Matakuliah : M0492 / Web-based Programming Lanjut
Tahun
: 2007
Web-based Programming Lanjut
Pertemuan 6
ActiveX Data Object(ADO)
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Cursor
Locking
Creating Recordset
Filtering Recordset
Searching For Records
Modifying Records
Managing Errors
Cursors
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Manages the set of records and the current location within the recordset, the latter being handled by
the current record pointer.
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Cursor types:
– Static (adOpenStatic = 3). Contain a static copy of the records; meaning that the contents
of the recordset are fixed at the time the recordset is created. Any records modified, added, or
deleted by other users will not be visible. Movement through the recordset is allowed both
forwards and backwards.
–
Forward Only (asOpenForwardOnly = 0). The default cursor type, which is identical
to a Static cursor except that you can only move forwards through the recordset.
–
Dynamic (adOpenDynamic = 2). Doesn’t have a fixed set of records. Any changes,
additions or deletions by other users will be visible in the recordset. Movement through the
recordset is allowed both forwards and backwards.
–
Keyset (adOpenKeyset = 1). Similar to Dynamic cursors, except that the set of record is
fixed. You can see changes by other users, but new records are not visible. If other users delete
records, then these will be inaccessible in the recordset. This functionality is achieved by the set
of records being identified by their keys – so the keys remain, even if the records change or are
deleted.
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Cursors
• Cursor Location
– Depends upon the data source.
– Certain data source such as Microsoft SQL Server, have a cursor service of
their own, whereas others, such as Microsoft Access, don’t have a cursor
service.
– When open a recordset, you have to choose whether you want the data store
to manage your cursor, or OLE DB and ADO to manage the cursor locally for
you.
– OLE DB has its own cursor service.
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Cursors
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The two options are decided by using the CursorLocation property of either the
Connection object or the Recordset object.
Set this property to one of two values:
– adUseServer – To let the data store manipulate the cursor
– adUseClient – To let ADO manipulate the cursor
Set this property before open the connection or recordset.
conn.CursorLocation = adUseServer
conn.Open strConn
Or
rsAuthor.CursorLocation = adUseClient
rsAuthor.Open “authors”, conn
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Cursors
• The default cursor is server-based.
• Server cursor – the data store is responsibility to manage the records.
• Client cursor – managed by the local client cursor service and the entire contents
of the recordset are copied onto the client.
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Locking
• Locking is how we ensure the integrity of our data, making sure that changes
aren’t overwritten.
• We need to avoid the classic lost update situation; where one user changes some
data, and then another user changes it immediately afterwards.
• To manage this protection we lock records, just like we lock our house, and there
are several different methods of ensuring that records are protected.
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Locking
• Lock Types
– Read Only (adLockReadOnly = 1). The default locking type, which
means the recordset is read-only, and records cannot be modified.
– Pessimistic (adLockPessimistic = 2). When amending a record, the
provider will try to lock the record to guarantee the successful editing of the
record. This is generally accomplished by locking the record as soon as editing
takes place.
– Optimistic (adLockOptimistic = 3). The record is not locked until
the changes to the record are committed to the data store, by way of the
Update method.
– Batch Optimistic (adLockBatchOptimistic = 4). Batch
optimistic locking allows multiple records to be modified, and the records are
only locked when the UpdateBatch method is called.
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Locking
• When you don’t need to modify any records, use a Read-Only recordset.
• For general use, Optimistic is probably best, since the data store only locks the
record for a small period of time – whilst it’s actually updating the data. This
reduces the resources used.
• Pessimistic locking increases data integrity, but at the cost of concurrency. This
is the ability of many users to view the data at once. A locked record is not
available for viewing by other users, therefore concurrency is reduced.
• Optimistic locking locks the record for a shorter period of time and therefore
increases concurrency, but there’s a greater chance of the data being modified by
others.
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Creating Recordsets
• Creating a recordset is achieve by the open method of the Recordset object
Recordset.Open [Source], [ActiveConnection], [LockType], [Options]
Argument
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Description
Source
The source of the data. This can be the name of the table from a database, a stored query
or procedure, a SQL string, a Command object, or any other command applicable to the
Provider.
ActiveConnection
The connection to use for the recordset. This can be a connection string or an open
Connection object.
