a brief introduction to ado.net web forms

8/10/2019 A Brief Introduction to ADO.NET Web Forms

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.NET Web Forms

ADO .NET Introduction

K
http://www.apextgi.in/http://www.apextgi.in/http://www.apextgi.in/


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ADO .NET Overview

ASP .NET CodeDatabase

Web Form

Data Controls

Data Connector(Establishes connection and

opens the database.)

Data Adapter(Translates commands and

exchanges data.)

SQL

Dataa

nd

Errors

Data Set (Collection of tables and relationships.)

CustomerID

LastName

FirstName

Data Table Data !ie" (Based on 1 table.)

O#DE# $% LastName

W&E#E '

Data #elations(ip

(Associations among tables.)

Fill

Data $ind

)a*or +uestion, W(at

is missin-Hint: it is

missing in AD .!ET"

not #$st the diagram.

Ans%er: sa&e data


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Sample Project: Simple2

%ou s(ould create a ne" sample pro*ect to test /our s0ills.

T(e completed 1ersion s(ould loo0 somet(in- li0e, Simple2


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Data Connector T(e Data Connector is usuall/ strai-(t3or"ard.

T(e "i4ard starts automaticall/ "(en /ou add a Data Adapter.

C(oose t(e t/pe o3 database 5t(at pic0s t(e pro1ider and t(e speci3icconnector6.

Enter t(e connection in3ormation7usuall/ location.

Access, Speci3ic p(/sical pat(.

Oracle, Oracle connection in3ormation

#e-istered name8ser name

8ser pass"ord

SQL Ser1er connection in3ormation 5but use t(e SQL Adapter6

Ser1er

8ser name8ser pass"ord

SQL Ser1er (as man/ s(ortcutsand tric0s "it(in !isual Studio

T(e connector simpl/ establis(es t(e communication lin0s to t(e

database.


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Data Connector Callen!es ADO .NET di33iculties

Access problem is t(at it is (ard to c(an-e t(e location later.

It is also di33icult to c(an-e databases later 5SQL Ser1er to Oracle6.

Partial Solution 5but critical6

Store all D$ speci3ic code in one place.

Do notscatter database code across /our application and 3orms.

$e3ore buildin- an/ database 3orms9 create a ne" blan0 Component

3or t(e sole purpose o3 (oldin- all primar/ database de3initions.

Solution E:plorer ; Add ; Add Ne" Item ; Component Class, D$)ain

To create a database connection9 simpl/ dra- one onto t(e desi-n

screen o3 t(e ne" component9 and 3ill in t(e "i4ard properties.

Select a pro1iderAccess,

Oracle, Oracle Pro1ider 3or OLE D$ 5ma/be )icroso3t 1ersion6

SQL Ser1er, 8se t(e SQL Adapter instead?

#ename t(e connector, cnnOle


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T"F: Tin!s "icroso#t For!ot

I de1eloped some standard routines to (andle se1eral common

issues. T(e/ are stored in a class called T)F. %ou "ill e1entuall/ end up addin- t(is class to most o3 /our 3orms.

First9 add t(e 3ile to /our pro*ect9 ri-(t@clic0 ; Add ; Add E:istin-,

T)F.1b 5/ou onl/ (a1e to do t(is once6.

Second9 3or an/ 3orm t(at /ou need t(e routines9 open t(e Code !ie"

5!ie" ; Code9 or ri-(t@clic06 add one line o3 code9 o3ten at t(e top9alon- "it( t(e control de3initions,

Dim tm3 As T)F B Ne" T)F56

Details o3 t(e routines "ill be e:plained in 3uture slides as t(e/ are

needed.

Notes and some documentation are "ritten as comments in t(e3ile.


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Data Connector: Access Fle$ibilit%

One problem "it( t(e Access connector is t(at it relies on a 3i:ed

pat(name9 ma0in- it di33icult to mo1e t(e database. %ou need to add t(e special T)F 5T(in-s )icroso3t For-ot6 component to

/our pro*ect 5Add ; E:istin- File6.

