creating a 'named range' and then only if the
circumstances are favorable.

You *can* use the DROP syntax with a worksheet e.g.

DROP TABLE [Sheet99$];

This will clear the worksheet including the column headers but it will
not remove the worksheet nor any 'named range' of the same name - the
latter will be redefined to refer to the range in the top left corner
e.g. =Sheet99!$A$1:$A$1. Because the 'named range' is retained, a
subsequent CREATE TABLE using the same table name will fail.

You can also use the DROP syntax with a 'named range' e.g.

DROP TABLE [Sheet99];

this will do the same as DROP on the worksheet name but additionally
remove the defined Name, allowing a subsequent CREATE TABLE to work
and be created on the same worksheet.

Jamie.

--

Jamie Collins wrote:

"Joel Gordon" wrote ...

I've successfully used the Jet OLE DB Provider to create a new Excel
worksheet (using a CREATE TABLE)

Not quite correct. You cannot directly create a worksheet using the
OLE DB provider or Excel ODBC driver e.g. (the $ suffix indicates the
Excel 'table' is a worksheet):

CREATE TABLE [Sheet99$] (Col1 FLOAT);

will generate an error, ' 'Sheet99$' is not a valid name because the $
character is illegal in the name for a 'named range'.

You can only directly create a 'named range' (technically a workbook
level defined Name that is defined using a simple formula that returns
a Range object). Try a legal name e.g.

CREATE TABLE Sheet99 (Col1 FLOAT);

and it works without error assuming the a 'named range' does not
already exist. The provider/driver will create a new worksheet to host
the new 'named range', unless a worksheet of the same name already
exists and is unused. If the sheet exists and is 'used' the new sheet
will be given a name derived from the 'named range' name e.g.
Sheet991.

So you can create a worksheet using the provider/driver but only as a
by-product of creating a 'named range' and then only if the
circumstances are favorable.

You can use the DROP syntax with a worksheet e.g.

DROP TABLE [Sheet99$];

This will clear the worksheet including the column headers but it will
not remove the worksheet nor any 'named range' of the same name - the
latter will be redefined to refer to the range in the top left corner
e.g. =Sheet99!$A$1:$A$1. Because the 'named range' is retained, a
subsequent CREATE TABLE using the same table name will fail.

You can also use the DROP syntax with a 'named range' e.g.

DROP TABLE [Sheet99];

this will do the same as DROP on the worksheet name but additionally
remove the defined Name, allowing a subsequent CREATE TABLE to work
and be created on the same worksheet.

Jamie.

--

Hi Jamie,

Thanks for the reply and for clarifying worksheets and named ranges
- I certainly had not understood the differences.

I agree with how you have described the behaviour regarding creating
tables and how this relates to the creation of worksheets and named
ranges BUT...

When I try to drop the table with a 'named range' it does NOT seem to
remove the defined name, hence a subsequent CREATE TABLE does NOT work
- I get an OleDbException stating that the table already exists.

Following is the code I am using. The first time the code is run (and
the excel file does not exist) it runs fine. If it is run again then
the drop table leaves the named range alone and hence the create table
fails.

I am using Microsoft Office Excel 2003 (11.6355.6360).

Am I doing something wrong ?

Thanks,
Joel.

internal static void WriteToExcelFile( DataTable dataTable,
string excelFileName ) {
OleDbConnection connection =
new OleDbConnection( "Provider=Microsoft.Jet.OLEDB.4.0;" +
"Data Source=" + excelFileName + ";" +
"Extended Properties=\"Excel 8.0;HDR=Yes\"" );
if ( File.Exists( excelFileName ) ) {
connection.Open();
if ( TableExists( connection, dataTable.TableName ) ) {
DeleteTable( connection, dataTable.TableName );
}
connection.Close();
}
WriteDataTable( dataTable, connection, excelFileName );
}

