Develop Reference

To export Postgres DB to excel using c#

I need to export Postgres DB (having around 20 tables) to excel using C#. I need to implement some logic on the data from DB and then need to export it. Any idea of how to export all data using c#?

using Npgsql;
using OfficeOpenXml; // Nuget EPPlus
using System.IO;
EPPlus has a one-step method to export a data table into a spreadsheet, so if you leveraged this, you should be able to loop through your queries and export each one to a unique sheet.
Something like this (untested but should be 99% there) should do the trick:
FileInfo fi = new FileInfo("foo.xlsx");
ExcelPackage excel = new ExcelPackage(fi);
int sheet = 1;
foreach (string sql in sqlQueries)
{
DataTable dt = new DataTable();
NpgsqlCommand cmd = new NpgsqlCommand(sql, conn);
NpgsqlDataAdapter da = new NpgsqlDataAdapter(cmd);
da.Fill(dt);
ExcelWorksheet ws = excel.Workbook.Worksheets.Add(string.Format("Sheet{0}", sheet++));
ws.Cells["A1"].LoadFromDataTable(dt, true);
}
excel.Save();
Of course, I'd recommend some refinements to deal with datatypes, formatting and the like, but this is the basic construct.
Also, of course, use the IDisposable using liberally.

The problem can be divided into two sub problems
Getting Data into c# from postgres.
pushing that data into excel.
Now solving a problem at a time
Here is a good article on working with postgres using c#
once you have you data in c# you can use any one of many libraries available for working with Excel using c#
One of them is NPOI
Here is one with example
Happy Coding.!!!

How to export DataSet values to Excel using EPPlus?

Currently I'm working with ExcelLibrary.dll
The problem with ExcelLibrary is that it makes corrupt excel files if data is less or excel size is less than 6kB.
So I am switching to EPPlus dll.
Currently my code is:
DataSet dsNewDataSet = new DataSet();
string tempTbl = "SELECT * FROM EngineersDetail ORDER BY 3,1";
SqlCommand commandOpen = new SqlCommand(tempTbl, conSql);
SqlDataAdapter adpUpdRow = new SqlDataAdapter();
adpUpdRow.SelectCommand = commandOpen;
adpUpdRow.Fill(dsNewDataSet , "table");
//Create Excel worksheet from the data sets
ExcelLibrary.DataSetHelper.CreateWorkbook("C:/Engineer-wise Performance Report/Engineer-wise Performance Report.xls", dsNewDataSet );
This is a sample code. It selects data from the table EngineersDetail and fill in the DataSet dsNewDataSet, which then dumps data into an excel file.
I later retrieve this excel file generated to send as an attachment in a mail.
Now I want to shift this code completely to EPPlus library code.

Export to excel without using the com object

I'm exporting a dataset to an Excel sheet, but I don't want to use the COM of Excel, because it takes a lot of time.
I need a method that exports to Excel without using the MS Office Interop, and I need to load the method using an empty Excel template so that the new Excel sheet has the same format.

You could reach an excel file and update its contents using ADO.NET and the Jet OleDbProvider
string con = #"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=your_path\test.xls;Extended Properties='Excel 8.0;HDR=No;'";
using(OleDbConnection c = new OleDbConnection(con))
{
c.Open();
string commandString = "Insert into [Sheet1$] (F1, F2, F3) values('F1Text', 'F2Text', 'F3Text')" ;
using(OleDbCommand cmd = new OleDbCommand(commandString))
{
cmd.Connection = c;
cmd.ExecuteNonQuery();
}
}

I use EPPlus. Available via Nuget and LGPL licensed. Let's you create and manage xlsx spreadsheets using OOXML.

I would look into something like this xlslinq
But you can also use this library as it will export it to a dataset

I would suggest using the Open XML SDK 2.0
You will be able to do everything you requested and on top of that it is very fast.

reading data from excel sheet using C#

how to read information inside an excel sheet using C# code......

