Using ADO in VBA to connect to PostgreSQL - postgresql

Question

I am having trouble finding clear and reliable examples of connecting to a PostgreSQL database from Excel using VBA ADO. Admittedly, I am new to VBA and most examples and tutorials are very Access or MSSQL centered. (I work mostly in Ruby, Rails, Perl and PostgreSQL.)
I am looking for code to connect and return a simple query (SELECT * FROM customers;) to an Excel sheet. Connection parameters (server ip, user, pass, database) are located within cells in a separate worksheet.
I appreciate your help and patience.
Code:
Sub ConnectDatabaseTest()
Dim cnn As ADODB.connection
Dim cmd As ADODB.Command
Dim param As ADODB.Parameter
Dim xlSheet As Worksheet
Dim rs As ADODB.Recordset
Dim sConnString As String
Dim i As Integer
' Connection Parameters
Dim strUsername As String
Dim strPassword As String
Dim strServerAddress As String
Dim strDatabase As String
' User:
strUsername = Sheets("CONFIG").Range("B4").Value
' Password:
strPassword = Sheets("CONFIG").Range("B5").Value
' Server Address:
strServerAddress = Sheets("CONFIG").Range("B6").Value
' Database
strDatabase = Sheets("CONFIG").Range("B3").Value
Set xlSheet = Sheets("TEST")
xlSheet.Activate
Range("A3").Activate
Selection.CurrentRegion.Select
Selection.ClearContents
Range("A1").Select
Set cnn = New ADODB.connection
sConnString = "DRIVER={PostgreSQL Unicode};DATABASE=" & strDatabase & ";SERVER=" & strServerAddress & _
";UID=" & strUsername & ";PWD=" & strPassword
cnn.Open sConnString
cmd.ActiveConnection = cnn
Dim strSQL As String
strSQL = "SELECT * FROM customers"
cmd.CommandType = ADODB.CommandTypeEnum.adCmdText
cmd.ActiveConnection = cnn
cmd.CommandText = strSQL
...
It seems to break here: cmd.ActiveConnection = cnn
EDIT: added sample code.
EDIT: sConnString gets set to:
DRIVER={PostgreSQL35W};DATABASE=my_database;SERVER=1.2.3.4;UID=analyst;PWD=sekrit
UPDATE 2/7: I changed the 'DRIVER' parameter in the connection string:
sConnString = "DRIVER={PostgreSQL Unicode};DATABASE=" & strDatabase & ";SERVER=" & strServerAddress & _
";UID=" & strUsername & ";PWD=" & strPassword & ";"
...and I get a different error: 'Run-time error 91: Object variable or With block variable not set'
Hm. Ideas?

Answer 1

I wan't using a DSN as I am using an ODBC driver as opposed to OLE DB. By referencing a DSN, the above code works with very few changes.
See this question for how I found the answer once I began to suspect OLE DB/ODBC to the issue.
Does ADO work with ODBC drivers or only OLE DB providers?
New Code here:
Sub GetCustomers()
Dim oConn As New ADODB.connection
Dim cmd As New ADODB.Command
' Connection Parameters
Dim strUsername As String
Dim strPassword As String
Dim strServerAddress As String
Dim strDatabase As String
' User:
strUsername = Sheets("CONFIG").Range("B4").Value
' Password:
strPassword = Sheets("CONFIG").Range("B5").Value
' Server Address:
strServerAddress = Sheets("CONFIG").Range("B6").Value
' Database
strDatabase = Sheets("CONFIG").Range("B3").Value
oConn.Open "DSN=my_system_dsn;" & _
"Database=" & strDatabase & ";" & _
"Uid=" & strUsername & ";" & _
"Pwd=" & strPassword
Set xlSheet = Sheets("CUSTOMERS")
xlSheet.Activate
Range("A3").Activate
Selection.CurrentRegion.Select
Selection.ClearContents
Range("A1").Select
Dim strSQL As String
strSQL = "SELECT * FROM customers"
cmd.CommandType = ADODB.CommandTypeEnum.adCmdText
cmd.ActiveConnection = oConn
cmd.CommandText = strSQL
Set rs = New ADODB.Recordset
Set rs = cmd.Execute
For i = 1 To rs.Fields.Count
ActiveSheet.Cells(3, i).Value = rs.Fields(i - 1).Name
Next i
xlSheet.Range(xlSheet.Cells(3, 1), _
xlSheet.Cells(3, rs.Fields.Count)).Font.Bold = True
ActiveSheet.Range("A4").CopyFromRecordset rs
xlSheet.Select
Range("A3").Select
Selection.CurrentRegion.Select
Selection.Columns.AutoFit
Range("A1").Select
rs.Close
oConn.Close
Set cmd = Nothing
Set param = Nothing
Set rs = Nothing
Set cnn = Nothing
Set xlSheet = Nothing
End Sub
The System DSN is configured to use the PostgreSQL Unicode driver. I chose not to use OLE DB even though there is a provider available. If you look at PGFoundry, you will see it has many problems and has not been updated in several years.

Answer 2

In the original Code, "PostgreSQL35W" is a DSN name which included the default host and port. When you changed to "PostgreSQL Unicode", it is a driver and your connection string is lacking the value for the port. Remember to access PostgreSQL directly from driver, you need at least 5 parameters:
host
port
userid
password
database
If you are using DSN, some parameters may be defined as default.

Answer 3

Not sure about the details of the actual DB connection, but there is a simple although common mistake with your statement: you need to use 'set' when working with objects:
set cmd.ActiveConnection = cnn

Answer 4

Set cmd = New ADODB.Command
cmd.ActiveConnection = cnn