private static bool TableExists( OleDbConnection connection,
string tableName ) {
DataTable table =
connection.GetOleDbSchemaTable( OleDbSchemaGuid.Tables,
new object[] {null, null, null, "TABLE"} );
foreach( DataRow dataRow in table.Rows ) {
if ( ((string)dataRow["TABLE_NAME"]) == tableName ) {
return true;
}
}
return false;
}

private static void DeleteTable( OleDbConnection connection,
string tableName ) {
OleDbCommand command =
new OleDbCommand( "DROP TABLE [" + tableName + "]",
connection, null );
command.ExecuteNonQuery();
}

private static void WriteDataTable( DataTable dataTable,
OleDbConnection connection,
string fileName ) {
connection.Open();
try {
// Create workbook with appropriate column headers
OleDbCommand command = new OleDbCommand(
GetCreateString( dataTable ), connection, null );
command.ExecuteNonQuery();

// Populate worksheet with all data from the dataTable
OleDbDataAdapter adapter =
new OleDbDataAdapter("SELECT * FROM
["+dataTable.TableName+"]",
connection );
OleDbCommandBuilder builder = new OleDbCommandBuilder(adapter);
builder.QuotePrefix = "[";
builder.QuoteSuffix = "]";
adapter.Update( dataTable );
} finally {
connection.Close();
}
}

private static string GetCreateString( DataTable table ) {
string createString = "CREATE TABLE [" + table.TableName + "](\n";
foreach( DataColumn column in table.Columns ){
createString += "[" + column.ColumnName + "] ";
switch( column.DataType.ToString() ){
case "System.String":
createString += "TEXT";
break;
case "System.Int32":
createString += "INT";
break;
case "System.Double":
case "System.Single":
createString += "FLOAT";
break;
case "System.DateTime":
createString += "DATETIME";
break;
default:
throw new ApplicationException( "Unknown type." );
createString += ",\n";
}
createString = createString.TrimEnd( new char[]{'\n',','} );
createString += ");";
return createString;
}

"Joel Gordon" wrote ...

The first time the code is run (and
the excel file does not exist) it runs fine. If it is run again then
the drop table leaves the named range alone and hence the create table
fails.

I don't think that is correct. I think your code is failing to call
its DeleteTable method on the second pass because it wrongly assumes
the table doesn't exist.

You are using GetOleDbSchemaTable to detect whether the table exists
and only try to drop the table if TableExists returns true. However, a
'named range' that contains no data rows does not show up as a table
in the schema (non-.NET readers should note that the same behaviour
results when using GetOpenSchema in ADO 'classic'). Regardless, the
table may still be used and so, of course, may be dropped.

The approach I usually take is to try to DROP the table anyhow: if it
exists then it gets dropped; if it doesn't exist I ignore the error.

Jamie.

--

Jamie Collins wrote:

"Joel Gordon" wrote ...

The first time the code is run (and
the excel file does not exist) it runs fine. If it is run again then
the drop table leaves the named range alone and hence the create table
fails.

I don't think that is correct. I think your code is failing to call
its DeleteTable method on the second pass because it wrongly assumes
the table doesn't exist.

You are using GetOleDbSchemaTable to detect whether the table exists
and only try to drop the table if TableExists returns true. However, a
'named range' that contains no data rows does not show up as a table
in the schema (non-.NET readers should note that the same behaviour
results when using GetOpenSchema in ADO 'classic'). Regardless, the
table may still be used and so, of course, may be dropped.

The approach I usually take is to try to DROP the table anyhow: if it
exists then it gets dropped; if it doesn't exist I ignore the error.

Jamie.

--

Thanks Jamie - you are correct. I have changed my code to always attempt to
DROP the table. Unfortunately when I attempt to write the data table to a
workbook which has had a successful DROP table done then I get the exception :

System.InvalidOperationException: Dynamic SQL generation for the UpdateCommand
is not supported against a SelectCommand that does not return any key column
information.

