中英文双语计算机专业毕业设计外文文献翻译成品：Django框架介绍（最新）.docx

中英文双语计算机专业毕业设计外文文献翻译成品：Django框架介绍（最新）.docx

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外文标题：

IntroductiontotheDjangoFramework

外文作者：

DanielRubio

文献出处:

DanielRubio.IntroductiontotheDjangoFramework[M].BeginningDjango.2017:

1-29

英文8701单词，40127字符，中文12987汉字。

IntroductiontotheDjangoFramework

DanielRubio

TheDjangoframeworkstartedin2003,asaprojectdonebyAdrianHolovatyandSimonWillisonattheJournal-WorldnewspaperinLawrence,Kansas,intheUnitedStates.In2005,HolovatyandWillisonreleasedthefirstpublicversionoftheframework,namingitaftertheBelgian-FrenchguitaristDjangoReinhardt.

Fastforwardto2017–theDjangoframeworknowoperatesundertheguidanceoftheDjangoSoftwareFoundation（DSF）,theframeworkcorehasover1000contributorswithmorethan15releaseversions,andthereareover3000packagesspecificallydesignedtoworkwiththeDjangoframework.1

TheDjangoframeworkhasremainedtruetoitsoriginsasaModel-View-Controller（MVC）server-sideframeworkdesignedtooperatewithrelationaldatabases.Nevertheless,Djangohasstayeduptodatewithmostwebdevelopmenttendencies–viathird-partypackages–tooperatealongsidetechnologieslikenon-relationaldatabases（NoSQL）,real-timeInternetcommunication,andmodernJavaScriptpractices.Allthistothepoint,theDjangoframeworkisnowthewebdevelopmentframeworkofchoiceforawidearrayoforganizations,includingthephotosharingsitesInstagram2andPinterest3;thePublicBroadcastingSystem（PBS）4;intheUnitedStates,NationalGeographic5;andwiththehelpofthisbook,yourorganization!

Inthischapteryou’lllearnabouttheDjangoframeworkdesignprinciples,whicharekeytounderstandingtheday-to-dayaspectsofworkingwiththeDjangoframework.Next,you’lllearnhowtoinstallDjangoinvariousways:

asatar.gzfile,withpip,

usinggit,andwithvirtualenv.

OnceyouinstalltheDjangoframework,you’lllearnhowtostartaDjangoprojectandhowtosetitupwitharelationaldatabase.Next,you’lllearnaboutthecorebuildingblocksintheDjangoframework–urls,templates,andapps–andhowtheyworkwithoneanothertosetupcontent.Finally,you’lllearnhowtosetuptheDjangoadminsite,whichisaweb-basedinterfacedesignedtoaccesstherelationaldatabaseconnectedtoaDjangoproject.

DjangoFrameworkDesignPrinciples

Ifyouworklongenoughinwebdevelopment,you’lleventuallycometotheconclusionthatyoucanproducethesameresultswithjustaboutanywebframeworkandprogramminglanguage.Butwhileyoucan,infact,produceidenticalresults,whatwillvarydrasticallyisthetimeyouspendcreatingasolution:

thetimecreatingaprototype,thetimeaddingnewfeatures,thetimedoingtesting,thetimedoingdebugging,andthetimedeployingtoscale,amongotherthings.

Inthissense,theDjangoframeworkusesasetofdesignprinciplesthatproducesoneofthemostproductivewebdevelopmentprocessescomparedtomanyotherwebframeworks.Note,I’mnotsayingDjangoisasilverbullet（e.g.,thebestatprototyping,themostscalable）;I’msayingthatattheendoftheday,theDjangoframeworkincorporatesasetofdesignprinciplesandtrade-offsthatmakeitoneofthemostproductiveframeworksforbuildingthefeaturesneededbymostmediumtolargewebapplications.Now,whileyoumightthinkI’mbiased–afterallI’mwritinganentirebookaboutthetopic–I’lllayoutthesedesignprinciplesfirst,soyoucangainabetterunderstandingofwhatgivestheDjangoframeworkthisedge.

Don’tRepeatYourself（DRY）Principle

Repetitionmightbegoodtoemphasizeapoint,butwhenitcomestowebdevelopment,itjustleadstoadditionalandtime-consumingwork.Infact,theverynatureofwebdevelopment,whichoperatesacrossmultipletiersinteractingwithoneanother（e.g.,HTMLtemplates,businesslogicmethods,anddatabases）,lendsitselftorepetition.

TheDjangoframeworkreallytriestoforceyounottorepeatyourself,solet’sseehowDjangoenforcesnotrepeatingyourselfandwhythisisagoodthing.Let’ssayyouwanttobuildacoffeehouseapplicationtopublishinformationaboutstoresandalsohaveacontactformforcustomers.Thefirstthingyou’llneedtodoisdeterminewhatkindofinformationisrequiredforstoresandthecontactform.Figure1-1illustratesa

mock-upoftwoDjangomodelsforeachoftheseentities.