In t(e D$)ain component9 e:pand t(e Component Desi-ner eneratedre-ion9 in t(e Public Sub Ne"569 a3ter Initiali4eComponent9 add

Dim tm3 As Ne" T)F56

Dim strCS As Strin-strCS B tm3.etCnnStrin-5cnnOleCareer6

I3 5strCS 6 T(en )e.cnnOleCareer.ConnectionStrin- B strCS

In t(e Web.con3i- 3ile9 ri-(t be3ore t(e end Gcon3i-uration9 addGmodi3/

appSettin-s

?@@ 8ser application and con3i-ured propert/ settin-s -o (ere.@@?@@ E:ample, add 0e/Bsettin-Name 1alueBsettin-!alueG @@

add 0e/BcnnOleCareer.ConnectionStrin- 1alueB G

add 0e/BcnnOleCareer.DataSource 1alueB..GDatabaseGcareer.mdb G

GappSettin-s

T(is approac( uses a relati1e pat(9 so /ou can mo1e t(e entire pro*ect.


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Data A&apter Comments

Data Adapter

Is responsible 3or translatin- SQL re+uests to t(e c(osen t/pe o3database and returnin- data ro"s and messa-es.

E1er/ command or table t(at /ou "ant to access must be associated

"it( a data adapter.

Tec(nicall/9 a data adapter can (andle se1eral di33erent tables.

$ut9 unless t(e tables "ill be related 5parentGc(ild69 it seems easier tocreate a separate data adapter 3or eac( table.

$i--est dra"bac0 is t(at SQL Ser1er uses a di33erent data adapter

t(an AccessGOracle. So9 i3 /ou "ant to c(an-e D$)Ss later9 /ou (a1e

to replace all o3 t(e adapters?

Critical, Heep all data adapters in one 5ma/be t"o6 locations, t(e

D$)ain component.

Creatin- a data adapter

From t(e Data toolbo:9 dra- an adapter onto t(e main D$ component.

5Ole 3or Access or Oracle9 S+l 3or SQL Ser1er6.

Ans"er t(e "i4ard +uestions. To c(an-e later, Con3i-ure Data Adapter


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Create Data A&apter: '(er% T%pe

First9 c(oose /our database

connection 5not s(o"n (ere6. Second9 c(oose t(e t/pe o3

+uer/ to use.

Access onl/ supports te:t

SQL.

SQL Ser1er and Oracle "ill-enerall/ run 3aster i3 /ou use

a stored procedure9 "(ic( is

a parameteri4ed 1ie" stored

and precompiled on t(e

database ser1er.

I3 /ou let t(e "i4ard build t(eprocedure9 /ou s(ould -o

bac0 to t(e database and

double@c(ec0 it.


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Create Data A&apter: '(er% T%pe

Create t(e SQL statement to

retrie1e t(e data 3rom tablesor e:istin- 1ie"s.

8se t(e Quer/ $uilder to

minimi4e t/pin- errors.

Warnin-, i3 /ou pull data 3rom

more t(an one table 5or 3rom a1ie" t(at uses more t(an one

table69 .NET "ill not be able to

edit t(at data.

Quer/ $uilder 5ne:t slide6

Ad1anced Options 5slide6


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Data A&apter: '(er% )(il&er

Add tables

Clic0 columns to add, Warnin-9t(e/ are displa/ed in t(e orderin "(ic( /ou add t(em. %oucan mo1e t(em later9 but it iseasier to do it ri-(t no".

Note t(at columns t(at arereser1ed "ords s(ould usebrac0ets. W(en in doubt9 usebrac0ets.

I3 /ou use more t(an one table9.NET "ill not be able to edit t(e

data. I3 /ou


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Data A&apter: A&vance& Options I3 /ou onl/ need to retrie1e data 5not

c(an-e it69 unc(ec0 all o3 t(ese

options.