CursorType
The type of cursor to use. This must be one of the defined cursor types. The default is
adForwardOnly.
LockType
The type of locking to use. This must be one of the defined lock types. The default is
adLockReadOnly.
Options
Tells the provider what the Source argument is – that is, whether it is a table, a text string,
and so on.
Creating Recordsets
For example, to open a recordset on the authors table in the pubs database:
Dim rsAuthors
Set rsAuthors = Server.CreateObject(“ADODB.Recordset”)
rsAuthors.Open “authors”, strConn
‘ Do something here
rsAuthor.Close
Setrsauthors = Nothing
Notice that several of the arguments have been left off. In fact, all of the argument are
optional, and you could set their corresponding properties before opening the recordset:
Dim rsAuthors
Set rsAuthors = Server.CreateObject(“ADODB.Recordset”)
With rsAuthors
.Source = “author”
.ActiveConnection = strConn
.CurcorType = adOpenForwardOnly
.LockType = adLockReadOnly
.Open
End With
‘ Do something here
rsAuthor.Close
Setrsauthors = Nothing
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Creating Recordsets
Once the recordset has been opened, you are automatically placed on the first
record. If there are no records in the recordset, then both BOF and EOF properties
will be True
rsAuthors.Open “authors”, strConn
If rsAuthors.BOF and rsAuthors.EOF Then
‘ Recordset is empty
End If
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Creating Recordsets
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The Option Argument
Allows to specify what the command text contains.
It can be one of the following CommandTypeEnum constants:
– adCmdText (1)– To Indicate a text command, such as a SQL String
– adCmdTable (2) – To indicate the name of a table
– adCmdStoredProc (4) – To indicate the name of a stored procedure
– adCmdFile (256)– To Indicate the file name of a saved recordset
– adCmdTableDirect (512)– To indicate the name of a table
– adCmdURLBind – To indicate a URL
The difference between adCmdTable and adCmdTableDirect is small, but if
you want all columns from a table, then adCmdTableDirect is marginally faster, as ADO
performs some internal optimization.
There are also 2 other options: adCmdUnspecified (-1), indicating that no type is specified,
and adCmdUnknown (8), indicating that the command type is unknown. In general you
won’t probably use this.
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Creating Recordsets
Additional Options
The option argument can be one of the previous constants, but you can also add in one of
the following ExecuteOptionEnum constants:
– adAsyncExecute (16)– To indicate the command should be executed
asynchronously
– adAsyncFetch (32)– To indicate that after the initial set of rows has been
fetched, and remaining rows are fetched asynchronously
– adAsyncFetchNonBlocking (64)– Similar to adAsyncFetch, except that the
fetching of records never blocks commands
– adExecuteNoRecords (128)– To indicate that the command does not return any
records
Asynchronous processing means that the actions happen in the background; so instead of
running a command and waiting for it to finish (synchronously), you can run the
command, and then carry on doing something else, whilst the command is executing in
the background.
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Creating Recordsets
• The adExecuteNoRecords option is extremely useful. It tells ADO that the
command you are executing does not return any data; therefore, there is no point
in building a recordset. This can be speed up action queries.
• To add one of this options you can use the Or statement (Or = +)
adCmdStoredProc Or adExecuteNoRecords
adCmdStoredProc + adExecuteNoRecords
• Moving Through the Recordset
– MoveFirst
– MoveNext
– MoveLast
– MovePrevious
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Filtering Recordsets
• Filtering is a way of temporarily restricting the view of records in a recordset.
• Filtering with a Criteria
The Filter property takes a variety of arguments, one of which is a criterion
very much like a SQL WHERE clause:
rsAuthors.Filter = “state = ‘ca’ ”
rsAuthors.Filter = “au_lname = ‘Homer’ or au_lname = ‘Francis’ ”
rsAuthors.Filter = “au_lname LIKE ‘Ho%’ ”
Use the empty string to reset (clean) the filter, so that all records are once
again shown:
rsAuthors.Filter = “”
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Filtering Recordsets
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Filtering with a Constant
– adFilterNone (0)– To remove the current filter. This has the same effect as using
an empty string.