A complete example of my code follows. Creation of a new excel file works fine
but attempting to overwrite existing data fails with the exception above.

What am I doing wrong?

Thanks again,
Joel.


using System;
using System.IO;
using System.Data;
using System.Data.OleDb;

public class TestWriteToExcel {

const string EXCEL_FILENAME = @"C:\TestWorkBook.xls";

public static void Main() {
try {
if ( File.Exists( EXCEL_FILENAME ) ) {
File.Delete( EXCEL_FILENAME );
}
DataTable dataTable = CreateDataTable();
dataTable.TableName = "TestWorkSheet";
WriteToExcelFile( dataTable, EXCEL_FILENAME );
dataTable.Rows[0][0] = 999;
WriteToExcelFile( dataTable, EXCEL_FILENAME );
} catch ( Exception e ) {
Console.WriteLine( e );
}
}

private static DataTable CreateDataTable() {
DataTable dataTable = new DataTable();
dataTable.Columns.Add( "IntColumn", typeof(Int32) );
for( int i=1; i<4; i++ ) {
DataRow row = dataTable.NewRow();
row[0] = i;
dataTable.Rows.Add( row );
}
return dataTable;
}

static void WriteToExcelFile( DataTable dataTable,
string excelFileName ) {
OleDbConnection connection =
new OleDbConnection( "Provider=Microsoft.Jet.OLEDB.4.0;" +
"Data Source=" + excelFileName + ";" +
"Extended Properties=\"Excel 8.0;HDR=Yes\"" );
connection.Open();
try {
// Clear worksheet
DeleteTable( connection, dataTable.TableName );

// Create worksheet
OleDbCommand command = new OleDbCommand( GetCreateString(dataTable),
connection, null );
command.ExecuteNonQuery();

// Populate worksheet all data from dataTable
OleDbDataAdapter adapter = new OleDbDataAdapter(
"SELECT * FROM [" + dataTable.TableName + "]", connection );
OleDbCommandBuilder builder = new OleDbCommandBuilder( adapter );
builder.QuotePrefix = "[";
builder.QuoteSuffix = "]";
adapter.Update( dataTable );
} finally {
connection.Close();
}
}

static void DeleteTable( OleDbConnection connection, string tableName ) {
try {
OleDbCommand command =
new OleDbCommand( "DROP TABLE [" + tableName + "]",
connection, null );
command.ExecuteNonQuery();
Console.WriteLine( "Table " + tableName + " dropped." );
} catch (Exception) {
;
}
}

static string GetCreateString( DataTable table ) {
string createString = "CREATE TABLE [" + table.TableName + "](\n";
foreach( DataColumn column in table.Columns ){
createString += "[" + column.ColumnName + "] ";
switch( column.DataType.ToString() ){
case "System.String":
createString += "TEXT";
break;
case "System.Int32":
createString += "INT";
break;
case "System.Double":
case "System.Single":
createString += "FLOAT";
break;
case "System.DateTime":
createString += "DATETIME";
break;
default:
throw new ApplicationException( "Unknown type." );
}
createString += ",\n";
}
createString = createString.TrimEnd( new char[]{'\n',','} );
createString += ");";
return createString;
}
}

Joel Gordon wrote:

I have changed my code to always attempt to
DROP the table. Unfortunately when I attempt to write the data table
to a
workbook which has had a successful DROP table done then I get the
exception :

System.InvalidOperationException: Dynamic SQL generation for the
UpdateCommand
is not supported against a SelectCommand that does not return any key
column
information.

See:

PRB: Error Occurs When You Use ADO.NET OLEDbDataAdapter to Modify Excel
Workbook
http://support.microsoft.com/default...b;en-us;316756

Another 'resolution' to the problem us to write the dynamic SQL
yourself e.g. using Jet's INSERT INTO..SELECT syntax, perhaps using an
ODBC connection to the data source. Old technology yes, but then so is
Excel <g.

Jamie.

--