In some situations9 /ou "ill "ant to

s0ip t(e optimistic concurrenc/. I3

/ou unc(ec0 t(is bo:9 all c(an-es

"ill be "ritten to t(e database9 e1en

i3 someone else c(an-ed t(e data

immediatel/ be3ore /ou.

T(e t(ird option is onl/ a1ailable

"it( SQL Ser1er and Oracle

5databases t(at support +uer/

lan-ua-es t(at can do more t(anone t(in-6. 8se3ul i3 /ou insist on

usin- Identit/ 5AutoNumber6

columns and need to insert ro"s.


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Data Set Overview

A Data Set is rou-(l/ a miniature in@memor/ cop/ o3 part o3 /our

database. %ou speci3/ "(ic( tables /ou "ant to include.

%ou can build relations(ips 5usuall/ parentGc(ild6.

%ou can create Data !ie"s9 but data 1ie"s are not+ueries. T(e/

cannot per3orm


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Data Set: +enerate

Once t(e adapter is created9 it is

eas/ to -enerate a data set in t(emain D$ component.

#i-(t@clic0 on t(e adapter.

enerate Data set

Select Ne" and enter a uni+ue

data set name. )a0e sure t(e proper table is

c(ec0ed.

C(ec0 t(e bo: to add it to t(e

desi-ner.

I3 /ou need to delete a dataset9/ou "ill (a1e to delete it 3rom

t(e .:sd list o3 3iles 5and delete it

3rom t(e D$ code6.


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Wat We ,ave So Far

A Data Connection t(at can open t(e database

A Data Adapter t(at can send SQL to t(e database and recei1edata ro"s.

A de3inition o3 a Data Set t(at can temporaril/ (old data t(at is

read 3rom one table 5or 1ie"6.

%ou can add ot(er adapters and datasets.

%ou can create relations(ips i3 t(ere are parentGc(ild tables9 but /ou"ill see t(at t(ese are not 1er/ use3ul.

T(in-s "e do not (a1e /et.

T(ere is no data in t(e data set.

T(e data set is not connected to t(e 3orm


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Fillin! te Data Set

In t(e main D$ component 5!ie" ; Code6 add a subroutine,

Public Sub FillEmplo/ee5$/!al ds As DataSet6adpEmplo/ee.Fill5ds6

End Sub

At 3irst -lance9 t(e routine seems pointless9 but its purpose is to0eep t(e database@speci3ic code in one component. #emember

t(at t(e adapter is speci3ic to t(e database. T(is "a/9 /our 3orm

can use t(e dataset onl/9 "(ile t(e adapter sta/s in t(e one

component.

We "ill add code to /our data 3orm to call t(is routine.


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Creatin! te Data Form

T(ree basic t/pes o3 3orms are commonl/ used in business

applications. Eac( (as sli-(tl/ di33erent considerations and setup.T(e/ "ill be co1ered in later lessons.

Consider a standard 3orm "it( one ro" o3 data.

To start9 add a ne" blan0 Web Form9 named Emplo/ee

Drop a Data Set onto t(e blan0 desi-n. Select t(e emplo/ee data

set /ou created earlier. T(en do !ie" ; Code to see t(e code. %ou need to tell t(e 3orm to -o to t(e database and 3ill t(e data set

"it( data. T(ere are t"o possible timesGplaces to do t(is,

Pa-eLoad or Pa-eInit. For no"9 Pa-eLoad is easier.

Near t(e top o3 t(e class9 add,

Protected cmp)ain as Ne" D$)ain56

Protected tm3 As Ne" T)F56

In t(e Sub Pa-eLoad9 add,

cmp)ain.FillEmplo/ee5DsEmplo/eeJ6


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Startin! te Data Form Pa!e

Add a st/le. Open t(e st/le s(eet and add a class 3or Pa-eTitle

C(oose a 3ont 3amil/ 5e.-.9 Arial6 and 3ont si4e 5e.-.9 2 em6 In Te:t9 set t(e (ori4ontal ali-nment to Centered

Sa1e and close t(e st/le s(eet and drop it onto t(e data 3orm.

