Core Data Multi-Table Association

1. Concept Introduction

When there are complex data relationships in coredata, a table is difficult to meet the requirements, and you need to understand the use of CoreData multi-table associations.

The relationship between a curriculum and a chapter table: a course is one-to-many and one-to-one chapters can correspond to a single course; And the relationship between the curriculum and the instructor table: a course can have multiple lecturers, a lecturer can also speak multiple courses, and they are many-to-many relationships.

Tables are linked by this mutually binding relationship.

The following is a code demonstration of the movie and cast tables:

Steps to create:

1> Create the data Model;2> Create Movie,actor table, set foreign key;3> Create Nsmanagedobject subclass; Code implementation:

1 #import "ViewController.h"2 #import<CoreData/CoreData.h>3 #import "Actor.h"4 #import "Movie.h"5 6 7 @interfaceViewcontroller ()8 9 {TenNsmanagedobjectcontext *CTX; One     A } - @end -  the @implementationViewcontroller -  -- (void) Viewdidload { - [Super Viewdidload]; +    -     //1. Path to the application package +     //NSLog (@ "%@", [[NSBundle Mainbundle] resourcepath]); A     atNSString *filepath = [[NSBundle mainbundle] Pathforresource:@"MOVIEINFO.MOMD"Oftype:nil]; -     -     //1. Loading the data Model file -Nsmanagedobjectmodel *managemodel =[[Nsmanagedobjectmodel alloc] Initwithcontentsofurl:[nsurl Fileurlwithpath:filepath]]; -     -     //2. Persistent data store scheduler, specifying how the storage is to be used to operate between the application and the database inNspersistentstorecoordinator *coordinator =[[Nspersistentstorecoordinator alloc] initwithmanagedobjectmodel:managemodel]; -     to     //3. Specify the path to the database +NSString *dbfile = [Nshomedirectory () stringByAppendingPathComponent:@"documents/coredata.db"]; -NSLog (@"%@", dbfile); the     *Nserror *error =Nil; $    Panax Notoginseng     //4. How to add persistent storage (either a database or XML) and open the database -[Coordinator Addpersistentstorewithtype:nssqlitestoretype Configuration:nil Url:[nsurl FileURLWithPath:dbfile] Options:nil error:&ERROR]; the     +     if(Error) { A         theNSLog (@"failed to open database"); +}Else{ -NSLog (@"Open Database succeeded"); $     } $     -     //4. Store data, update data, query the data context -CTX =[[Nsmanagedobjectcontext alloc] init]; the     - [CTX Setpersistentstorecoordinator:coordinator];Wuyi     the     //5. Add Movie Data - [self insertmoviedata]; Wu     -     //6. Query Movie Data About [self querymoviedata]; $     - } -  - //Inserting Data A- (void) insertmoviedata{ +  the     //actor One -Actor *actor1 = [nsentitydescription insertnewobjectforentityforname:@"Action"Inmanagedobjectcontext:ctx]; $Actor1.name =@"Jason Statham"; theActor1.age = @ -; theActor1.height = @1.55; the     the     //actor 2 -Actor *actor2 = [nsentitydescription insertnewobjectforentityforname:@"Action"Inmanagedobjectcontext:ctx]; inActor2.name =@"Tom Cruise"; theActor2.age = @ -; theActor2.height = @1.60; About     the     //Movie One theMovie *m1 = [nsentitydescription insertnewobjectforentityforname:@"Movie"Inmanagedobjectcontext:ctx]; theM1.title =@"Life Express"; +M1.year =[NSDate Date]; -M1.rating = @9.7; theM1.actor =Actor1;Bayi     the     //Movie Two theMovie *m2 = [nsentitydescription insertnewobjectforentityforname:@"Movie"Inmanagedobjectcontext:ctx]; -M2.title =@"Top Gun"; -M2.year =[NSDate Date]; theM2.rating = @9.2; theM2.actor =Actor2; the     the     //movie Three -Movie *m3 = [nsentitydescription insertnewobjectforentityforname:@"Movie"Inmanagedobjectcontext:ctx]; theM3.title =@"Super 7"; theM3.year =[NSDate Date]; theM3.rating = @9.5;94M3.actor =Actor1; the     the     //Add a movie to the context the [CTX INSERTOBJECT:M1];98 [CTX INSERTOBJECT:M2]; About [CTX INSERTOBJECT:M3]; - 101    102     //Save103BOOL issuccess =[CTX Save:nil];104     the     if(issuccess) {106NSLog (@"Insert data Successfully!");107     }108 109 } the 111  the //Querying Data113- (void) querymoviedata{ the     the     //query Stensson starring movie theNsfetchrequest *request = [Nsfetchrequest fetchrequestwithentityname:@"Movie"];117    118     //Set Filter Criteria119Request.predicate = [Nspredicate predicatewithformat:@"actor.name = ' Jason Statham '"]; -    121     //Enquiry122Nsarray *result =[CTX executefetchrequest:request error:nil];123      for(Movie *movieinchresult) {124         theNSLog (@"movie title:%@ Movie Rating:%.2lf", movie.title,[movie.rating Doublevalue]);126     }127  - 129  the}

Core Data Multi-Table Association