– adFilterPendingRecords (1)– To view only records that have changed, but
have not yet been sent to the server. This only applicable in batch update mode.
– adFilterAffectedRecords (2)– To view only records affected by the last
Delete, Resync, UpdateBatch or CancelBatch method call.
– adFilterFetchedRecords (3)– To view records in the cache. This means the
results of the last method call to retrieve records.
– adFilterConflictingRecords (5)– To view records that failed to update during
the last batch update.
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Filtering Recordsets
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Filtering with Bookmarks
The last method of filtering recordsets is to use an array of bookmarks. This allow you to
build up a list of records, and then at a later date apply a filter.
rsAuthors.Open “authors”, strConn, adOpenKeyset, adLockReadOnly, adCmdTableDirect
avarBkmk(0) = rsAuthors.Bookmark
‘Save bookmark for the first record
rsAuthors.MoveNext
rsAuthors.MoveNext
‘Move forward two records
avarBkmk(1) = rsAuthors.Bookmark
‘Save Bookmark for the third record
rsAuthors.MoveLast
avarBkmk(2) = rsAuthors.Bookmark
‘Move to the end and save the bookmark
rsAuthors.Filter = Array (avarBkmk(0), avarBkmk(1), avarBkmk(2)) ‘Now apply the filter
While Nor rsAuthors.EOF
Response.Write rsAuthors (“au_lname”) & “<BR>”
rsAuthors.MoveNext
Wend
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‘Now loop through the recordset
Searching For Records
• Searching for individual is performed with the “Find” method.
rsAuthors.Find “au_lname=‘Lloyd’”
• Also can use optional arguments to specify some extra option.
Recordset.Find Criteria, [SkipRows], [SearchDirection], [Start]
• If the record isn’t found, then the position is in one of two places :
•SkipRows indicating the number of rows to skip before starting the search
(default 0).
•SearchDirection can be either adSearchForward or adSearchBackward
•Start identifying the position from which to start the search.
•If Searching forwards, position is after the end of the recordset, and EOF is set
•If Searching backwards, position is before the start of the recordset, and BOF is set
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Searching For Records
• Using Bookmarks to Save the Position
This re-positioning when records are not found is one place where bookmarks
come in handy, since the current position bookmarked, search for a record, and if
not found, move back to the saved position.
‘Save the bookmark position
varBkmk = rsAuthors.Bookmark
‘Find the record
rsAuthors.Find “au_lname = ‘Sussman’”
‘Was it found
If Not rsAuthors.EOF Then
Response.Write “Found: “ & rsAuthors(“au_lname”) & “, “ & rsAuthors(“au_fname”) & “ <BR>
Else
Response.Write “Not found. Moving <BR>”
rsAuthors.Bookmark = varBkmk
End If
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Modifying Records
• Using the Recordset object’s methods, can use a locking type other than
adLockReadOnly to be able to change the data.
• The default locking type is read-only
• Modifying can be :
– Adding Records
– Editing Records
– Deleting Records
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Modifying Records
• Adding Records
– There are two ways of using this.
– The first (simply adds a new record, setting the four mandatory fields)
With rsAuthors
.Open “authors”, strConn, adOpenDynamic, adLockOptimistic, adCmdTableDirect
.AddNew
.Fields(“au_id”) = “123-12-1234”
.Fields(“au_lname”) = “Lloyd”
.Fields(“au_fname”) = “Janine”
.Fields(“contract”) = 0
.Update
End With
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Modifying Records
– An alternative way is to use the optional arguments of the AddNew method,
which are two arrays – one of the field names and one of the fields values :
With rsAuthors
.Open “authors”, strConn, adOpenDynamic, adLockOptimistic, adCmdTableDirect
.AddNew Array (“au_id”, “au_lname”, “au_fname”, “contract”), _
Array (“123-12-1234”, “Lloyd”, “Janine”, 0)
End With
– This method doesn’t require a call to the Update method.
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Modifying Records
• Editing Records
Similar to the first method of inserting records – the difference being that you
don’t need to call the AddNew method
strSQL = “SELECT * FROM authors WHERE au_lname=‘Lloyd’”
With rsAuthors
.Open strSQL strConn, adOpenDynamic, adLockOptimistic, adCmdText
.Fields(“contract”) = 1
.Update
End With
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Modifying Records
• Deleting Records
– To delete records, call the Delete method.