Add a Title. From t(e Web Forms toolbo:9 Drop a Label near t(e top o3 t(e 3orm

In t(e Te:t propert/9 enter t(e title, Emplo/ee

Set t(e CssClass, Pa-eTitle

C(an-e t(e ID, lblPa-eTitle 5not strictl/ re+uired9 but a use3ul (abit6

Lin0 t(e pa-e. Open t(e main 3orm 5rename it9 e.-.9 AAStart6Add t(e st/le s(eet and a title.

Add a &/perLin0 t(at opens t(e data 3orm.

Set, Te:t 5Emplo/ee Form69 ID 5ln0Emplo/ee69 Na1i-ate8#L5Emplo/ee.asp:6

Sa1e e1er/t(in- and build and bro"se to test it. I3 t(e D$ 3ormcras(es9 c(ec0 t(e securit/ settin-s 3irst.


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A&&in! Data Controls

Desi-n 1ie" on t(e data 3orm.

Dra- and drop labels and te:t bo:es onto t(e 3orm. Heep a list (and/ 3or t(e data columns.

For labels9 set properties

ID, lblColumnlblEmplo/eeID

Te:t, Column Emplo/ee ID

For te:t bo:es9 set properties ID, t:tColumnt:tEmplo/eeID

Tab Inde: Number 3rom top to bottom 5> ' K6

Add a $utton9 Call it Sa1e 5IDBbtnSa1e6 5Do not "rite code 3or it /et6.

8se Format )enu to 1erticall/ space and ali-n e1er/t(in-.

Data bindin- t(e controls For eac( te:t bo:9 clic0 t(e Data $indin- propert/

C(oose simple bindin-9 and clic0 /our "a/ do"n t(e list until /ou can

select t(e matc(in- column. 5See ne:t slide6


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Simple Data )in&in!

)a0e sure Te:t

propert/ is selected

on t(e le3t.

Clic0 /our "a/ do"n

t(e list on t(e ri-(tuntil /ou can select

t(e matc(in- data

column.

%ou can set a

3ormat9 3or e:ample

3or dates.


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Activate Data )in&in!

T(e control properties simpl/ set a mappin- 3rom t(e dataset

table to t(e control. %ou still need to acti1ate t(e bindin- and trans3er t(e data.

Eac( control (as a Data$ind met(od t(at per3orms t(is one@"a/trans3er.

$ut9 it is easier to use t(e Pa-e.Data$ind met(od because it does t(e

trans3er 3or all o3 t(e controls. T(e problem,

Callin- Data$ind replaces t(e content o3 tar-et9 destro/in- "(ate1er"as t(ere be3ore.

Forms use a Post$ac0 approac(. W(en users clic0 a button9 t(e data

is sent bac0 to t(e same pa-e. %ou must a1oid destro/in- t(e datac(an-ed b/ t(e user.

In Pa-eLoad9 add,

Test it

I3 Not Pa-e.IsPost$ac0 T(en

Pa-e.Data$ind56

End I3


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Savin! Data: Te Simple Approac W(en /ou created t(e data adapter9 b/ de3ault9 it created SQL

statements to 8pdate9 Insert9 and Delete.

I3 t(e data in t(e in@memor/ data set c(an-es9 ADO .Net canautomaticall/ appl/ t(e c(an-es 5includin- insert and delete6 bac0 to

t(e stored database.

