hierarchical data_ persistence via closure table _ the b^2 brand.pdf

27/6/2015 HierarchicalData:PersistenceviaClosureTable|TheB^2Brand

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HierarchicalData:PersistenceviaClosureTable

NOVEMBER19,2011BYB2BERRY 11COMMENTS

Recently,Ivebeenworkingwithhierarchicaldatausingclosuretables.Theproblemthistechniquesolvesformeispersistinghierarchicalrelationshipsofspecificentitieswithoutanyrestrictiononthesizeofthehierarchyandwhileprovidingasimplewaytoquerythehierarchy.Closuretables,aboveothersolutionslikepathenumeration,maintainreferentialintegrity.

InaseriesofpostsaboutstoringhierarchicaldataImgoingtowalkthroughimplementingasolutionforworkingwithhierarchicaldataatthepersistencelayer,theapplicationlayer,andthepresentationlayer.WellseewhatisnecessarytopersistthehierarchyinSQLServer2008,howwewraptheclosuretablesintheapplication,andhowwebuildhierarchyintheuserinterfacewithMVC3

First,letsdigrightinandlookatwhatsnecessarytosetuptheclosuretable.Intheimagebelowyoullseejustwhatlittleisnecessarytogetgoing.ThetabletitledClosureistheclosuretablewherethemetadataaboutthestructureofthehierarchyisstored.TheParentIDistheforeignkeytotheFamilyMemberIDandtheChildIDistheFamilyMemberIDofoneofthedecedents.ThePathLengthindicateshowfarremovedfromthenodetheChildis.So,ifwearelookingatagrandfather,thenthemselfwouldbePathLength=0,theirchildwouldbePathLength=1,andtheirgrandchildwouldbePathLength=2.

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27/6/2015 HierarchicalData:PersistenceviaClosureTable|TheB^2Brand

http://b2berry.com/2011/11/19/hierarchicaldatapersistenceviaclosuretable/ 2/6

ParentID ChildID PathLength

1 1 0

1 2 1

1 3 1

1 4 2

1 5 1

1 6 2

1 7 2

2 2 0

2 4 1

3 3 0

3 6 1

3 7 1

4 4 0

5 5 0

6 6 0

7 7 0

YoumayhavealsonoticedthattheFamilyMemberstablealsoholdsaParentID.Thismakesthingsconvenient,butisnotcompletelynecessary.TounderstandmoreaboutwhytheParentIDispresent,letslookatthetriggerFamilyMemberClosureTrigger.Everyonescomfortlevelwithdatabasetriggersisdifferentbuttomethisisoneofthoseappropriatecasesforone.Inthiscase,thetriggerisresponsibleforcreatingthemetadataentriesfortheClosuretableeachtimearecordisinsertedintoFamilyMembers(orupdated,deleted,etc).Thisisntabsolutelynecessary,though.Youcoulddefinitelymovethislogicelsewhereanddoawaywiththetriggeraltogether.

Atthispoint,wereallsetupfornewFamilyMemberstobeinsertedintotheFamilyMemberstable.Letstakealookatthedatawhenthesetablesarepopulated.Below,youcanseetheClosureTable(left)andtheFamilyMemberstable.TakeamomenttoobservejustwhattheClosureTableisstoringforus.

12345678910111213141516171819202122232425

Here,wecreatethetriggerwhenanINSERTtakesplaceinFamilyMemberstable.UpdateandDeletearestillnecessarybutleftthemoutforthisdemoCREATETRIGGER[dbo].[FamilyMemberClosureTrigger]ON[dbo].[FamilyMembers]FORINSERTASDECLARE@MemberIDINT;DECLARE@ParentIDINT;GettheFamilyMemberIDofthenewlyinsertedrecordSELECT@MemberID=i.FamilyMemberIDFROMINSERTEDi;GettheIDofthenewrecord'sparentSELECT@ParentID=i.ParentIDFROMINSERTEDi;First,weinserttherecordforthenewlyinsertedFamilyMemberThisisaselfreferencingrecord,meaningtheParentID=ChildIDAndPathLength=0.INSERTINTOClosure(ParentID,ChildID,PathLength)VALUES(@MemberID,@MemberID,0)Next,weinsertmetadataabouthowthisnewfamilymemberisrelatedtotherestofthehierarchy.INSERTINTOClosure(ParentID,ChildID,PathLength)SELECTp.ParentID,c.ChildID,p.PathLength+c.PathLength+1FROMClosurep,ClosurecWHEREp.ChildID=@ParentIdANDc.ChildID=@MemberID

