如何在Firebase的iOS SDK上执行分页查询？

Question

这是我的模特.

messagesRef = Firebase(url: "https://"+CONSTANTS.FirebaseDB+".firebaseio.com/messages/1:1000")
    messagesRef.queryLimitedToLast(5).observeEventType(FEventType.ChildAdded, withBlock: { (snapshot) in
        self.message_list.append(snapshot) // it works.
    });
});

我的代码有效 - 它获取最后5条消息(8-12).

但是,如果我有一个函数查询接下来的5条消息(2-6)怎么办？有一个开始和偏移.我怎么查询这个？

Answer 1

messagesRef = Firebase(url: "https://"+CONSTANTS.FirebaseDB+".firebaseio.com/messages/1:1000")messagesRef
.queryOrderedByKey()
.queryStartingAtValue(5)
.queryEndingAtValue(10)
.observeEventType(FEventType.ChildAdded, withBlock: { (snapshot) in self.message_list.append(snapshot) });

这是一个在黑暗中的镜头,但它似乎应该基于这里的文档https://www.firebase.com/docs/ios-api/Classes/Firebase.html#//api/name/queryStartingAtValue:

Answer 2

花了太多时间我已经弄明白了,这就是解决方案.这是Objective-C代码,您可以将其转换为swift.调用以下功能以进行寻呼.

- (void)loadMoreMessages {

    if (!lastMessageKey) {
        // Loading messages first time
        [[[msgsReference queryOrderedByKey] queryLimitedToLast:K_MESSAGES_PER_PAGE] observeSingleEventOfType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot * _Nonnull snapshot) {
            if (snapshot.exists) {

                for (FIRDataSnapshot *child in snapshot.children) {

                    NSMutableDictionary *dict = [child.value mutableCopy];
                    [dict setObject:child.key forKey:@"id"];
                    [messages addObject:dict];
                }

                lastMessageKey = [[snapshot.children.allObjects firstObject] key];
                NSLog(@"%@", messages);
            }
        }];
    }
    else {
        // Paging started
        [[[[msgsReference queryOrderedByKey] queryLimitedToLast:K_MESSAGES_PER_PAGE + 1] queryEndingAtValue:lastMessageKey] observeSingleEventOfType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot * _Nonnull snapshot) {

            if (snapshot.exists) {

                NSInteger count = 0;
                NSMutableArray *newPage = [NSMutableArray new];
                for (FIRDataSnapshot *child in snapshot.children) {

                    // Ignore last object because this is duplicate of last page
                    if (count == snapshot.childrenCount - 1) {
                        break;
                    }

                    count += 1;
                    NSMutableDictionary *dict = [child.value mutableCopy];
                    [dict setObject:child.key forKey:@"id"];
                    [newPage addObject:dict];
                }

                lastMessageKey = [[snapshot.children.allObjects firstObject] key];

                // Insert new messages at top of old array
                NSIndexSet *indexes = [NSIndexSet indexSetWithIndexesInRange: NSMakeRange(0, [newPage count])];
                [messages insertObjects:newPage atIndexes:indexes];
                NSLog(@"%@", messages);
            }
        }];
    }
}

这里是您需要的对象的描述:

#define K_MESSAGES_PER_PAGE 50 // A macro defining the numbers in one request
msgsReference // Firebase database messages node reference I'm also attaching the screenshot of my db structure for make you more clear
lastMessageKey // Is a NSString object which store the first key of last page
messages // Is a NSMutableArray storing the result

祝好运!!(y)的