First9 in t(e )ain database component9 add,

Public Sub 8pdateEmplo/ee5$/!al ds As DataSet6

adpEmplo/ee.8pdate5ds6End Sub

In t(e data 3orm9 "rite code 3or t(e Sa1e button to trans3er t(e 3orm

data to t(e data set. Double@clic0 t(e Sa1e button to start. Add,DsEmplo/eeJ.Tables5Emplo/ee6.#o"s5>6.$e-inEdit56

DsEmplo/eeJ.Tables5Emplo/ee6.#o"s5>65Emplo/eeID6 B t:tEmplo/eeID.Te:tDsEmplo/eeJ.Tables5Emplo/ee6.#o"s5>65LastName6 B t:tLastName.Te:t

' 5do all o3 t(e columns6

DsEmplo/eeJ.Tables5Emplo/ee6.#o"s5>6.EndEdit56

cmp)ain.8pdateEmplo/ee5DsEmplo/eeJ6


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Problems wit te Simple Approac

We (a1e i-nored concurrenc/ issues.

It "ould actuall/ be better i3 /ou build t(e dataset "it(out testin- 3orconcurrenc/.

#i-(t no"9 i3 someone else c(an-es t(e data9 t(e update "ill cras(9 and

cannot be reco1ered unless /ou bac0 out o3 t(e 3orm and reload t(e data

3rom t(e database.

&o"e1er9 notice t(at e1er/ time t(e 3orm is loaded9 includin- durin- post

bac09 t(e pa-e -oes to t(e database and -ets t(e current 1ersion. So9 t(is

1ersion "ill actuall/ o1er"rite most c(an-es made b/ ot(er people "it( no

"arnin-. T(e onl/ concurrenc/ issue t(at "ill be cau-(t and cras(ed is on

t(e ser1er bet"een re@readin- t(e pa-e and "ritin- t(e ne" data "(ic( is

a relati1el/ minor c(ance.

It "ill be incredibl/ borin- to duplicate t(ese steps 3or e1er/ 3orm /ou"ill (a1e. It "ill also be pain3ul to return later and ma0e c(an-es.

Note t(at t(e dataset is not sa1ed across post bac0. W(ic( is probabl/

-ood9 since t(e s/stem is desi-ned to read t(e entire table. W(ic( is

cra4/9 since t(e 3orm onl/ uses one ro" at a time.


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C(stomer Form: A )etter "eto& It is pointless and pain3ul to (a1e to "rite t(e same comple: update

code e1er/ time /ou need a 3orm. So9 I created some -eneric routines

to (elp. T(is e:ample relies (ea1il/ on t(em. )a0e sure /ou (a1e t(e T)F 3ile in /our pro*ect.

Cop/ t(e -eneric code 3rom t(e D$)ain in t(e sample pro*ect. 5especiall/

$atc(8pdate and )er-eConcurrenc/6

ettin- started

Create t(e Data Adapter in D$)ain as usual9 be sure to ta0e t(e de3ault to-enerate optimistic concurrenc/.

enerate t(e Data Set as usual. Heep a cop/ o3 t(e column names.

Add t"o routines to t(e D$)ain code,

Public Sub FillCustomer5$/!al ds As DataSet9 $/!al sID As Strin-6

Dim tm3 As T)F B Ne" T)F56 adpCustomer.SelectCommand.CommandTe:t B

tm3.AddW(ereToSelect5adpCustomer.SelectCommand.CommandTe:t9 CustomerIDB sID6

adpCustomer.Fill5ds6

End Sub

Public Function 8pdateCustomer5$/!al ds As DataSet9 $/!al sID As Strin-6 As Strin-

#eturn $atc(8pdate5ds9 adpCustomer9 Customer9 AddressO3 )e.FillCustomer9

sID6

End Function


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C(stomer Form: Constr(ction

Create a ne" Web Form 3or Customer.

Add t(e st/le s(eet and Pa-e TitleAdd t(e data set

Add t(e labels and te:t bo:es9 set t(e tab inde:

8se Data$indin- to lin0 t(e te:t bo:es to t(e dataset.