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27/6/2015 HierarchicalData:PersistenceviaClosureTable|TheB^2Brand

http://b2berry.com/2011/11/19/hierarchicaldatapersistenceviaclosuretable/ 3/6Data closuretable,data,hierarchy,SQL

FamilyMemberID ParentID Name

1 0 JohnDoe

2 0 BillyDoe

3 1 MaryDoe

4 2 Bobby

5 1 BobbyDoe

6 3 SammyDoe

7 3 MaeDoe

TheClosureTable,bystoringthismetadataabouttheFamilyMembersenablesustodirectlyquerytherelationshipsinthehierarchyprettyquickly.Thatis,wecanaskquestionslikeWhoareallofthegrandchildrenofJohnDoe

Whichresultsin:

ParentID ChildID PathLength

1 4 2

1 6 2

1 7 2

Asyoucansee,thismakesthingsrelativelysimpleforquerying.Though,therearesomedownsidestothissolution.Wecanseethesizeoftheclosuretablewillgrowexponentiallyfasterthantheentitytable(FamilyMembers).Also,theclosuretableisnotsimpletodebug,thatisifthetablebecomescorrupti.e.failedwrites,etc,thenthetablewillneedtoberebuiltasattemptingtotrackdownthebrokenrelationshipvisuallyisnotimpossiblebutanexerciseintedium.Ontheotherhand,therelationshipsareprettysimplesorebuildingpartorallofthehierarchyisntsobad,especiallyifyoualsoimplementtheParentIDontheentitytableitselfitspartofthecharm.

InthenextpostIwillbewalkingthroughhowtobuildacustomdatastructuretoabstracttheapplicationfromtheclosuretableandworkwiththehierarchythroughouttheapplication.

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SELECT*FROMClosurecWHEREc.ParentID=1ANDPathLength=2

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27/6/2015 HierarchicalData:PersistenceviaClosureTable|TheB^2Brand

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AntoninJanuska(@AntJanus) ReplyAugust3,2012at11:48am

b2berry ReplyAugust3,2012at5:12pm

11ResponsestoHierarchicalData:PersistenceviaClosureTable

Youvegotaprettyamazinganswerthere.Iwonderifyoucouldhelpmewithmydilemma:http://stackoverflow.com/questions/11790108/whattablestructuretousefornesteddata

Itsbasicallyahierarchicalstructureliketheoneyoudescribebutabitmorecomplex.Inyouranalogyofthechildren/parents,letssayIcanmovechildrenaround.

LetssaythatSammyDoe(canmagically)becomeolderthanMayDoeandthusbethefirstgreatgrandchild,howwouldyouhandlethat?Icanimagineaddingapositioncolumntogetthatoutoftheway.

Okaybuthowwouldyou,forexample,callupthe2ndgreatgrandchildofthe1stgrandchildofthe2ndchildofthegrandfather?orhowaboutonlythegrandchildrenofBillyDoewhereonlyMaryDoeistheparent?

Idgreatlyappreciateyourhelp

GreatquestionAntonin,thatdoessoundlikesomeextracomplexity.Haveyouconsideredreorganizingthetree?RecentlyIveusedclosuretablesinanarchitecturewhichallnodesinthetreeareabletoberearrangedandalsoexistinmultipleplacessimultaneously.Thatis,theUIallowsforausertodragsomethinginthehierarchytoacompletelynewlocationinthehierarchy.

Imgoingtoproposetwowaystosolvethis,thefirstwiththeexistingschemaIvepresentedabove,andthesecondsolutionaddsalayerofabstraction.

First:Youcouldhandlethisbyrearrangingtherelationshipsofthenodes.So,ifyoumoveSammyDoeaboveMayDoethenIdgotoworkintheclosuretablechangingparentchildrelationshipsofthetwoinordertoswitchtheirpositions.Ifyouthinkaboutitlikealinkedlist,thelogicissimilarwhereyoullwanttostoretheparentofbothMayDoeandSammyDoesoyoucanmakechangestotherelationshipswithoutloosingalltherelationshipsunderthesenodes,thatisallthechildrenofthesenodesyoureshufflingaround.

