C# 并发字典未在 Azure 函数中添加或更新值

问题描述

我试图将一些键值对缓存到一个并发字典中，以避免每次我需要该值时都去宇宙。这是我的代码。

public class activitylogHubIngress
    {
        private readonly ICustomerDbService _customerDbService;
        
        private static ConcurrentDictionary<string,string> _customerIdLookup => new ConcurrentDictionary<string,string>(StringComparer.InvariantCultureIgnoreCase);

        public activitylogHubIngress(ICustomerDbService customerDbService)
        {
            _customerDbService = customerDbService;
        }

        [FunctionName("activitylogHubIngress")]
        public async Task Run([EventHubTrigger("activity-log-events",Connection = "activitylogEventHub")] EventData[] events,ILogger log)
        {
         //Some code removed for brevity. At some point in this Azure Function the following line gets called to retrieve a customer ID.
         
         string customerId = await GetCustomerId(activitylogHubEvent.SubscriptionId,log); 

         //Some code removed for brevity. 
        }

private async Task<string> GetCustomerId(string subscriptionId,ILogger log = null)
        {
            if (_customerIdLookup.TryGetValue(subscriptionId,out string customerId))
            {
                return customerId;
            }

            var customer = await _customerDbService.GetCustomerBySubscription(subscriptionId);
            if(customer is null)
            {
                _customerIdLookup.AddOrUpdate(subscriptionId,string.Empty,(key,value) => string.Empty);

                if (log != null)
                {
                    log.Loginformation(ApplicationEvents.activitylogUnkNownSubscriptionFailure,$"Added Non-Customer ({subscriptionId}: null) to _customerIdLookup" +
                    $"\nListing _customerIdLookup dictionary (item count {_customerIdLookup.Count})" +
                    $"\n{string.Join("\n",_customerIdLookup.Keys.Select(k => $"{k}: {_customerIdLookup[k]}").ToList())}");
                }

                return null;
            }

            _customerIdLookup.AddOrUpdate(subscriptionId,customer.Id,value) => customer.Id);

            if(log != null)
            {
                log.Loginformation(ApplicationEvents.activitylogUnkNownSubscriptionFailure,$"Added ({subscriptionId}: {customer.Id}) to _customerIdLookup" +
                $"\nListing _customerIdLookup dictionary (item count {_customerIdLookup.Count})" +
                $"\n{string.Join("\n",_customerIdLookup.Keys.Select(k => $"{k}: {_customerIdLookup[k]}").ToList())}");
            }                

            return customer.Id;
        }

代码执行正常，但意图是返回值

var customer = await _customerDbService.GetCustomerBySubscription(subscriptionId);

将缓存在 _customerIdLookup 中，然后在下一个具有相同订阅 ID 的事件时通过字典访问，而不是转到 cosmos。但是，_customerIdLookup 仍然为空，即使我使用相同的订阅 ID 发送多个事件，代码也始终通过 Cosmos 进行路由。

我所有的日志看起来都像这样。

Added (84b*****-****-****-****-***********0f: 12345678) to _customerIdLookup
Listing _customerIdLookup dictionary (item count 0)

项目计数始终为零。

我做错了什么，字典没有被写入？

解决方法

问题在于你对字典的声明：

private static ConcurrentDictionary<string,string> _customerIdLookup => new ConcurrentDictionary<string,string>(StringComparer.InvariantCultureIgnoreCase);

注意 lambda 符号 =>，这意味着每次访问成员时都会返回一个新实例。