cis 338: using ado (activex data objects) [largely replaced by adonet.vb] dr. ralph d. westfall...

CIS 338: Using ADO (ActiveX Data Objects)

[largely replaced by adonet.vb]

Dr. Ralph D. WestfallApril, 2003

Universal Data Access

ADO.NET is part of Microsoft's universal data access strategy Universal Data Access FAQs

ODBC: open database connectivity API standard for using relational

databases API = application programming interface includes "drivers" for Access, dBase,

DB2, Excel, text, etc. Microsoft is leading ODBC backer

Universal Data Access - 2

OLEDB: DB object linking & embedding next step beyond ODBC accesses relational databases with ODBC provides access to other data also

e-mail, video, voice, images, web pages, etc., etc.

data is accessed "in place" (no need to first move it into a database)

OLEDB Concepts

data store = "persistent" collection of datadata provider = gets data from data store OLEDB "driver": database, email data, etc. OLEDB "has nothing to do with Object

Linking and Embedding" (Word, Excel)

data consumer = application that uses data ADO (ActiveX Data Object) interfaces to data

store through OLEDB

ADO.NET

replaceS DAO, RDO and previous ADOcan use ADO.NET with VB in code via object interface

more powerful than DAO and previous ADO

numerous objects with useful properties and methods

OLEDB with ADO.NET

dataset object copy of data in memory, rather than

connected to the database can have 1 to many DataTable objects

ADO.NET OLEDB data providers SQLClient driver for SQL Server (Microsoft) OleDBClient driver for other databases

DataSet Object Data Tables

"collections" of table(s) information rows, columns of table relationships with other tables constraints to manage

additions/deletions from tables that are related to other tables

data "views" that allow data to be seen in different ways than it is stored in table(s)

Data Provider Objects

connection (to file or server)command object runs SQL or stored procedures in the databasedata reader (if need high performance) read only, forward only

data adaptor (more capabilities) add, change, delete, relate tables

ADO.NET: XML Data Transfer

industry standard for transferring data like HTML, but can create other tags HTML: <title>[some text]</title> XML: <price>[value for price]</price>

like HTML, can have tags within others HTML: <html><body></body></html> XML: <name><first></first></name>

XML Schema

separate file that describes data in an XML file type of data: numeric, text, etc. occurrences: 0 or 1, or either to many relationships e.g., name includes 1st

and last names other characteristics e.g., primary key

Exercise

create your own tags for something you are familiar with food, pets, motor vehicles, video

games, ways to communicate, college courses, etc.

make sure that tags are "nested" open and close inside other "boxes"

then fill in with some sample data

Database System Options

SQL Server high performance not well-suited for using on one

computer

Microsoft Data Engine (MSDE) chopped down version of SQL Server can work with SQL Server files but also can work with Microsoft Access

Creating an MSDE Database

note: may have problems on networkstart AccessFile>New, New>Project (New Data)Access creates a MSDE database (.adp) data storage is different, but you can work

with it like an Access database (.mdb) can edit data or upload files as with .mdb

Connecting ADO to Access

start a new .NET Windows applicationView>Server Explorerright click Data Connections>Add Connectionclick Provider tab>Microsoft Jet 4.0 OLE DB Provider>Next buttonbrowse … for Access database>OK

Using Data Connection

viewing data in a tablein Server Explorer, expand Data Connections, Access, Tables iconsright click on a Table>Retrieve Data from Tableclose this preview window

Create a DataAdapter

in Server Explorer, click and drag a Table onto the form note 2 new components in tray below

right click DataAdaptor>Generate Dataset

DataGrid with DataAdapter

add a DataGrid set DataSource property to DataSetin Form_Load, use .Fill method of DataAdapter with DataSet as argument Click Start to view DataGrid

List/ComboBox with DataSet

drag/drop ListBox onto formset DataSource to DataSet (drop down)set DisplayMember to a field in tableadd .Fill method of DataAdapter see previous slide if didn't do this already

note that data is in same order as in database (not sorted)

DataView List/ComboBox

DataView makes it possible to sort and do other things with database datadrag/drop DataView object to form/trayset DataView Table property to a table from the DataSet (drop down)type in a field name for Sort property see field names in Server Explorer

DataView List/ComboBox - 2

drag/drop ComboBox onto formset DataSource to DataSet (drop down)set DisplayMember to a field in tableadd .Fill method of DataAdapter see previous slide if didn't do this already

can set .ListIndex property to -1 so that no item is selected at start (ListBox too)

SQL as Source of Data

expand DataAdaptor Select Command property to see CommandText codecan modify this SQL by changing the line, or by clicking … to see Query Builder can (un)select fields in Output column can add a WHERE condition value ? in the Criteria column(s) prompts user

Binding Other Controls to Data

draw TextBox or Label on formexpand (DataBindings) propertyclick Text, and select table/field from drop downadd code to load DataSet with just the item input or selected in another control

Binding Other Controls - Code

Setting Up ADO with a DSN

Windows (not VB): Start>Settings>Control Panel[>Administrative Tools>Data Sources] click Data Sources (32 bit) [User DSN tab] select MS Access Database, click Add select Microsoft Access Driver, click Finish click select, choose database (e.g., BIBLIO) type in Data Source Name (DSN) and

description, then click OK put in what you want to call DSN, your

description

Using ADO Data Control

right click toolbox, select Componentsclick Microsoft ADO Data Control 6.0, OKclick Adodc control on toolbar, draw on formright click on control to see Properties page first set up Source of Connection (General

tab) select Use ODBC Data Source Name and

select the DSN you just created (or Use Connection String>Build etc. with latest Microsoft Jet [=Access] Provider)

