当你编写一个使用CoreData的静态库时，包含一个普通的.xdatamodeld文件会进入项目，因为你不能只将它的编译版本（.momd）链接到你的二进制文件中，所以最好创建整个{ {1}}代码如下：
NSManagedObjectModel一切都很完美......
但是！等等，如果我的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];
中有多个实体并且它们是相关的（多对齐，反向等等），那么在世界上我将如何在代码中连接它们，如上例所示，那个很好的Xcode编辑器，你可以通过几次鼠标点击建立关系吗？
示例
想象一下，我们有一个MyCustomElement类，它与上面代码中的MyCustomEntry几乎相同。现在，这是他们的界面，如果我使用Xcode生成实体，它们将如何出现：
NSManagedObjectModel我需要为他们创建什么样的NSRelationshipDescription以及如何启动它？
答案 0 :(得分：18)
关系由NSRelationshipDescription个对象描述。以下代码为“MyCustomEntry”创建了两个实体描述，“MyCustomElement”创建了关系
entries（MyCustomElement - ＆gt; MyCustomEntry，to-many），element（MyCustomEntry - ＆gt; MyCustomElement，to-one），与entries相反。两个实体都只有一个字符串属性“identifier”（用于保存一些代码行）。
<强>目标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 （现已更新为Swift 3/4）：
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]
我已经测试了这段代码，它似乎有效，所以我希望它对你有用。