Add t(e Sa1e button 5do not "rite code /et6

Add a blan0 Label at t(e top9 across t(e pa-e9 ID, lbl)essa-e

!ie" ; Code9 belo" t(e control de3initions 5Protected Wit(E1ents6

Protected cmp)ain As D$)ain B Ne" D$)ain56

Protected tm3 As tm3 B Ne" tm356


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C(stomer Form: ar%Col(mns

T(e -eneric code needs a met(od to map t(e column names to

t(e controls. T(e easiest met(od is to create a special arra/ abo1et(e Pa-eLoad routine. For eac( column9 /ou enter

Column Name

Control ID

T/pe o3 control 5Te:t9 Label9 DDL9 C(ec06

W(et(er or not t(e column is part o3 t(e primar/ 0e/

Pri1ate ar/Columns56 As tm3.Sin-leEditItem B M

Ne" tm3.Sin-leEditItem5CustomerID9 t:tCustomerID9 Te:t9

True69

Ne" tm3.Sin-leEditItem5FirstName9 t:tFirstName9 Te:t9 False69

Ne" tm3.Sin-leEditItem5LastName9 t:tLastName9 Te:t9 False69

Ne" tm3.Sin-leEditItem5Address9 t:tAddress9 Te:t9 False69

' Do all o3 t(e columns '

Ne" tm3.Sin-leEditItem5E)ail9 t:tEmail9 Te:t9 False69

Ne" tm3.Sin-leEditItem58#L9 t:t8#L9 Te:t9 False6


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C(stomer: Pa!e-oa&

T(e main c(an-e to Pa-eLoad is t(at it onl/ reads 3rom t(e

database t(e 3irst time t(e pa-e is loaded 5not durin- Post$ac069and t(e dataset (as to be sa1ed in a Session so "e can (an- onto

t(e ori-inal 1alues.

Also notice t(at t(e Fill routine (as been modi3ied to read onl/ one

ro" o3 data.

I3 Not Pa-e.IsPost$ac0 T(en

cmp)ain.FillCustomer5DsCustomerJ9 J6

Session5dsCustomerJ6 B DsCustomerJ

Pa-e.Data$ind56

Else

DsCustomerJ B CT/pe5Session5dsCustomerJ69 dsCustomer6

End I3


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C(stomer: btnSave Sa1in- t(e data is no" (andled b/ t(e -eneric routines. Add t(e

3ollo"in- code to t(e btnSa1eClic0 routine,

T(e 3irst routine copies t(e data 3rom t(e 3orm to t(e dataset 5usin-

t(e ar/Columns mappin-6. T(e second routine does t(e update9 and c(ec0s 3or concurrenc/.

W(at (appens i3 t(ere is a concurrenc/ collision Tr/ it.

W(ere are t(e underl/in- 1alues stored T(e/ are 0ept as properties

"it(in t(e dataset table.

T(e routine re@reads t(e database9 and replaces t(e underl/in- 1alues"it( t(e ne" current 1alues. &o"e1er9 it lea1es t(is users c(an-es on t(e

3orm. So clic0in- Sa1e a second time "ill 3orce update t(e database i3

t(ere "as a concurrenc/ error.

%ou reall/ need to add some messa-e and probabl/ more c(oices to t(e

user. $ut t(at is a user inter3ace decision.

tm3.Cop/FormToDataSet5)e9 ar/Columns9 DsCustomerJ9 Customer9 >6

lbl)essa-e.Te:t B cmp)ain.8pdateCustomer5DsCustomerJ6


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C(stomer: State DropDownist

To pro1ide a drop do"n list 5selection bo:6 3or states9 /ou 3irst need to

create a table o3 StateCodes9 "it( t(e state and t(e name. 8sers "ill seet(e names 5alp(abeti4ed69 and t(e t"o@letter state code "ill be insertedinto t(e database.

Second9 create a ne" data adapter and dataset. #etrei1e StateCode and Name9 sorted.

Deselect t(e build update.

Create t(e FillStateCodes routine.

