在NSManagedObjectModel中添加关系以编程方式创建NSEntityDescription [英] Adding relationships in NSManagedObjectModel to programmatically created NSEntityDescription

问题描述

当你写一个使用CoreData的静态库有一个很大的麻烦，包括一个正常的.xdatamodeld文件到项目中，因为你根本不能将其编译版本（.momd）链接到二进制文件，所以最好创建整个 NSManagedObjectModel 在代码中这样：

When you write a static library which uses CoreData there's a big mess including a normal .xdatamodeld file into the project because you simply cannot just link its compiled version (.momd) into your binary, so it's better to create the whole NSManagedObjectModel in the code like this:

NSAttributeDescription *dateAttribute = NSAttributeDescription.new;

dateAttribute.name = @"timestamp";
dateAttribute.attributeType = NSDoubleAttributeType;
dateAttribute.optional = NO;
dateAttribute.indexed = YES;

NSAttributeDescription *payloadAttribute = NSAttributeDescription.new;

payloadAttribute.name = @"payload";
payloadAttribute.attributeType = NSBinaryDataAttributeType;
payloadAttribute.optional = NO;
payloadAttribute.indexed = NO;

NSEntityDescription *entry = NSEntityDescription.new;

entry.name = entry.managedObjectClassName = NSStringFromClass(MyCustomEntry.class);
entry.properties = @[dateAttribute, payloadAttribute];

NSManagedObjectModel *mom = NSManagedObjectModel.new;

mom.entities = @[entry];

一切都只是完美....

And everything is just perfect....

但是！等等，如果我在 NSManagedObjectModel 中有多个实体，并且它们是相关的（一对多，反转等等），我将如何在世界上连接他们

But! Wait, if I have more than one entity in my NSManagedObjectModel and they are related (to-many, inversed, and so on), how in the world I gonna connect them in the code, like in example above, without that nice Xcode editor, where you make relationships with several mouse clicks?

示例

想象一下，我们有一个类MyCustomElement，它和MyCustomEntry中的代码几乎相同。现在，这里是他们的接口如何如果我使用Xcode生成实体如何出现：

Imagine, we have a class MyCustomElement, which is almost the same as in MyCustomEntry from the code above. Now, here're their interfaces how they would appear if I used Xcode generation for entities:

@interface MyCustomEntry : NSManagedObject

@property (nonatomic, retain) NSNumber *timestamp;
@property (nonatomic, retain) NSData *payload;
@property (nonatomic, retain) MyCustomElement *element;

@end

@interface MyCustomElement : NSManagedObject

@property (nonatomic, retain) NSNumber * timestamp;
@property (nonatomic, retain) NSString * identifier;
@property (nonatomic, retain) NSSet *entries;

@end

@interface MyCustomElement (CoreDataGeneratedAccessors)

- (void)addEntriesObject:(MyCustomEntry *)value;
- (void)removeEntriesObject:(MyCustomEntry *)value;
- (void)addEntries:(NSSet *)values;
- (void)removeEntries:(NSSet *)values;

@end

我需要为他们创建什么NSRelationshipDescription， init？？

What NSRelationshipDescription I need to create for them and how to init it?

推荐答案

关系由 NSRelationshipDescription 对象描述。以下代码为具有关系的MyCustomEntry，MyCustomElement创建两个实体描述

Relationships are described by NSRelationshipDescription objects. The following code creates two entity descriptions for "MyCustomEntry", "MyCustomElement" with relationships

• $ c>（MyCustomElement - > MyCustomEntry，to-many），


• 元素（MyCustomEntry - > MyCustomElement，to-one ），条目的反向。

• entries (MyCustomElement --> MyCustomEntry, to-many),
• element (MyCustomEntry --> MyCustomElement, to-one), inverse of entries.

两个实体只有一个字符串属性标识符（以保存一些代码行）。

Both entities have only a string attribute "identifier" (to save some lines of code).

Objective-c：

NSEntityDescription *entry = [[NSEntityDescription alloc] init];
[entry setName:@"MyCustomEntry"];
[entry setManagedObjectClassName:@"MyCustomEntry"];

NSAttributeDescription *entryIdAttribute = [[NSAttributeDescription alloc] init];
entryIdAttribute.name = @"identifier";
entryIdAttribute.attributeType = NSStringAttributeType;

NSEntityDescription *element = [[NSEntityDescription alloc] init];
[element setName:@"MyCustomElement"];
[element setManagedObjectClassName:@"MyCustomElement"];

NSAttributeDescription *elementIdAttribute = [[NSAttributeDescription alloc] init];
elementIdAttribute.name = @"identifier";
elementIdAttribute.attributeType = NSStringAttributeType;

// To-many relationship from "Element" to "Entry":
NSRelationshipDescription *entriesRelation = [[NSRelationshipDescription alloc] init];

// To-one relationship from "Entry" to "Element":
NSRelationshipDescription *elementRelation = [[NSRelationshipDescription alloc] init];

[entriesRelation setName:@"entries"];
[entriesRelation setDestinationEntity:entry];
[entriesRelation setMinCount:0];
[entriesRelation setMaxCount:0]; // max = 0 for to-many relationship
[entriesRelation setDeleteRule:NSCascadeDeleteRule];
[entriesRelation setInverseRelationship:elementRelation];

[elementRelation setName:@"element"];
[elementRelation setDestinationEntity:element];
[elementRelation setMinCount:0];
[elementRelation setMaxCount:1]; // max = 1 for to-one relationship
[elementRelation setDeleteRule:NSNullifyDeleteRule];
[elementRelation setInverseRelationship:entriesRelation];

[entry setProperties:@[entryIdAttribute, elementRelation]];
[element setProperties:@[elementIdAttribute, entriesRelation]];

NSManagedObjectModel *mom = [[NSManagedObjectModel alloc] init];
[mom setEntities:@[entry, element]];

Swift：

let entry = NSEntityDescription ()
entry.name = "MyCustomEntry"
entry.managedObjectClassName = "MyCustomEntry"

let entryIdAttribute = NSAttributeDescription()
entryIdAttribute.name = "identifier";
entryIdAttribute.attributeType = .StringAttributeType;

let element = NSEntityDescription()
element.name = "MyCustomElement"
element.managedObjectClassName = "MyCustomElement"

let elementIdAttribute =  NSAttributeDescription()
elementIdAttribute.name = "identifier"
elementIdAttribute.attributeType = .StringAttributeType

// To-many relationship from "Element" to "Entry":
let entriesRelation = NSRelationshipDescription()

// To-one relationship from "Entry" to "Element":
let elementRelation = NSRelationshipDescription ()

entriesRelation.name = "entries"
entriesRelation.destinationEntity = entry
entriesRelation.minCount = 0
entriesRelation.maxCount = 0  // max = 0 for to-many relationship
entriesRelation.deleteRule = .CascadeDeleteRule
entriesRelation.inverseRelationship = elementRelation

elementRelation.name = "element"
elementRelation.destinationEntity = element
elementRelation.minCount = 0
elementRelation.maxCount = 1 // max = 1 for to-one relationship
elementRelation.deleteRule = .NullifyDeleteRule
elementRelation.inverseRelationship = entriesRelation

entry.properties = [entryIdAttribute, elementRelation]
element.properties = [elementIdAttribute, entriesRelation]

let mom = NSManagedObjectModel()
mom.entities = [entry, element]

我已经测试过这个代码，它似乎工作，所以我希望它对你有用。

I have tested this code and it seems to work, so I hope that it will be useful to you.

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