我正在尝试创建一个 PFQuery
,其中查询的响应存储在服务器和本地数据存储中。我想创建一个带有约束的查询(query.whereKey()
),它将首先查看响应是否存储在设备上,如果没有,它将查询服务器.
例如,我正在加载帖子列表。该应用程序存储当前用户关注的一组用户。对于存储在设备上的用户发布的帖子,我想从数据存储而不是服务器加载用户详细信息(例如他们的个人资料图片和用户名)。但是,如果该帖子是由未存储在设备上的用户发布的,则它将查询服务器。我只能想象用 2 个不同的查询执行此操作,但我更愿意在一个查询中执行此操作。
最佳答案
我在自己的项目中编写了以下内容,并将其发布,以防有人正在寻找完整的答案。
参数如下:
query
:您要执行查询的PFQuery
。queryBoth
:一个Bool
值,表示如果有从本地数据存储返回的数据,是否要查询 Parse 服务器。true
将同时查询两者,false
仅在本地数据存储未返回任何内容时才查询服务器。toCallUponCompletion
:从服务器、本地数据存储或两者接收到响应时将调用的闭包(函数)。该函数应该接受 PFObjects 数组并且不返回任何内容。该函数的实现将显示在以下函数下方。
功能:
func findObjectsInBackgroundFromLocalDataStoreIfPossible (query: PFQuery, queryBoth: Bool, toCallUponCompletion: ([PFObject]) -> ()){
var response = [PFObject]()
let queryCopy = query.copy() as! PFQuery
queryCopy.fromLocalDatastore()
queryCopy.findObjectsInBackgroundWithBlock{
(objects: [AnyObject]?, error: NSError?) -> Void in
if error == nil{
if objects?.count == 0{
query.findObjectsInBackgroundWithBlock{
(objects2: [AnyObject]?, error: NSError?) -> Void in
if error == nil{
response = objects2 as! [PFObject]
toCallUponCompletion(response)
}
}
}
else if queryBoth{
response = objects as! [PFObject]
var responseObjectIds = [String]()
for x in response{
responseObjectIds.append(x.objectId)
}
query.whereKey("objectId", notContainedIn: responseObjectIds)
query.findObjectsInBackgroundWithBlock{
(objects2: [AnyObject]?, error: NSError?) -> Void in
if error == nil{
response += objects2 as! [PFObject]
toCallUponCompletion(response)
}
else{
toCallUponCompletion(response)
}
}
}
else{
response = objects as! [PFObject]
toCallUponCompletion(response)
}
}
else{
println("Error being called in 'findObjectInBackgroundFromLocalDataStoreIfPossible' Error is: \(error)")
}
}
}
关闭实现:
func storeResponse (response: [PFObject]){
println(response)
}
要实现与上述函数相同的功能,但使用多个 PFQueries
,请使用以下命令:
参数差异如下:
queries
:这是您要执行查询的PFQueries
数组。顺序很重要。toCallUponCompletion
:此闭包采用带有Int
键和PFObject
值的字典作为参数,并且不返回任何内容。原因是发送查询时,它们可能无法完成并以相同的顺序返回。因此,字典中每个键值对的键是它的发送顺序,因此可以在不知道响应的实际内容的情况下使用响应。再次引用函数后面的函数闭包的实现。
功能:
func findObjectsInBackgroundFromMultipleQueriesFromLocalDataStoreIfPossible (queries: [PFQuery], queryBoth: Bool, toCallUponCompletion: ([Int: [PFObject]]) -> ()){
var responses = [Int: [PFObject]]()
for query in queries{
var response = [PFObject]()
let queryCopy = query.copy() as! PFQuery
queryCopy.fromLocalDatastore()
queryCopy.findObjectsInBackgroundWithBlock{
(objects: [AnyObject]?, error: NSError?) -> Void in
if error == nil{
if objects?.count == 0{
query.findObjectsInBackgroundWithBlock{
(objects2: [AnyObject]?, error: NSError?) -> Void in
if error == nil{
response = objects2 as! [PFObject]
responses[find(queries, query)!] = response
if responses.count == queries.count{
toCallUponCompletion(responses)
}
}
}
}
else if queryBoth{
response = objects as! [PFObject]
var ids = [String]()
for x in response{
ids.append(x.objectId)
}
query.whereKey("objectId", notContainedIn: ids)
query.findObjectsInBackgroundWithBlock{
(objects2: [AnyObject]?, error: NSError?) -> Void in
if error == nil{
response += objects2 as! [PFObject]
responses[find(queries, query)!] = response
if responses.count == queries.count{
toCallUponCompletion(responses)
}
}
}
}
else{
response = objects as! [PFObject]
responses[find(queries, query)!] = response
if responses.count == queries.count{
toCallUponCompletion(responses)
}
}
}
}
}
}
关闭实现:
func storeResponses (responses: [Int: PFObject]){
println("The response to the first query is: \(responses[0])")
println("The response to the second query is: \(responses[1])")
println("The response to the third query is: \(responses[2])")
}
非常感谢任何编辑建议。
关于swift - 同时查询解析服务器和本地数据存储,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/30055476/