iOS iPhone 获取一对多实体
基本上我有一个包含食物的实体和另一个包含酒的实体。每道菜都有推荐的酒。我需要能够选择一道菜并查看该菜品附带的葡萄酒推荐。不同的菜肴可以推荐相同的酒。
通常在 SQL 中我会创建一个链接表来实现这一点，但我在这里有点困惑，有人可以帮忙吗？
Basically I have an entity that contains food dishes and another that contains wine. Each dish has wine recommendations. I need to be able to select a dish and see the wine recommendations that come with that dish. Different dishes can have the same wine recommended for it.
Normally in SQL I would create a link table to achieve this but I am a bit stumped here, can anyone help?
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核心数据在幕后为您处理“对多”关系的细节，您不需要创建中间表。
打开核心数据 .xcdatamodel 文件，选择
Food实体，然后单击添加关系。将关系命名为wines。使其目标实体成为Wine实体。打开数据模型检查器(option-cmd-3) 并选择对多关系。现在选择
Wine实体。创建一个名为foods的关系。在数据模型检查器中将关系的Desination设置为Food实体，它的逆关系是wines并将其设置为也是一个对多关系。现在，
Food的每个实例可以有许多Wine，而Wine的每个实例可以有许多Food。Core Data handles the details of "to-many" relationships under the hood for you, you don't need to make intermediary tables.
Open your Core Data .xcdatamodel file, select the
FoodEntity, and clickAdd Relationship. Name the relationshipwines. Make its destination entity theWineentity. Open theData Model Inspector(option-cmd-3) and selectTo-Many Relationship.Now select the
Wineentity. Create a relationship calledfoods. In theData Model Inspectormake the relationship'sDesinationtheFoodentity, it's inverse relationship iswinesand set it to be aTo-Many Relationshipas well.Now each instance of
Foodcan have manyWines and each instance ofWinecan have manyFoods.如果您使用 Core Data，那么您可以简单地在数据库中创建一个 Wine 表，并使用它的主键作为 food-dishs 表中的外键。这个设计中什么不起作用？
If you are using Core Data, then you can simply create a Wine table in the database and use it's primary key as the foreign-key in the food-dishes table. What is not working in this design?