DOCERR: More Info & Doc Fixes for FindFirst & Seek Methods

• Professional Edition of Microsoft Visual Basic for Windows, version 3.0

SUMMARY

The status of database objects after a search operation (FindFirst or Seek) is not clearly documented. Data Controls, Dynasets, and Snapshots all maintain a valid record while Table objects actually have "No Current Record" after an unsuccessful Seek (NoMatch = true).

In addition, there are two documentation errors:

• The "Language Reference" manual gives incorrect information regarding the FindFirst, FindLast, FindNext, and FindPrevious methods in the second paragraph on Page 200:

       If no matching records are found, the NoMatch property is TRUE and the
       current record remains the same as before the Find method was used.
  

• The "Language Reference" manual gives incorrect information regarding the Seek method in the first paragraph on Page 504:

        NOTE: Always inspect the value of the NoMatch property of the
        recordset to determine whether the SEEK method has succeeded. If it
        fails, NoMatch is TRUE and the current record is unchanged"
  

MORE INFORMATION

FindFirst - Data Controls and Dynasets

By in large these objects behave as would be expected. When the Find method fails to find a match the NoMatch property of the RecordSet is set to TRUE. However, the current record does change. It is set to the first record in the recordset.

Seek - Table Objects

When the Seek method fails to find a match, the NoMatch property of the RecordSet is set to TRUE, as it is with the Find method. However, the current record also changes. In fact it becomes invalid, so that it returns the error message, "No Current Record" if you attempt to access it.

Steps to Reproduce Behavior

1. Start a new project in Visual Basic. Form1 is created by default.

2. Add three command buttons (Command1, Command2, and Command3) to the lower-right corner of Form1 and change their Caption properties to: Create DB, Seek, and Find.

3. Add the following code to the Command1_Click event procedure:

      Sub Command1_Click ()
         Const DB_LANG_GENERAL = ";LANGID=0x0809;CP=1252;COUNTRY=0"
         Const DB_DOUBLE = 7
         Const DB_TEXT = 10
   
         Dim db As Database
         Dim tb As table
         Set db = CreateDatabase(App.Path + "\NUMBERS.MDB", DB_LANG_GENERAL)
   
         Dim td As New tabledef
         Dim F1 As New field
         Dim F2 As New field
   
         td.Name = "Amounts"
   
         F1.Name = "Desc"
         F1.Type = DB_TEXT
         F1.Size = 35
         td.Fields.Append F1
   
         F2.Name = "Num1"
         F2.Type = DB_DOUBLE
         td.Fields.Append F2
   
         db.TableDefs.Append td
   
         Dim TempIndex As New Index
         TempIndex.Name = "test"
         TempIndex.Fields = "num1"
         db.TableDefs("Amounts").Indexes.Append TempIndex
   
         Set tb = db.OpenTable("Amounts")
   
         For I = 0 To 10
            tb.AddNew
            tb.Fields("Desc") = "hello" & I
            tb.Fields("Num1") = CDbl(I * 10)
            tb.Update
         Next I
   
         tb.Close
         db.Close
      End Sub
   
   

4. Add the following code to the Command2_Click event procedure:

      Sub Command2_Click ()
         On Error GoTo eh
         Dim db As Database
         Dim tb As table
   
         Set db = OpenDatabase(App.Path + "\NUMBERS.MDB")
         Set tb = db.OpenTable("Amounts")
   
         Print "====Test of Seek Method===="
         tb.Index = "test"
         tb.MoveFirst
         Print "MoveFirst  Values= "; tb(0); tb(1)
         tb.Seek "=", 50      ' Finds valid record.
         Print "Seek = 50   NoMatch="; tb.NoMatch; " Values= "; tb(0); tb(1)
         Print
   
         tb.MoveNext
         Print "MoveNext   Values= "; tb(0); tb(1)
         tb.Seek "=", 500     ' Doesn't find valid record.
         Print "Seek = 500  NoMatch="; tb.NoMatch; " Values= "; tb(0); tb(1)
   
         tb.Close
         db.Close
         Exit Sub
   
         eh:
            Print
            Print "*** Error Occurred displaying Current Record ***"
            Print
            Resume Next
      End Sub
   
   

5. Add the following code to the Command3_Click event procedure:

      Sub Command3_Click ()
         Dim db As Database
         Dim ds As Dynaset    ' OR Dim ds As snapshot
   
         Set db = OpenDatabase(App.Path + "\NUMBERS.MDB")
         Set ds = db.CreateDynaset("Amounts")
         ' OR Set ds =    db.CreateSnapshot("Amounts")
   
         Print "====Test of FindFirst Method===="
         ds.MoveFirst
         Print "MoveFirst      Values= "; ds(0); ds("Num1")
         ds.FindFirst "num1 = 50"
   
         ' Enter the following two lines as one, single line:
         Print "FindFirst 50   NoMatch="; ds.NoMatch; " Values= ";
          ds(0); ds("Num1")
         Print
   
         ds.MoveNext
         Print "MoveNext       Values= "; ds(0); ds("Num1")
         ds.FindFirst "num1 = 500"
   
         ' Enter the following two lines as one, single line:
         Print "FindFirst 500  NoMatch="; ds.NoMatch; " Values= ";
          ds(0); ds("Num1")
         Print
   
         ds.Close
         db.Close
      End Sub
   
   

6. Press the F5 key to run the program. Click the Command1 button to create the NUMBER.MDB database. Then click the Command2 button to perform a Seek on the NUMBERS.MDB database, and click the Command3 button to perform a FindFirst on the NUMBERS.MDB database. Review the results that are printed on Form1.