Using ADO Data Control - 2

select RecordSource tabselect 1 of following Command Types: adCmdText – need to type in SQL query adCmdTable – need to select the table

name adCmdStoredProcedure – need to select

the procedure nameenter SQL, or select Table or stored procedure (e.g., Publishers), click OK

Using ADO Data Control - 3

add controls (e.g., 2 textboxes) to formbind controls to data fields (like with DAO; e.g., Name, City) set DataSource properties = name of

data control from dropdown list set DataField properties to field names

from dropdown list run project, scroll with ADO data control

Using Code & ADODC Control

'command button event code (need a 3rd

'textbox to run this)Dim sState as String, sSQL as StringsState = Text3.Text '3rd TextBoxsSQL = "select * from Publishers"If sState <> "" Then sSQL = sSQL & _" WHERE State = '" & sState & "'" 'spaceAdodc1.CommandType = adCmdTextAdodc1.RecordSource = sSQLAdodc1.Refresh

Data Grid Control

displays database data on a form like in a spreadsheetcan use this layout to edit data in the database

Using DataGrid Control

right click toolbox, select Components click Microsoft ADO Data Control 6.0 click Microsoft Data Grid Control 6.0, OK

click Adodc control on toolbar, draw on formright click on Adodc control to see Properties 1st set Source of Connection (General tab) select Use ODBC Data Source Name and

select DSN (BIBLIO), or use connect string select RecordSource tab select Command Type (adCmdTable), select

Table name (Publishers)

Using DataGrid Control - 2

click toolbar's DataGrid, draw on formusing regular Properties window, set DataSource to connection being usedthen right click on DataGrid, select Retrieve fields


DataGrid properties use regular Properties window to set

some properties e.g., Caption

right click on grid for Properties Pages for others

General tab ColumnHeaders – on or off Enabled – allows user to scroll, select, modify AllowAddNew, AllowDelete, or AllowUpdate –

user can add, delete, or change database contents


Properties Pages (continued)Keyboard tab allow use of arrow keys set TabAction tab key behavior (

reference)

other tabs Color, Font, Format (number,

date/time, + etc. like in Excel)

Editing a DataGrid

right click grid, select Edit, right click again use commands to change grid

cut, paste, delete, etc. can split a grid to get a new user

windowuse Property Pages Layout tab to

uncheck Visible for individual columns in different splits

Using ActiveX Data Objects

Project>References> and then check: Microsoft ActiveX Data Objects 2.x Library

e.g., x = 2.7 if you have it provides ADOR (recordset) objects

Recordset, Field and Property objects provides ADODB objects

above objects plus Connection, Command, Parameter and Error objects

Set Up a Data Source in Code

can use a connection object to access a database with a DSNDim cn As ADODB.Connection

Set cn = New ADODB.Connectioncn.ConnectionString="DSN=[name]"

cn.Open

Setting Up a Data Source - 2

connecting without a DSN (p. 629)Dim cn As ADODB.Connection '(General)

Set cn = New ADODB.Connection

cn.ConnectionString = _

"Driver=Microsoft Access Driver

(*.mdb);DBQ=C:\[path]\[file].MDB;"

'need just one space before (*.mdb)

'NO spaces!! in Driver=Microsoft...

cn.Open

Using Recordsets in Code

Dim cn As ADODB.Connection

Dim rs[name] As ADODB.Recordset

'add to (General Declarations)

Set cn = New ADODB.Connection

cn.ConnectionString = _

"Driver=Microsoft Access Driver

(*.mdb);DBQ=C:\[path]\[file].MDB;"

cn.Open

Using Recordsets in Code - 2

Const sSQL = "SELECT * FROM [table]"

Set rs[name] = New ADODB.Recordsetrs[name].ActiveConnection = cnrs[name].Source = sSQLrs[name].Openrs[name].MoveFirstPrint "[ ]= " & _ rs[name].Fields("[field]")

Multiple Ways to Use Objects

Set rs[name] = New ADODB.Recordset

rs[name].ActiveConnection = cn

rs[name].Source = sSQL

rs[name].Open

ORSet rs[name] = cn.Execute(sSQL)

Recordset Lock Types

rs[name].LockType = … adLockReadOnly – can't add, change,

or delete adLockPessimistic – record locked

while working on it adLockOptimistic – record locked when

submitted to database (but rejected if another user already has a lock on it)

adLockBatchOptimistic – multiple records submitted, locked individually while being updated

Recordset Cursor Types

rs[name].CursorType = … adOpenForwardOnly – fast, but one-way adOpenKeySet – user can see changes by

other users, but not new records or deletions

adOpenDynamic – slowest, but user can see all modifications by other users

adOpenStatic – can't see any modifications

Updating Databases with Recordsets in ADO

Set rs[name] = New ADODB.Recordset

rs[name].CursorType = [ ]

rs[name].LockType = [ ]

rs[name].Source = [table, SQL]

rs[name].ActiveConnection = cn

rs[name].Open

Updating Databases with Recordsets in ADO - 2

'changing field values

rs[name].Fields("[field]") = [ ]

rs[name].Update '1 command

'need 2 commands to change in DAO

'adding new records (2 commands)

rs[name].AddNew '1st command

rs[name].Fields("[field]") = [ ]

rs[name].Update '2nd command

Disposing of Objects

to conserve resources, get rid of objects when finished with them

rs[name].Close 'disconnects from databaseSet rs[name] = Nothing

'removes from memorycn.CloseSet cn = Nothing

Data Source Name (DSN)

DSNs allow you to set up "virtual addresses" on a computer DSN "points to" the actual physical path

can change physical path for a DSN (e.g., when move application to another computer) but use same DSN in code

DSNs can make applications more portable but DO NOT use DSNs in your projects for

CIS 338 (they are not on my computer!)

cis 338: using ado (activex data objects) [largely replaced by adonet.vb] dr. ralph d. westfall...

Documents