Figure1-1.Djangomodelsforstoreandcontactentities

NoticehowtheDjangomodelsinFigure1-1eachhavedifferentfieldnamesandadatatypetorestrictvalues.Forexample,thestatementname=models.CharField（max_length=30）tellsDjangoastorenameshouldhaveamaximumof30characters,whilethestatementemail=models.EmailField（）tellsDjangothecontactentityshouldcontainavalidemailvalue.Ifthecoffeehouseislikemostwebapplications,you’llgenerallyendupdoingthefollowingforthestoreandcontactentities:

•Createrelationaldatabasetablestosaveentityinformation.

•Createbusinesslogictoensuretheentitiescomplywithrequirements.

•CreateHTMLformstoallowdatatobesubmittedfortheentities.

•Createaninterfacetoallowadministrativeuserstoaccessentitiesinthedatabase.

•CreateRESTservicestoexposeentitiesforamobileappversion.

Thecruxofdoingthislasttasklistisyouhavethepotentialofrepeatingdozensofsimilarpiecesofinformation（e.g.,names,valuelimits）indatabasedefinitionlanguage（DDL）,HTMLforms,businessvalidationlogic,andURLs,amongotherthings–processthat’snotonlytimeconsuming,butalsoerrorprone.Wouldn’titbeeasierthatbasedonastatementlikemodels.CharField（max_length=30）youcouldgenerateanHTMLforminput,aDDLstatement,andautomaticallyvalidateinformationtoonlycontain30characters?

ThisisexactlywhatDjango’sDRYdesignprincipledoes.Figure1-2illustratesthesameDjangomodelsfromFigure1-1andthevariousconstructsyoucangeneratefromthesamemodelswithouttheneedtorepeatyourself.

Figure1-2.DjangomodelscreateseparateconstructsbasedonDRYprinciple

AsyoucanseeinFigure1-2,theentitiesthatrepresentDjangomodelsarecapableofgeneratingHTMLformstopresenttothepublic,anadministrativeinterfacetomanagetheentities,validationlogictoenforceentityvalues,aswellastheDDLtogeneratedatabasetablesrepresentingtheentities.

Whileit’salittleprematuretodiscusstheactualtechniquestogeneratesuchconstructsfromDjangomodels,needlesstosayit’smuchsimplerthankeepingtrackofmultiplereferencesofthesamething（e.g.,name,email）inHTMLforms,DDL,validationlogic,andotherlocations.

Inthissense,Djangoreallyhelpsyoudefinethingsinasingleplaceandnothavetorepeatthemelsewhere.Notethatit’salwayspossibletorepeatyourselftoobtaincustombehaviors,butbydefault,DjangoenforcesDRYprinciplesinnearlyeverythingyoudowithit.

ExplicitIsBetterThanImplicit

Python,theprogramminglanguageusedbyDjango,hasamantra-likestatementcalled“TheZenofPython”definedaspartofthelanguage’sPythonEnhancement

Proposals（PEP）,specificallyPEP20.6OneofthestatementsinPEP20states“Explicitisbetterthanimplicit”andwithDjangobeingbasedonPython,thisprincipleisalsotakentoheart.

Beingexplicitleadstowebapplicationsthatareeasilyunderstoodandmaintainedbyagreaternumberofpeople.Addingnewfeaturesorunderstandingthelogicbehindawebapplicationcanbehardenoughforsomeonethatdidn’twriteitoriginally,butifyoutossintothemixconstructsthathaveimplicitbehaviors,usersonlyfacegreaterfrustrationtryingtofigureoutwhat’sbeingdoneimplicitly.Explicitdoesrequirealittlemoreworktyping,butit’swellworthitwhenyoucompareittothepotentialeffortyoucanfacetryingtodebugorsolveaproblem.

Let’stakeaquicklookatDjango’sexplicitnessinacommonwebdevelopmentconstructusedacrossdifferentMVCframeworks:

aviewmethod.AviewmethodactsastheC（ontroller）inanMVCframework,chargedwithhandlingincomingrequests,applyingbusinesslogic,andthenroutingrequestswithanappropriateresponse.

Togetabetterfeelforthisexplicitness,I’llpresentaDjangoviewmethodandanequivalentRubyonRailsviewmethodthatperformsthesamelogicoffetchingastorebyagivenidandroutingtheresponsetoatemplate.ThefollowingsnippetistheRubyonRailsversion;notethelineswith#thatarecommentsandindicatewhat’shappening.

classStoresController

#Automaticaccesstoparams,arubyhashwithrequestparametersandviewparameters@store=Store.find（params[:

id]）

#Instancevariableslike@storeareautomaticallypassedontoviewtemplate

#Automaticallyusestemplateviews/stores/show.html.erbend

end

Althoughverysuccinct,noticealltheimplicitbehaviorsurroundingtheprocesstoaccessdata,passdatatoatemplate,andassignatemplate.ThefollowingsnippetisanequivalentDjangoviewmethod.

#Explicitrequestvariablecontainsrequestparameters

#Otherviewparametersmustbeexplicitlypassedtoviewsdefdetail（request,store_id）:

store=Store.objects.get（id=store_id）

#Instancevariablesmustbeexplicitlypassedontoaviewtemplate#Explicittemplatemustbeassigned

returnrender（request,'stores/detail.html',{'store':

store}）

Noticeinthislastsnippetthere’snoguessingwhereinputparameterscomefrom,they’reexplicitlydeclar