core data 学习笔记

学习路线: 

Core Data Tutorial for iOS

Core Data Utility Tutorial

Core Data Programming Guid 

code: CoreDataBooks

Core Data Model Versioning and Data Migration Programming Guide

Atomic Store Programming Topics

Incremental Store Programming Guide

Xcode Tools for Core Data

Xcode Mapping Tool for Core Data

Cocoa Bindings Programming Topics

???: 实现SELECT 部分字段效果用:

 NSExpression 的 expressionForKeyPath:

和 NSExpressionDescription ?

[fetchRequest setPropertiesToFetch:[NSArray arrayWithObject:expressionDescription]];

context -‐-‐-‐> coordinator -‐-‐-‐> model

1. Managed Object Model is an object representation of a schema that describes your database

is a collection of entity description objects (instances of NSEntityDescription).

2. A persistent object store represents an external store (file) of persisted data

When you fetch records, Core Data retrieves results from all of them (unless you specify which store you’re interested in).

3. A managed object is an object representation of a record in a table in a database

A managed object is associated with an entity description (an instance of NSEntityDescription) that provides metadata about the object (including the name of the entity that the object represents and the names of its attributes and relationships)

4. The managed object context  manage a collection of managed objects. These objects form a group of related model objects that represent an internally consistent view of one or more persistent stores.

5. 一个Entity 可以 用于存放不同的store..

You specify the store for an object using the NSManagedObjectContext method, assignObject:toPersistentStore:.

Transient properties are properties that you define as part of the model, but which are not saved to the persistent store as part of an entity instance's data.

an attribute is optional—that is, it is not required to have a value

Fetched properties represent weak, one‐way relationships

可以 cross stores.

Relationships represent to-many relationship

不能 cross stores.

Faulting : a managed object may be a “fault”—an object whose property values have not yet been loaded from the external store

When you fetch a managed object, Core Data does not automatically fetch data for other objects to which it has relationships