Customer 3orm9 delete t(e e:istin- state te:t bo:Add t(e StateCodes data set9 t(en add a DDL and set its tab inde:

ID ddlState

DataSource DsStateCodesJ

Data)ember StateCodes DataTe:tField, Name

Data!alueField State

In t(e ar/Columns arra/9 c(an-e t(e control t/pe to DDL and ID to ddlState

In Pa-eLoad9 3ill t(e ne" dataset

cmp)ain.FillStateCodes5DsStateCodesJ6


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DD: Tric/% T"F

)icroso3t did not bot(er to create a simple mec(anism to -et drop

do"n lists to displa/ t(e currentl/ assi-ned 1alue. For instance9 i3t(e database state 1alue is CT9 /ou "ant t(e bo: to start "it( a

displa/ o3 Connecticut.

So9 turn to t(e trust/ T)F class 3or (elp.

In properties 3or t(e DDL9 clic0 t(e Data $indin-s button.

)a0e sure /ou c(oose t(e SelectedInde: on t(e le3t side? C(oose custom bindin-9 and add, 5Its t(at eas/9 see ne:t slide6

tm3.SelectDe3aultDDL5sender9 DsStateCodesJ9 Data$inder.E1al5DsCustomerJ9

TablesRCustomer.De3ault!ie".R>.State66

Dataset name t(at (olds t(e DDL list

Dataset name 3or t(e o1erall 3orm

Column name 3rom t(e o1erall 3orm t(at (olds t(e de3ault 1alue

Table name 3or t(e o1erall 3orm


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DD )in&in! #or Selecte&0n&e$


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C(stomer Form


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Te Form is Still not 1sable

T(e -eneric code can be used 3or an/ 3orm. T(e ar/Columns arra/

is t(e 0e/ to pro1idin- t(e in3ormation t(e subroutines need. %ou reall/ need to t(in0 about a user inter3ace to e:plain (o" to

(andle concurrenc/ collisions. T(e -rid code 5later6 s(o"s one

"a/ to (andle t(e problem. $ut 3eel 3ree to e:periment9 t(ere are

no -reat solutions /et.

Se1eral steps remain to ma0e t(is a use3ul 3orm. Selectin- a customerGro" 5tric0/9 depends on user inter3ace -oals6

Findin- a customer 5moderatel/ tric0/ code6

Addin- a ne" customer 5relati1el/ eas/6

Deletin- a customer 5eas/9 until /ou (a1e to s(o" t(e ne:t customer6

Securit/ 5relati1el/ eas/9 but re+uires more 3orms6 )ore


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Conc(rrenc% &o" does t(e update command (andle optimistic concurrenc/

T(e SQL command uses t(e ori-inal 1alue 3or eac( column in its

W(ere clause. $ut "(ere does it -et 5and store6 t(e ori-inal 1alue9 "(ic( is t(e 1alue

t(at e:isted "(en t(e data ro" "as retrie1ed

Ans"er, t(e data ro" (olds multiple 1ersions o3 eac( data column.%ou can access t(em "it( Data#o"!ersion enumeration.

I3 t(ere is a concurrenc/ problem9 t(e $atc(8pdate routineretrie1es t(e current 1alue and places it into t(e Ori-inal 1alue. Itlea1es t(e current users 1alue as t(e primar/Gcurrent 1alue. %oucan compare t(ese 1alues in eac( column to see "(ere t(eproblem "as and s(o" bot( 1alues.

Set IDB t(e primar/ 0e/ 1alue o3 t(e ro" bein- edited

Dim ds#o" As Data#o" B Ds)ineJ.Tables5)/Table6.#o"s.Find5ID6

C(ec0 eac( columnGloop

I3 5ds#o"5*6 ds#o"5*9 Data#o"!ersion.Ori-inal66 T(en

Displa/ concurrenc/ errorG1alue

End I3


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C(stomer: A&& Co&e

Public Function AddCustomer5$/!al ds As DataSet6 As Strin-

Dim cID As Inte-er B enHe/5Customer6

Dim str)s- As Strin-

I3 5cID >6 T(en

str)s- B 8nable to -enerate a ne" Customer ID.