– The optional argument, can be one of the AffectEnum constants
• adAffectCurrent (1)– to indicate only the current record is deleted.
This is the default action.
• adAffectGroup (2)– to indicate that all records matching the current
filter are deleted.
• adAffectAll (3)– to indicate all records in the recordset are deleted.
• adAffectAllChapters (4)– to indicate that records in all chapters
are deleted.
rsAuthors.Delete
rsAuthors.Delete adAffectGroup
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Managing Errors
• The Errors Collection
– Contains an Error Object for each error that occurred during a single ADO
command.
– Multiple errors may be occur during a command, and the OLE DB provider
needs a way to inform the client that more than one error has occurred.
– Two important points:
• Each time ADO command is run, if an error occurs, the Errors collection is
cleared and filled with the new details. However, if no error occurred, the
Errors collection is not touch. Therefore the collection may contain errors
even though the ADO command completed successfully.
• The OLE DB Provider may fill the Errors collection with informational
messages or warnings, which will have an error number of 0. Therefore
you cannot just check the number of errors in the collection and assume
that an error has occurred.
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Managing Errors
• The Errors collection is only accessible from the Connection object.
• If you haven’t explicitly created a Connection object, the Recordset object has an
ActiveConnection property, which contains the Connection object for the current
Recordset. You can get the Errors collection like so:
rsAuthors.ActiveConnection.Errors
To see all errors that occur, loop through the collection:
For Each errAuthorss In rsAuthors.ActiveConnection.Errors
‘ Display error
Next
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Managing Errors
• Properties of the Error object
Property
Description
Number
The ADO error number
NativeError
The error number from the data provider
SQLState
The 5 digit SQL state code for the error, when connecting to SQL databases
Source
The object that generated the error
Description
Descriptive text of the error
For Each errAuthorss In rsAuthors.ActiveConnection.Errors
Response.Write “Number: “ & errAuthors.Number & _
“<BR>NativeError: “ & errAuthors.NativeError & _
“<BR>SQL State: “ & errAuthors.SQLState & _
“<BR>Source: “ & errAuthors.Source & _
“<BR>Description: “ & errAuthors.Description& _
“<P>”
Next
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<HTML>
<HEAD>
<TITLE>ADO Errors in ASP Page</TITLE>
</HEAD>
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<BODY>
<!-- #include file="dataconn.inc" -->
<%
On Error Resume Next ‘ The best way to check for errors
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strSQL = "SELECT missColumn1,missColumn2, au_lname, au_fname FROM authors"
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set rsAuthors = Server.CreateObject("ADODB.REcordset")
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rsAuthors.Open strSQL, conn
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If CheckForErrors(rsAuthors.ActiveConnection) = False then
While Not rsAuthors.EOF
Response.Write rsAuthors("au_lname") & ", " & rsAuthors("au_fname") & "<BR>"
rsAuthors.MoveNext
Wend
End if
rsAuthors.Close
Set rsAuthors = Nothing
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%>
</BODY>
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<SCRIPT LANGUAGE="VBScript" RUNAT="SERVER">
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Function CheckForErrors(objConn)
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Dim objError
'Error Object
If objConn.Errors.Count >0 Then
‘Errors means the count will be greater than 0
For Each objError in objConn.errors
If objError.Number<>0 Then
'Errors with number 0 are informational
Response.Write "<P><TABLE BORDER=1>" & _
"<TR><TD>Error Property</TD><TD>Contents</TD></TR>" & _
"<TR><TD>Number</TD><TD>" & objError.Number & "</TD></TR>" & _
"<TR><TD>NativeError</TD><TD>" & objError.NativeError & "</TD></TR>" & _
"<TR><TD>SQLState</TD><TD>" & objError.SQLState & "</TD></TR>" & _
"<TR><TD>Source</TD><TD>" & objError.Source & "</TD></TR>" & _
"<TR><TD>Description</TD><TD>" & objError.Description & "</TD></TR></TABLE>"
CheckForErrors = True
End If
Next
Else
CheckForErrors = False
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End If
End Function
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</SCRIPT>
</HTML>
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ADO Errors in ASP Page
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