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I have many questions about how to make relationships N:M in CoreData.

If I have two entities A and B and have a relationship N:M in the entity relationship model has to generate a new table C that will contain the unique id of tables A and B.

Example for the entity relationship:

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Now in the database model:

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Considering the previous example as would be done by core data?

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Or:

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The truth is I'm really lost with that of relations in Core Data, any help will be welcome.

Sorry for my English but not very good.

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对此的答案是，如果您要存储附加信息，即使在 Core Data 中也必须使用“连接表”。您不必跟踪外键，因为这已包含在关系中。

通常，标准数据库“连接表”具有难看的名称，例如“tableA_tableB”。您应该努力找到一个合适的名称以使概念清晰。例如：

Car <<--->> Person
变成
Car <--->> Rental <<---> Person

现在在实体租赁中，您可以添加更多信息，例如时间。因此，例如，如果您想查找在某个日期之前租车的所有人（在 Rental 实体中存储为 NSDate），您的谓词将是这样的：

 [NSPredicate predicateWithFormat:@"ANY rentals.time < %@", cutoffTime]
于 2013-10-17T15:31:51.860 回答