End I3

Dim dr As Data#o" B ds.Tables5Customer6.Ne"#o"56

dr5CustomerID6 B cID ds.Tables5Customer6.#o"s.Add5dr6

str)s- B 8pdateCustomer5ds9 cID6

ds.Clear56 U Clear t(e data set and reload *ust t(e one ne" ro"

ds.AcceptC(an-es56 U Need to tell it not to delete t(e ori-inal ro"

FillCustomer5ds9 cID6

#eturn str)s-End Function

enHe/ is anot(er -eneric routine /ou need to add to /our

D$)ain. I3 /ou are runnin- under Oracle9 re"rite enHe/ to

use Se+uences.


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C(stomer: Delete Co&e

T(e Delete code is muc( tric0ier9 because "e need to -uess "(ic(

CustomerID to displa/ ne:t9 and bad t(in-s (appen to t(e 3orm i3"e delete all o3 t(e ro"s in t(e dataset.

Public Function DeleteCustomer5$/!al ds As DataSet6 As Strin-

Dim sID As Strin- B ds.Tables5Customer6.#o"s5>65CustomerID6

Dim str)s- As Strin-

U T(e (ard part, W(at customer do I load ne:t U Tr/ 3indin- *ust t(e 3irst customer sorted b/ ID

Dim rdr As OleDb.OleDbData#eader

Dim cmd As OleDb.OleDbCommand B Ne" OleDb.OleDbCommand56

cmd.CommandTe:t B SELECT CustomerID F#O) Customer O#DE# $% CustomerID

cmd.Connection B )e.cnnOleSimple

cnnOleSimple.Open56

Dim cID As Inte-er


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C(stomer: Delete Co&e 2

Tr/

rdr B cmd.E:ecute#eader5Command$e(a1ior.De3ault6 rdr.#ead56

cID B CT/pe5rdr5CustomerID69 Inte-er6

I3 5cID B CT/pe5sID9 Inte-er66 T(en U I3 delete Jst one9 tr/ to -et t(e ne:t ro"

rdr.#ead56

cID B rdr5CustomerID6

End I3 rdr.Close56

Catc( e2 As E:ception

cID B @J

str)s- B No customers remain. Please add at least one.

End Tr/

cnnOleSimple.Close56


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C(stomer: Delete Co&e

Tr/

ds.Tables5Customer6.#o"s5>6.Delete56 I3 5cID @J6 T(en

8pdateCustomer5ds9 cID.ToStrin-6

Else

8pdateCustomer5ds9 Not(in-6

End I3

str)s- B Deleted customer sID

Catc( e As E:ception

str)s- B Error deletin- customer. e.)essa-e

End Tr/

I3 5cID B @J6 T(en U Dataset can ne1er be empt/ or 3orm "ill cras(

Dim dr As Data#o" B ds.Tables5Customer6.Ne"#o"

dr5CustomerID6 B @J ds.Tables5Customer6.#o"s.Add5dr6

End I3

#eturn str)s-

End Function


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S(mmar%

T(e 3orm is -ettin- closer.

It still needs to be "it(in an application9 t(at can (andle t(in-s li0eselectin- a customer and securit/.

$ut9 buildin- se1eral 3orms o3 t(is t/pe 3or an application is still

-oin- to be pain3ul9 "it( lots o3 repetition.

8ltimatel/9 it "ould be nicer i3 a data "i4ard e:isted to build most o3

t(e -eneric code automaticall/. Lac0in- t(e time to "rite suc( a "i4ard9 t(e ne:t best step is to

create a set o3 -eneric templates9 t(at can be copied and used to

+uic0l/ build 3orms t(at (andle standard problems.


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