Th e SqlD a t a Ada pt e r Cla ss a n d t h e D a t a Se t Cla ss in Visual Basic .NET

Paint Data Matrix 2d barcode in Visual Basic .NET Th e SqlD a t a Ada pt e r Cla ss a n d t h e D a t a Se t Cla ss

You use obj ect s based on t he SqlDat aAdapt er class in com binat ion w it h obj ect s based on t he Dat aSet class. A Dat aSet obj ect , which is an inst ance of t he Dat aSet class, represent s an in- m em ory cache of dat a ret r iev ed from a dat abase. The Dat aSet obj ect offers a disconnect ed dat a source as opposed t o t he alw aysconnect ed dat a source for SqlDat aReader obj ect s. As a consequence, using t he SqlDat aAdapt er and Dat aSet obj ect s inst ead of a SqlDat aReader obj ect im prov es applicat ion scalabilit y. This scalabilit y im prov em ent result s because t he Dat aSet doesn t persist a connect ion t o it s underly ing dat a source ov er t he w hole of it s lifet im e as does t he SqlDat aReader obj ect . While t he SqlDat aReader isn t as scalable as t he SqlDat aAdapt er / Dat aSet com binat ion, t he SqlDat aReader can prov ide fast er per form ance from a rem ot e dat a source because it deliv ers dat a in t he st yle of a forward- only, r ead- only cursor t he classic fir ehose deliv er y m odel.

The t er m firehose refers t o t he fact t hat dat a gushes out of a forward- only, read- only cursor.

The SqlDat aAdapt er and Dat aSet obj ect s com bine t o enable bot h dat a access and dat a m anipulat ion capabilit ies. This is im port ant because SqlDat aReader obj ect s prov ide st rict ly dat a access capabilit ies ( t hat is, you cannot perform updat e,

insert , or delet e t asks w it h a SqlDat aReader obj ect ) . Use t he SqlDat aAdapt er Fill m et hod t o populat e a Dat aSet obj ect wit h values from a SQL Ser ver dat a source. Because a single Dat aSet obj ect can work w it h m ult iple SqlDat aAdapt er and OLE DB Dat aAdapt er obj ect s, y ou can populat e a single Dat aSet obj ect w it h het er ogeneous dat a sources fr om m ult iple dat abase serv ers. For exam ple, y ou can populat e a single dat a set wit h t ables, v iews, or st or ed procedures from t wo different SQL Serv er inst ances or from Access and Oracle dat a sources in addit ion t o a SQL Server dat a source. Furt herm or e, you can j oin all t he dat a sources wit hin a Dat aSet obj ect on fields w it h com m on dat a t ypes. Use t he SqlDat aAdapt er Updat e m et hod t o t ransfer changes from a Dat aSet obj ect t o it s under ly ing dat a sources. When users per form insert , updat e, and delet e operat ions against t he cont ent s of a Dat aSet obj ect , t hose m odificat ions don t t ransfer t o t he dat a sources for t he Dat aSet obj ect unt il your applicat ion inv okes t he Updat e m et hod for a SqlDat aAdapt er obj ect underly ing t he dat a source. Despit e it s nam e, t he Updat e m et hod can process all t hree t ypes of dat a m anipulat ion operat ions. How ev er , y ou need a cust om SqlCom m and obj ect t o accom m odat e each t ype of dat a m anipulat ion t ask. Therefore, a SqlDat aAdapt er can r elat e t o a r em ot e dat a source t hr ough m or e t han a single SqlCom m and obj ect . Bet ween t he t im e y ou populat e t he Dat aSet obj ect and t he t im e your applicat ion inv ok es t he SqlDat aAdapt er Updat e m et hod, it s possible for t he underly ing dat a source on a SQL Ser ver inst ance t o change. Any changes can cause ex cept ions because t he or iginal values in a dat a set can be differ ent fr om t he cur rent values in t he SQL Server dat a source. The SqlDat aAdapt er has ev ent s and propert ies t o help m anage except ions t hat can occur dur ing an updat e process. Figure 1- 4 pr esent s a schem at ic diagram sum m ar izing how SqlDat aAdapt er and Dat aSet obj ect s exchange dat a wit h an under ly ing dat a source. By cont rast ing t his diagram w it h t he one in Figure 1- 3, you can easily spot an im port ant differ ence bet w een t he SqlDat aReader and a Dat aSet obj ect supplied by a SqlDat aAdapt er obj ect . The capabilit y of per form ing dat a m anipulat ion w it h t he Dat aSet obj ect is a cr it ical feat ur e t hat m eans m any applicat ions w ill rely on a Dat aSet obj ect inst ead of a SqlDat aReader obj ect . Figu r e 1 - 4 . A sch em a t ic illu st r at in g t h e rou t e by w h ich SqlD a t aAd a pt er a n d D a t a Set obj e ct s e xch a n g e va lu es w it h a SQL Se rv e r da t a sou r ce .

The Dat aSet obj ect offers an obj ect m odel for m anaging t he indiv idual elem ent s wit hin it . The Dat aSet obj ect consist s of a Dat aTable collect ion ( along wit h ot her elem ent s) . This collect ion can cont ain one or m ore t ables. You can creat e t hese t ables w it h t he SqlDat aAdapt er Fill m et hod w hen y ou init ially populat e a Dat aSet obj ect from a SQL Serv er dat a source. The Select Com m and pr opert y , which is a T- SQL st at em ent or a st or ed procedure, for a SqlDat aAdapt er obj ect can serv e as t he basis of a t able in t he Dat aTable collect ion for a Dat aSet obj ect . You can use m ult iple SqlDat aAdapt er obj ect s t o add m or e t han one t able t o a Dat aSet obj ect . Each t able has a r ich obj ect m odel t hat perm it s t he designat ion of pr im ary keys and for eign k eys as well as const raint s t o m anage dat a int egrit y w it hin a t able. One very pract ical use for t he Dat aTable collect ion and t he obj ect m odel for indiv idual t ables is t hat you w ill use it t o nav igat e am ong t he values wit hin a Dat aSet obj ect .