You can either use Oledb
using System.Data;
using System.Data.OleDb;
OleDbConnection con = new OleDbConnection(#"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Book1.xls;Extended Properties=Excel 8.0");
OleDbDataAdapter da = new OleDbDataAdapter("select * from MyObject", con);
DataTable dt = new DataTable();
da.Fill(dt);
or you use Office Interop
this.openFileDialog1.FileName = "*.xls";
if (this.openFileDialog1.ShowDialog() == DialogResult.OK)
{
Excel.Workbook theWorkbook = ExcelObj.Workbooks.Open(
openFileDialog1.FileName, 0, true, 5,
"", "", true, Excel.XlPlatform.xlWindows, "\t", false, false,
0, true);
Excel.Sheets sheets = theWorkbook.Worksheets;
Excel.Worksheet worksheet = (Excel.Worksheet)sheets.get_Item(1);
for (int i = 1; i <= 10; i++)
{
Excel.Range range = worksheet.get_Range("A"+i.ToString(), "J" + i.ToString());
System.Array myvalues = (System.Array)range.Cells.Value;
string[] strArray = ConvertToStringArray(myvalues);
}
}

Programming with the C API in Excel 2010

If the data is tabular, use OleDB, otherwise you can use Automation to automate Excel and copy the values over to your app.
Or if it's the new XML format excel sheets you might be able to do it via the framework classes.
Info about Excel Automation: How to: Use COM Interop to Create an Excel Spreadsheet
Info about Excel via OleDB: How To Use ADO.NET to Retrieve and Modify Records in an Excel Workbook With Visual Basic .NET

Excel has an API for programming. You can use it to get range of data using c#. You can use something like:
Excel.Application oXL;
Excel._Workbook oWB;
Excel._Worksheet oSheet;
oSheet.get_Range(RangeStart,RangeEnd)

NPOI is the way to go.
Using office interop requires that Office (and the right version) be installed on the machine your app is running on. If a web abb, that probably means no, and it's not robust enough for a production environment anyway. OLEDB has serious limitations, unless it's a one-off and the data is really simple I wouldn't use it.

Excel COM Interop - via Microsoft.Office.Interop.Excel + Microsoft.Office.Interop.Excel.Extensions
ADO.Net via OLEDB data provider for Excel.
Use of System.XML and/or Linq to XML and/or Open XML SDK (can also be used to create new books programmatically from scratch).
3rd party library such as NPOI.
3rd party vendor package such as spreadsheetgear

Loading excel column data using C# in a dropdown menu

I want to load a column in excel into a selectable dropdown menu using c#. I have access to the file, and can load the file in C#, but am not sure how to implement what I want. Suggestions? (I'm using Visual Studio 2008)

You can use the OleDb Managed Data Provider to read an Excel spreadsheet using ADO.NET just like you would with a database.
using System.Data.OleDb;
DataTable dt = new DataTable();
string connString = #"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=c:\Book1.xls;Extended Properties='Excel 8.0;HDR=NO'";
using (OleDbConnection conn = new OleDbConnection(connString))
{
conn.Open();
//Where [F1] = column one, [F2] = column two etc, etc.
OleDbCommand selectCommand = new OleDbCommand("select [F1] AS [id] from [Sheet1$]",conn);
OleDbDataAdapter adapter = new OleDbDataAdapter();
adapter.SelectCommand = selectCommand;
adapter.Fill(dt);
}
listBox1.DataSource = dt;
listBox1.DisplayMember = "id";

You could implement a PIA solution something like this (assuming 5 items in column "A" of the first worksheet):
using Excel = Microsoft.Office.Interop.Excel;
...
worksheet = workbook.Worksheets[1] as Excel.Worksheet;
Excel.Range range;
range = worksheet.get_Range("A1", "A5") as Excel.Range;
foreach (Excel.Range cell in range.Cells)
{
myComboBox.Items.Add(cell.Value2 as string);
}
If you don't know the exact number if items in the dropdown at runtime, you will need to search the range to find the end; check out this sample here.
This sample uses the Office 2007 PIAs, if you are using an older version the syntax should be very close but might vary a bit.

As far as I know you only have a couple of options:
Primary Interop Assemblies (PIA) that let you read and write from the Excel object model.
Building a Visual Studio Tools for Office (VSTO) solution, which effectively lets you write 'code behind' for your Excel spreadsheet. Depending on what you are trying to achieve this can make sense if you are actually doing a lot of work within excel, and your current application is really just creating an extension to the spreadsheet UI.