Relationships
Relationships link entities. Using relationships in the managed object model introduces a powerful means to connect logical areas of data represented by entities. Using relationships can significantly reduce the capacity requirements of a database. Instead of duplicating the same data in multiple entities, a relationship can be put in place as a pointer to a piece of data so it only needs to be stored once. Although de-duplication is one advantage, the true power of relationships is their ability to allow connections between complex data types.
Consider the existing Item and Unit entities found in Grocery Dude’s model. Instances of the Item entity will represent things you can put on a shopping list, such as the following:
Chocolate ...
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