CoreData，多对多关系和NSPredicate [英] CoreData, many-to-many relationships and NSPredicate

问题描述

我有一个包含多对多关系的CoreData数据模型。事实证明，NSPredicate不支持多对多关系。从CoreData.pdf：你只能在谓词中的关键字中有一个一对多的元素。

作为一个食谱的例子：许多食谱和许多成分。配方可以具有许多成分，其中盐可以是一种，而盐用于许多配方中。这是一个自然的多对多的关系。

建议的解决方法是什么？

CoreData是一个坏主意，我应该回去到SQLite？

解决方案

我的理解是，你可以使任何多对多关系成为单独的一对多关系

您有：

食谱有很多成分。

成分有很多食谱。 p>

创建一个新的RecipeIngredient实体，以便：

Recipe有许多RecipeIngredients。

成分有很多RecipeIngredients。

RecipeIngredient有一个食谱和一个成分。

I have a CoreData datamodel that includes a many-to-many relationship. As it turns out NSPredicate does not support many-to-many relationships. From CoreData.pdf: "You can only have one to-many element in a keypath in a predicate."

As a Recipe example: Many recipes and many ingredients. A recipe can have many ingredients of which "salt" can be one, while "salt" is used in many recipes. This is a natural many-to-many relationship.

What are suggested work-arounds?
Was CoreData a bad idea and I should go back to SQLite?

解决方案

My understanding is that you can make any many-to-many relationship into separate one-to-many relationships by adding an intermediate entity.

You have:
Recipe has many Ingredients.
Ingredient has many Recipes.

Create a new RecipeIngredient entity such that:
Recipe has many RecipeIngredients.
Ingredients has many RecipeIngredients.
A RecipeIngredient has one Recipe and one Ingredient.

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