我在项目中使用了一般的CoreData查询方法。
func query(table: String, searchPredicate: NSPredicate) -> [AnyObject]
{
let context = app.managedObjectContext
let fetchRequest = NSFetchRequest(entityName: table)
fetchRequest.predicate = searchPredicate
let results = try! context.fetch(fetchRequest)
return results
}
在Swift 3中,这不起作用。我在Apple的网站上找到了这个:
func findAnimals()
{
let request: NSFetchRequest<Animal> = Animal.fetchRequest
do
{
let searchResults = try context.fetch(request)
... use(searchResults) ...
}
catch
{
print("Error with request: \(error)")
}
}
使用Apple示例,我如何将Animal作为参数传递给方法,以使findAnimals更通用?
答案 0 :(得分:4)
我还没试过这个,但我觉得这样的事情会起作用......
func findCoreDataObjects<T: NSManagedObject>() -> [T] {
let request = T.fetchRequest
do
{
let searchResults = try context.fetch(request)
... use(searchResults) ...
}
catch
{
print("Error with request: \(error)")
}
}
你必须使整个函数通用,所以你必须告诉它在调用时它是什么类型。
someObject.findCoreDataObjects<Animal>()
我认为应该做的工作。虽然我自己对仿制药不熟悉,但并不完全确定:D
答案 1 :(得分:1)
这个怎么样。
func query<T: NSManagedObject>(table: String, searchPredicate: NSPredicate) -> [T] {
let context = app.managedObjectContext
let fetchRequest: NSFetchRequest<T> = NSFetchRequest(entityName: table)
fetchRequest.predicate = searchPredicate
let results = try! context.fetch(fetchRequest)
return results
}
答案 2 :(得分:0)
以下是可能有助于某人的最终结果:
import Foundation
import Cocoa
func addRecord<T: NSManagedObject>(_ type : T.Type) -> T
{
let entityName = T.description()
let context = app.managedObjectContext
let entity = NSEntityDescription.entity(forEntityName: entityName, in: context)
let record = T(entity: entity!, insertInto: context)
return record
}
func recordsInTable<T: NSManagedObject>(_ type : T.Type) -> Int
{
let recs = allRecords(T.self)
return recs.count
}
func allRecords<T: NSManagedObject>(_ type : T.Type, sort: NSSortDescriptor? = nil) -> [T]
{
let context = app.managedObjectContext
let request = T.fetchRequest()
do
{
let results = try context.fetch(request)
return results as! [T]
}
catch
{
print("Error with request: \(error)")
return []
}
}
func query<T: NSManagedObject>(_ type : T.Type, search: NSPredicate?, sort: NSSortDescriptor? = nil, multiSort: [NSSortDescriptor]? = nil) -> [T]
{
let context = app.managedObjectContext
let request = T.fetchRequest()
if let predicate = search
{
request.predicate = predicate
}
if let sortDescriptors = multiSort
{
request.sortDescriptors = sortDescriptors
}
else if let sortDescriptor = sort
{
request.sortDescriptors = [sortDescriptor]
}
do
{
let results = try context.fetch(request)
return results as! [T]
}
catch
{
print("Error with request: \(error)")
return []
}
}
func deleteRecord(_ object: NSManagedObject)
{
let context = app.managedObjectContext
context.delete(object)
}
func deleteRecords<T: NSManagedObject>(_ type : T.Type, search: NSPredicate? = nil)
{
let context = app.managedObjectContext
let results = query(T.self, search: search)
for record in results
{
context.delete(record)
}
}
func saveDatabase()
{
let context = app.managedObjectContext
do
{
try context.save()
}
catch
{
print("Error saving database: \(error)")
}
}
用以下方式调用:
let name = "John Appleseed"
let newContact = addRecord(Contact.self)
newContact.contactNo = 1
newContact.contactName = name
let contacts = query(Contact.self, search: NSPredicate(format: "contactName == %@", name))
for contact in contacts
{
print ("Contact name = \(contact.contactName), no = \(contact.contactNo)")
}
deleteRecords(Contact.self, search: NSPredicate(format: "contactName == %@", name))
recs = recordsInTable(Contact.self)
print ("Contacts table has \(recs) records")
saveDatabase()
答案 3 :(得分:0)
我在项目中使用这种方式:
static func retrieveRecords<T: NSManagedObject>(table: String, sortDescriptorKey: NSSortDescriptor? = nil) -> [T] {
do {
let fetchRequest: NSFetchRequest<T> = NSFetchRequest(entityName: table)
fetchRequest.sortDescriptors = [sortDescriptorKey!]
let results = try context.fetch(fetchRequest)
print("\(results)")
return results
} catch let error {
print("Could not fetch \(error.localizedDescription)")
return []
}
}
并称之为:
personen = retrieveRecords(table: "Person", sortDescriptorKey: NSSortDescriptor(key: #keyPath(Person.nachname), ascending: true, selector: #selector(NSString.localizedCompare)))