1. CIS 338: Using DAO (Data Access Objects) Dr. Ralph D. Westfall February, 2003

2. Data Access Objects VB objects that can be used in program code to work with databases can set properties in code can use methods " " can do more than with Data control e.g., input validation based on business rules handling data from automated sources

3. Starting a DAO Project start a new VB standard EXE project select Project>References click Microsoft DAO 3.6 Object Library use 2.5/3.5 if will work with older databases

4. Starting a DAO Project - 2 add code that will set up the database above Form_Load code (General): Dim db[Name] As Database in Form_Load code: Dim s[dbloc] As String s[dbloc] = App.Path & "\[file].mdb" 'or use actual physical path Set db[Name] = _ OpenDatabase(s[dbloc])

5. Recordset Type - Table gives direct access to table/all records can change sort order can see changes by other users above Form_Load code: Dim rs[name] As Recordset in Form_Load code: Set rs[name] = _ db[name].OpenRecordset("[table]", _ dbOpenTable) 'sample databasesample database

6. Recordset Type - Dynaset fields/records from one table Set rs[name] = db[name].OpenRecordset_ ("[table]", dbOpenDynaset) can use SQL to get data from multiple tables Dim sSQL as String sSQl = "SELECT … FROM … WHERE …" Set rs[name] = db[name].OpenRecordset_ (sSQL, dbOpenDynaset)

7. Recordset Type - Snapshot gets "read only" copies from one or more tables faster processing uses more memory can't change sort order Set rs[name] = db[name].OpenRecordset_ ("[table]", dbOpenSnapshot) 'table Set rs[name] = db[name].OpenRecordset_ (sSQL, dbOpenSnapshot) 'SQL string

8. Recordset Syntax Set rs[name] = [object].OpenRecordset _ (source, type, options, lockedits) object: usually a database source (required): table, query in database, SQL string optional parameters:  type: must be dbOpenTable for table source, can be dbOpenDynaset, etc. if from query or SQL  options: dbReadOnly, dbForwardOnly, etc.

9. Putting DAO Data in Form add controls (textboxes) to form write code to set property of control to field in database textboxes: set Text property txt[name].Text = _ rs[name].Fields("[name]") 'space prob txt[name].Text = rs[name]![name] could set label Caption similarly 'Notes

10. Using Record Pointer record pointer identifies specific record positioning Move methods – moves pointer Find and Seek methods – goes to specific record Bookmark property – saves location AbsolutePosition – go to record # PercentPosition – go % to of total items

11. Using Record Pointer - 2 Move MoveFirst, MoveNext, MovePrevious, MoveLast Move n e.g. Move 2, Move –35 (negative) rs[name].MoveFirst rs[name].Move 14 'Notes

12. Using Record Pointer - 3 Find FindFirst, FindNext, FindPrevious, FindLast rs[name].FindFirst [criteria] criteria = string like in a SQL WHERE clause sCriteria = "State='CA'" rsCustomers.FindFirst sCriteria rs[name].NoMatch indicates if not found If rsCustomers.NoMatch = True 'not found

13. Using Record Pointer - 4 Bookmark identifies a location (like a record number, but stored as string) sVariable = rs[name].Bookmark stores location of current record rs[name].Bookmark = sVariable moves to bookmarked record rs[name].PercentPosition = 10

14. Conditions in Strings need to get single quotes around strings in an SQL query or Find criteria sCriteria = "[field] = ' " & [string] & " ' "  note ' " before string, " ' after sCriteria = "Title = '" & sTitle & "'"  If sTitle = "Jaws" this evaluates to sCriteria = "Title like 'Jaws'" 'see p. 580

15. Conditions in Strings - 2 can store a single quote as a string variable to set up SQL strings as criteria SQ = "'" 'single quote in double quotes sCriteria = "Title = " & SQ & sTitle & SQ 'also mentioned on p. 580

16. Using Indexes indexes control sort order different indexes for different sorts indexes must be created before recordset can only use indexes with table recordsets, not dynasets or snapshots rs[name].Index = "[name of index]" 'existing index 'creating a new index(MSDN site)creating a new index

17. Filters work with dynasets, snapshots, not tables rs[name].Filter = [criterion] criterion = string like condition in a SQL WHERE clause, but without the word WHERE sCriterion = "Zip='90806'" rsStudents.Filter = sCriterion

18. Sorting works with dynasets and snapshots, but not with tables rs[name].Sort = [field(s)] sorts according to "collating sequence"  in ASCII: spaces first, followed by some quotation marks, numbers, capital letters, more quotation marks, then lower case rsCustomer.Sort = "City, Zip"

19. Updating Database: AddNew adding a record rs[name].AddNew rs[name]![field1] = [value] rs[name]![field2] = [value] rs[name].Update

20. Updating Database: Edit editing a record values replace data in current record rs[name].Edit rs[name]![field1] = [value] rs[name]![field2] = [value] rs[name].Update 'very similar to.Add in DAO

21. Updating Database: Delete deleting a record current record is deleted can use record pointer positioning commands (like Find) to identify record to delete rs[name].Delete before other actions, need to be sure record is not on EOF or will not be on BOF

22. Transaction Processing used when transaction (group of actions) all need to happen to database at same time all or none basis BeginTrans – starts transaction ws[name].BeginTrans 'ws = workspace object RollBack – removes all changes since BeginTrans CommitTrans – permanently saves (can't be rolled back afterwards)