DAORDOADO
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ADOisn'tautomaticallycode-compatiblewithyourexistingdataaccessapplications.WhileADOencapsulatesthefunctionalityofDAOandRDO,youmustconvertmanyofthelanguageelementsovertoADOsyntax.Insomecases,thiswillmeanonlyasimpleconversionofsomefunctionsofyourexistingcode.Inothercases,itmightbebesttorewritetheapplicationusingADO'snewfeatures.
DAO(DataObjects)wasthefirstobject-orientedinterfacethatexposedtheMicrosoftJetdatabaseengine(usedbyMicrosoftAccess)andalloweddeveloperstodirectlyconnecttoAccesstables-aswellasotherdatabases-throughODBC.DAOissuitedbestforeithersingle-systemapplicationsorforsmall,localdeployments.
RDO(RemoteDataObjects)isanobject-orienteddataaccessinterfacetoODBCcombinedwiththeeasy-to-usestyleofDAO,providinganinterfacethatexposesvirtuallyallofODBCslow-levelpowerandflexibility.RDOislimited,though,inthatitdoesn'taccessJetorISAMdatabasesverywell,andthatitcanaccessrelationaldatabasesonlythroughexistingODBCdrivers.However,RDOhasproventobetheinterfaceofchoiceforalargenumberof,,andotherlargerelationaldatabasedevelopers.RDOprovidestheobjects,properties,andmethodsneededtoaccessthemorecomplexaspectsofstoredproceduresandcomplexresultsets.
ADOisthesuccessortoDAO/RDO.FunctionallyADO2.0ismostsimilartoRDO,andthere'sgenerallyasimilarmappingbetweenthetwomodels.ADO"flattens"theobjectmodelusedbyDAOandRDO,meaningthatitcontainsfewerobjectsandmoreproperties,methods(andarguments),andevents.Forexample,ADOhasnoequivalentstotherdoEngineandrdoEnvironmentobjects,whichexposedtheODBCdrivermanagerandhEnvinterfaces.NorcanyoucurrentlycreateODBCdatasourcesfromADO,despitethefactthatyourinterfacemightbethroughtheODBCOLEDBserviceprovider.
MuchofthefunctionalitycontainedintheDAOandRDOmodelswasconsolidatedintosingleobjects,makingforamuchsimplerobjectmodel.Becauseofthis,however,youmightinitiallyfinditdifficulttofindtheappropriateADOobject,collection,property,method,orevent.UnlikeDAOandRDO,althoughADOobjectsarehierarchical,theyarealsocreatableoutsidethescopeofthehierarchy.
Itshouldbenoted,however,thatADOcurrentlydoesn'tsupportallofDAO'sfunctionality.ADOmostlyincludesRDO-stylefunctionalitytointeractwithOLEDBdatasources,plusremotingandDtechnology.
Ingeneral,it'sprobablytooearlyintheevolutionofADOtomigratemostDAOapplications(exceptpossiblyonesusingODBCDirect)toADOrightnow,sinceADOdoesn'tcurrentlysupportdatadefinition(DDL),users,groups,andsoforth.IfyouuseDAOonlyforclient-serverapplicationsanddon'trelyontheJetdatabaseengineoruseDDL,however,thenyoucanprobablymigratetoADOnow.Eventually,MicrosoftwillprovideanADODDLcomponenttoaidinDAO-to-ADOmigrationandprovidegenericDDLsupportforOLEDBproviders.1<script type="text/javascript"><!--google_ad_client = "pub-2947489232296736";/* 728x15, 创建于 08-4-23MSDN */google_ad_slot = "3624277373";google_ad_width = 728;google_ad_height = 15;//--></script><script type="text/javascript"src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>
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ADOisn'tautomaticallycode-compatiblewithyourexistingdataaccessapplications.WhileADOencapsulatesthefunctionalityofDAOandRDO,youmustconvertmanyofthelanguageelementsovertoADOsyntax.Insomecases,thiswillmeanonlyasimpleconversionofsomefunctionsofyourexistingcode.Inothercases,itmightbebesttorewritetheapplicationusingADO'snewfeatures.
DAO(DataObjects)wasthefirstobject-orientedinterfacethatexposedtheMicrosoftJetdatabaseengine(usedbyMicrosoftAccess)andalloweddeveloperstodirectlyconnecttoAccesstables-aswellasotherdatabases-throughODBC.DAOissuitedbestforeithersingle-systemapplicationsorforsmall,localdeployments.
RDO(RemoteDataObjects)isanobject-orienteddataaccessinterfacetoODBCcombinedwiththeeasy-to-usestyleofDAO,providinganinterfacethatexposesvirtuallyallofODBCslow-levelpowerandflexibility.RDOislimited,though,inthatitdoesn'taccessJetorISAMdatabasesverywell,andthatitcanaccessrelationaldatabasesonlythroughexistingODBCdrivers.However,RDOhasproventobetheinterfaceofchoiceforalargenumberof,,andotherlargerelationaldatabasedevelopers.RDOprovidestheobjects,properties,andmethodsneededtoaccessthemorecomplexaspectsofstoredproceduresandcomplexresultsets.
ADOisthesuccessortoDAO/RDO.FunctionallyADO2.0ismostsimilartoRDO,andthere'sgenerallyasimilarmappingbetweenthetwomodels.ADO"flattens"theobjectmodelusedbyDAOandRDO,meaningthatitcontainsfewerobjectsandmoreproperties,methods(andarguments),andevents.Forexample,ADOhasnoequivalentstotherdoEngineandrdoEnvironmentobjects,whichexposedtheODBCdrivermanagerandhEnvinterfaces.NorcanyoucurrentlycreateODBCdatasourcesfromADO,despitethefactthatyourinterfacemightbethroughtheODBCOLEDBserviceprovider.
MuchofthefunctionalitycontainedintheDAOandRDOmodelswasconsolidatedintosingleobjects,makingforamuchsimplerobjectmodel.Becauseofthis,however,youmightinitiallyfinditdifficulttofindtheappropriateADOobject,collection,property,method,orevent.UnlikeDAOandRDO,althoughADOobjectsarehierarchical,theyarealsocreatableoutsidethescopeofthehierarchy.
Itshouldbenoted,however,thatADOcurrentlydoesn'tsupportallofDAO'sfunctionality.ADOmostlyincludesRDO-stylefunctionalitytointeractwithOLEDBdatasources,plusremotingandDtechnology.
Ingeneral,it'sprobablytooearlyintheevolutionofADOtomigratemostDAOapplications(exceptpossiblyonesusingODBCDirect)toADOrightnow,sinceADOdoesn'tcurrentlysupportdatadefinition(DDL),users,groups,andsoforth.IfyouuseDAOonlyforclient-serverapplicationsanddon'trelyontheJetdatabaseengineoruseDDL,however,thenyoucanprobablymigratetoADOnow.Eventually,MicrosoftwillprovideanADODDLcomponenttoaidinDAO-to-ADOmigrationandprovidegenericDDLsupportforOLEDBproviders.1<script type="text/javascript"><!--google_ad_client = "pub-2947489232296736";/* 728x15, 创建于 08-4-23MSDN */google_ad_slot = "3624277373";google_ad_width = 728;google_ad_height = 15;//--></script><script type="text/javascript"src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>
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