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IN THE SPOTLIGHT: Code Protector
Standard compilation to MDE/ACCDE format is flawed and reversible.
Provided by Allen Browne, November 2003. Updated April 2010.
The DLookup() function in Access retrieves a value from a table. For basic information on how to use DLookup(), see Getting a value from a table.
DLookup() has several shortcomings:
ELookup() addresses those limitations:
Limitations of ELookup():
You can resolve the last issue by concatenating the value into the string:
ELookup("Surname", "Clients", "ClientID = " & [Forms].[Form1].[ClientID])
Before using ELookup() in a query, you may want to modify it so it does not pop up a MsgBox for every row if you get the syntax wrong. Alternatively, if you don't mind a read-only result, a subquery would give you faster results than any function.
The function accepts exactly the same arguments as DLookup(), with an optional fourth argument. It builds a query string:
SELECT Expr FROM Domain WHERE Criteria ORDER BY OrderClause
This string opens a recordset. If the value returned is an object, the requested expression is a multi-value field, so we loop through the multiple values to return a delimited list. Otherwise it returns the first value found, or Null if there are no matches.
Note that ELookup() requires a reference to the DAO library. For information on setting a reference, see References.
Public Function ELookup(Expr As String, Domain As String, Optional Criteria As Variant, _ Optional OrderClause As Variant) As Variant On Error GoTo Err_ELookup 'Purpose: Faster and more flexible replacement for DLookup() 'Arguments: Same as DLookup, with additional Order By option. 'Return: Value of the Expr if found, else Null. ' Delimited list for multi-value field. 'Author: Allen Browne. allenbrowne.com 'Updated: December 2006, to handle multi-value fields (Access 2007 and later.) 'Examples: ' 1. To find the last value, include DESC in the OrderClause, e.g.: ' ELookup("[Surname] & [FirstName]", "tblClient", , "ClientID DESC") ' 2. To find the lowest non-null value of a field, use the Criteria, e.g.: ' ELookup("ClientID", "tblClient", "Surname Is Not Null" , "Surname") 'Note: Requires a reference to the DAO library. Dim db As DAO.Database 'This database. Dim rs As DAO.Recordset 'To retrieve the value to find. Dim rsMVF As DAO.Recordset 'Child recordset to use for multi-value fields. Dim varResult As Variant 'Return value for function. Dim strSql As String 'SQL statement. Dim strOut As String 'Output string to build up (multi-value field.) Dim lngLen As Long 'Length of string. Const strcSep = "," 'Separator between items in multi-value list. 'Initialize to null. varResult = Null 'Build the SQL string. strSql = "SELECT TOP 1 " & Expr & " FROM " & Domain If Not IsMissing(Criteria) Then strSql = strSql & " WHERE " & Criteria End If If Not IsMissing(OrderClause) Then strSql = strSql & " ORDER BY " & OrderClause End If strSql = strSql & ";" 'Lookup the value. Set db = DBEngine(0)(0) Set rs = db.OpenRecordset(strSql, dbOpenForwardOnly) If rs.RecordCount > 0 Then 'Will be an object if multi-value field. If VarType(rs(0)) = vbObject Then Set rsMVF = rs(0).Value Do While Not rsMVF.EOF If rs(0).Type = 101 Then 'dbAttachment strOut = strOut & rsMVF!FileName & strcSep Else strOut = strOut & rsMVF![Value].Value & strcSep End If rsMVF.MoveNext Loop 'Remove trailing separator. lngLen = Len(strOut) - Len(strcSep) If lngLen > 0& Then varResult = Left(strOut, lngLen) End If Set rsMVF = Nothing Else 'Not a multi-value field: just return the value. varResult = rs(0) End If End If rs.Close 'Assign the return value. ELookup = varResult Exit_ELookup: Set rs = Nothing Set db = Nothing Exit Function Err_ELookup: MsgBox Err.Description, vbExclamation, "ELookup Error " & Err.number Resume Exit_ELookup End Function
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