Second,andIthinkabettersolutiongivenyourconstraintsistocreateatablewhichabstractbetweenthefamilymembersandthetreeitself.CreateatablecalledFamilyMemberNodeswhichsimplyaliasestheFamilyMemberIDtoapositioninthetree.Then,yourclosuretablewouldbebeconstructedbasedoffyourFamillyMemberNodestable,nottheFamilyMembertableoritskeys.Then,whenyouwanttoswaptwofamilymembersinthetreeyoumakethechangeattheFamilyMemberNodestableandyoudontneedtotouchthestructureofthetreeitself.

Incidentally,itssolutiontwowhichalsoallowsforFamilyMemberstoexistinmultipleplaces(Whichdoesntmakesenseforfamilymemberswhataweirdthought!)butwouldmakesenseforother

27/6/2015 HierarchicalData:PersistenceviaClosureTable|TheB^2Brand

http://b2berry.com/2011/11/19/hierarchicaldatapersistenceviaclosuretable/ 5/6

AntoninJanuska(@AntJanus) August3,2012at7:40pm

b2berry August3,2012at10:04pm

AntoninJanuska(@AntJanus) ReplyAugust3,2012at10:40pm

b2berry ReplyAugust4,2012at1:45pm

http://tinyurl.com/satgbiggs06390 ReplyFebruary4,2013at10:10pm

memberswhataweirdthought!)butwouldmakesenseforothercaseslikeashoppingcart,etc.

Anywaylongwindedanswerbutdoesanyofthishelp?

Imthinkingofdoingthesame.HavethatdragndropUIthatallowschangingofthenodes.Butmymainproblemistryingtofigureoutawaytocallupthosespecificnodes(1stoftoplevel,2ndofmid,5thoflast).

ToseeifIunderstandthisright,youreproposing:

*changingaroundtheclosuretablewitheachupdate/changebyupdatingthechild/parentdeclarations.ThisseemsabitcomplexbutIdontseeawayaroundit.*ImnotentirelysureIunderstandyoursecondexplanation.Imtryingtowrapmyheadaroundit.Itwouldbeaninbetweentablewhichwouldholdposition(firstchild,secondchild,firstgrandpa),andtheidwhichcorrespondstotheidinthefamilytable.

Iguessbyimplementingbothofthese,icouldmakeitwork.HavetheNodestabledeclareparent/childrelationships,theinbetweentabledeclareposition,andthemaintablehavetheactualdata.WheneverIwanttochangethepositionofthenode,Icanusetheinbetween.IfIwanttochangetheparent/childrelationship,IllhavetousetheNodestableandupdateitaswellastheinbetweentable.Thanksforyourhelp.Imstillnot100%sureofhowtodothisallefficientlyandifImmissingsomething. especiallyqueryingthisdata.

Thereisasimplersolutionherethanwhatscomingacrosshere,Ithink.Iwillattempttowriteanewpostortwothisweekendwiththedifferentapproachtotheclosuretablewhichshouldmakemysecondsuggestionmoreclear.IvebeenmeaningtorevisitthistopicwithwhatIvelearnedanyway.

Youreawesome.Thankyouforallyourhelp!Illdefinitelybefollowingyourblog

IfoundthisanincrediblyintricatematterbutIfinditextremelyuseful/necessarytowhatImtryingtobuild Itseemslikenooneonredditorstackoverflowhasanygoodideasotherthanbreakingthisdowntoindividualtablesforeachlevel,ditchingthisaltogetherbecauseSQLcantdothis(itobviouslycan),andsomeotherstuff.

Hereyougo!Hopefullythisbetterconveysthe2ndoptionIdescribedabove.Itsnota100%getoutofjailfreecard,butIhadalotofsuccessmodelingwiththisapproachoverthemorevanillaapproachintheabovepost

http://b2berry.com/2012/08/04/convertingtheclosuretablefromaweakentity/

IhavesomemorepostsImaybecrankingoutthisweekendrelativelyminoradditionstotheconcept.

27/6/2015 HierarchicalData:PersistenceviaClosureTable|TheB^2Brand

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1.HierarchicalData:ApplyingDataStructuresTheB^2BrandNovember20,2011[]mypreviouspostIwalkedthroughpersistinghierarchicaldatausingclosuretables.Whileclosuretablesarea[]

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