![]() ![]() Country+CoreDataProperties.swift is more complex, because Xcode also generated some methods for us to use. Candy+CoreDataProperties.swift will be pretty much exactly what you expect, although notice how origin is now a Country. Select both Candy and Country and set their Codegen to Manual/None, then go to the Editor menu and choose Create NSManagedObject Subclass to create code for both our entities – remember to save them in the CoreDataProject group and folder.Īs we chose two entities, Xcode will generate four Swift files for us. Remember to press Cmd+S to force Xcode to save your changes. That completes our entities, the next step is to take a look at the code Xcode generates for us. Call the relationship “origin”, change its destination to “Country”, then set its inverse to “candy” so Core Data understands the link goes both ways. ![]() Now select Candy, and add another relationship there.Call the relationship “candy”, change its destination to Candy, then over in the data model inspector change Type to To Many. ![]() With Country selected, press + under the Relationships table.Tip: Don’t worry if you’ve forgotten how to add constraints: select the Country entity, go to the View menu and choose Inspectors > Data Model, click the + button under Constraints, and rename the example to “shortName”.īefore we’re done with this data model, we need to tell Core Data there’s a one-to-many relationship between Candy and Country: Although some types of candy have the same name – see “Smarties” in the US and the UK – countries are definitely unique, so please add a constraint for “shortName”. So, open your data model and add two entities: Candy, with a string attribute called “name”, and Country, with string attributes called “fullName” and “shortName”. In our example, this would mean that one type of candy had been introduced simultaneously in many countries, and each country can make many types of candy.Īll of those are used at different times, but in our candy example the many to one relationship makes the most sense – each type of candy was invented in a single country, but each country can have invented many types of candy. A many to many relationship means that many objects in an entity link to many objects in another entity.In our example, this would mean that each type of candy has one country of origin, and that each country can make many types of candy. A many to one relationship means that many objects in an entity link to one object in another entity.In our example, this would mean that one type of candy could have been introduced simultaneously in many countries, but that each country still could only make one type of candy. A one to many relationship means that one object in an entity links to many objects in another entity.In our example, this would mean that each type of candy has one country of origin, and each country could make only one type of candy. A one to one relationship means that one object in an entity links to exactly one object in another entity.To demonstrate this, we’re going to build two Core Data entities: one to track candy bars, and one to track countries where those bars come from. ![]() However, this is one area where Core Data shows its age a little: to get relationships to work well we need to make a custom NSManagedObject subclass that providers wrappers that are more friendly to SwiftUI. Core Data allows us to link entities together using relationships, and when we use Core Data sends all that data back to us for use. ![]()
0 Comments
Leave a Reply. |