Designing a VBA Library for Data Integration

Follow this structured strategy to create a VBA library for handling data from multiple sources like Excel, SQL Server, and Tableau.

1. Plan Your Library Architecture

Organize your .bas files into logical modules for maintainability and reusability:

• DataConnection.bas: Handles connections to data sources.
• DataRetrieval.bas: Functions for fetching data from SQL Server and reading data from spreadsheets.
• DataTransformation.bas: Utilities for data cleaning and transformation.
• Utilities.bas: General-purpose utilities like logging and error handling.

2. Establish Standards and Best Practices

• Use descriptive function names for clarity.
• Document each function with comments explaining its purpose, inputs, and outputs.
• Implement error handling in every function to manage runtime issues gracefully.
• Store sensitive data securely and use constants for configurations.

3. Create a DataConnection.bas Module

Option Explicit

' Connection strings
Public Const SQL_CONNECTION_STRING As String = "Your SQL Server connection string"

' Function to connect to SQL Server
Public Function GetSQLConnection() As Object
    Dim conn As Object
    Set conn = CreateObject("ADODB.Connection")
    conn.ConnectionString = SQL_CONNECTION_STRING
    conn.Open
    Set GetSQLConnection = conn
End Function

4. Develop a DataRetrieval.bas Module

This module handles pulling data from SQL Server tables and reading data from existing spreadsheets.

Option Explicit

' Function to retrieve data from SQL Server and write it to a table in the current workbook
Public Sub FetchDataToTable(sqlQuery As String, targetSheetName As String)
    Dim conn As Object, rs As Object, targetSheet As Worksheet, rowNum As Long, colNum As Long
    Set conn = GetSQLConnection()
    Set rs = CreateObject("ADODB.Recordset")
    rs.Open sqlQuery, conn

    Set targetSheet = ThisWorkbook.Sheets(targetSheetName)
    targetSheet.Cells.Clear

    ' Write headers
    For colNum = 1 To rs.Fields.Count
        targetSheet.Cells(1, colNum).Value = rs.Fields(colNum - 1).Name
    Next colNum

    ' Write data
    rowNum = 2
    Do Until rs.EOF
        For colNum = 1 To rs.Fields.Count
            targetSheet.Cells(rowNum, colNum).Value = rs.Fields(colNum - 1).Value
        Next colNum
        rowNum = rowNum + 1
        rs.MoveNext
    Loop

    rs.Close
    conn.Close
End Sub

' Function to read data from a specific tab in an Excel workbook on the network and write it to a tab in the current workbook
Public Sub ReadNetworkTabToSheet(filePath As String, sourceSheetName As String, targetSheetName As String)
    Dim xlApp As Object, xlBook As Object, xlSheet As Object, targetSheet As Worksheet, data As Variant
    Set xlApp = CreateObject("Excel.Application")
    Set xlBook = xlApp.Workbooks.Open(filePath)
    Set xlSheet = xlBook.Sheets(sourceSheetName)

    data = xlSheet.UsedRange.Value

    Set targetSheet = ThisWorkbook.Sheets(targetSheetName)
    targetSheet.Cells.Clear
    targetSheet.Cells(1, 1).Resize(UBound(data, 1), UBound(data, 2)).Value = data

    xlBook.Close False
    xlApp.Quit
End Sub

' Function to create INSERT statements from a table in a sheet and write them to a specified sheet
Public Sub CreateInsertStatements(tableName As String, sourceSheetName As String, targetSheetName As String)
    Dim sourceSheet As Worksheet, targetSheet As Worksheet, rowNum As Long, colNum As Long, lastRow As Long, lastCol As Long
    Dim header As Variant, dataRow As Variant, insertStatement As String

    ' Set source and target sheets
    Set sourceSheet = ThisWorkbook.Sheets(sourceSheetName)
    On Error Resume Next
    Set targetSheet = ThisWorkbook.Sheets(targetSheetName)
    If targetSheet Is Nothing Then
        Set targetSheet = ThisWorkbook.Sheets.Add
        targetSheet.Name = targetSheetName
    End If
    On Error GoTo 0
    targetSheet.Cells.Clear

    ' Get headers and data
    lastRow = sourceSheet.Cells(sourceSheet.Rows.Count, 1).End(xlUp).Row
    lastCol = sourceSheet.Cells(1, sourceSheet.Columns.Count).End(xlToLeft).Column
    header = sourceSheet.Cells(1, 1).Resize(1, lastCol).Value

    ' Write INSERT statements
    rowNum = 1
    For rowNum = 2 To lastRow
        dataRow = sourceSheet.Cells(rowNum, 1).Resize(1, lastCol).Value
        insertStatement = "INSERT INTO " & tableName & " ("
        For colNum = 1 To lastCol
            insertStatement = insertStatement & header(1, colNum) & ", "
        Next colNum
        insertStatement = Left(insertStatement, Len(insertStatement) - 2) & ") VALUES ("
        For colNum = 1 To lastCol
            insertStatement = insertStatement & "'" & Replace(dataRow(1, colNum), "'", "''") & "', "
        Next colNum
        insertStatement = Left(insertStatement, Len(insertStatement) - 2) & ");"
        targetSheet.Cells(rowNum - 1, 1).Value = insertStatement
    Next rowNum
End Sub

5. Build a DataTransformation.bas Module

Option Explicit

' Function to clean data
Public Function CleanData(data As Variant) As Variant
    Dim i As Long
    For i = LBound(data) To UBound(data)
        data(i) = UCase(Trim(data(i)))
    Next i
    CleanData = data
End Function

' Function to format billing data
Public Function FormatBillingData(data As Object) As Object
    ' Apply transformations to the recordset
    Set FormatBillingData = data
End Function

6. Implement Utilities in Utilities.bas

Option Explicit

' Logging function
Public Sub LogMessage(message As String)
    Dim logFile As String
    logFile = ThisWorkbook.Path & "\Log.txt"
    Open logFile For Append As #1
    Print #1, Now & ": " & message
    Close #1
End Sub

' Error handling utility
Public Function HandleError(err As Object) As String
    LogMessage "Error " & err.Number & ": " & err.Description
    HandleError = "Error occurred: " & err.Description
End Function

7. Establish a Development Workflow

• Test each module independently.
• Integrate step-by-step, starting with basic queries and file reads.
• Use version control tools like Git to track changes in your .bas files.
• Maintain central documentation for your library.

8. Example Workflow for Using the Library

' Fetch data from SQL Server table to a sheet
Call FetchDataToTable("SELECT * FROM BillingData", "TargetSheet")

' Read data from an Excel sheet on the network to a sheet
Call ReadNetworkTabToSheet("\\network_path\file.xlsx", "SourceSheet", "TargetSheet")

' Create INSERT statements from a table and write them to a sheet
Call CreateInsertStatements("TargetTable", "SourceSheet", "InsertStatementsSheet")

' Log activities
LogMessage "Data successfully retrieved and processed."

This strategy ensures your VBA library is modular, maintainable, and scalable for integrating data from various sources into your billing processes.