我正在编写一个简单的消息传递模块，因此一个进程可以发布消息，另一个进程可以订阅它们。我使用 EF/SqlServer 作为进程外通信机制。“服务器”只是发布者/订阅者对的共同名称（可以称为“通道”）。
我有以下方法向数据库中添加一行，表示一个名为“服务器”
public void AddServer(string name)
{
if (!context.Servers.Any(c => c.Name == name))
{
context.Servers.Add(new Server { Name = name });
}
}
我遇到的问题是，当我同时启动两个客户端时，只有一个应该添加一个新的服务器条目，但是，这不是它的工作方式。实际上，我得到了两个具有相同名称的条目的非常错误的结果，并且意识到 Any() 防护不足以解决此问题。
服务器的实体使用一个 int PK，据说我的存储库将强制执行 Name 字段的唯一性。我开始认为这行不通。
public class Server
{
public int Id { get; set; }
public string Name { get; set; }
}
我认为可以解决此问题的两种方法似乎都不理想：
- 字符串主键
- 忽略异常
这是并发的问题，对吧？
在我希望两个客户端调用具有相同名称的存储库但在数据库中仅获得具有该名称的一行的结果的情况下，我该如何处理？
更新：这是存储库代码
namespace MyBus.Data
{
public class Repository : IDisposable
{
private readonly Context context;
private readonly bool autoSave;
public delegate Chain Chain(Action<Repository> action);
public static Chain Command(Action<Repository> action)
{
using (var repo = new Data.Repository(true))
{
action(repo);
}
return new Chain(next => Command(next));
}
public Repository(bool autoSave)
{
this.autoSave = autoSave;
context = new Context();
}
public void Dispose()
{
if (autoSave)
context.SaveChanges();
context.Dispose();
}
public void AddServer(string name)
{
if (!context.Servers.Any(c => c.Name == name))
{
context.Servers.Add(new Server { Name = name });
}
}
public void AddClient(string name, bool isPublisher)
{
if (!context.Clients.Any(c => c.Name == name))
{
context.Clients.Add(new Client
{
Name = name,
ClientType = isPublisher ? ClientType.Publisher : ClientType.Subscriber
});
}
}
public void AddMessageType<T>()
{
var typeName = typeof(T).FullName;
if (!context.MessageTypes.Any(c => c.Name == typeName))
{
context.MessageTypes.Add(new MessageType { Name = typeName });
}
}
public void AddRegistration<T>(string serverName, string clientName)
{
var server = context.Servers.Single(c => c.Name == serverName);
var client = context.Clients.Single(c => c.Name == clientName);
var messageType = context.MessageTypes.Single(c => c.Name == typeof(T).FullName);
if (!context.Registrations.Any(c =>
c.ServerId == server.Id &&
c.ClientId == client.Id &&
c.MessageTypeId == messageType.Id))
{
context.Registrations.Add(new Registration
{
Client = client,
Server = server,
MessageType = messageType
});
}
}
public void AddMessage<T>(T item, out int messageId)
{
var messageType = context.MessageTypes.Single(c => c.Name == typeof(T).FullName);
var serializer = new XmlSerializer(typeof(T));
var sb = new StringBuilder();
using (var sw = new StringWriter(sb))
{
serializer.Serialize(sw, item);
}
var message = new Message
{
MessageType = messageType,
Created = DateTime.UtcNow,
Data = sb.ToString()
};
context.Messages.Add(message);
context.SaveChanges();
messageId = message.Id;
}
public void CreateDeliveries<T>(int messageId, string serverName, string sendingClientName, T item)
{
var messageType = typeof(T).FullName;
var query = from reg in context.Registrations
where reg.Server.Name == serverName &&
reg.Client.ClientType == ClientType.Subscriber &&
reg.MessageType.Name == messageType
select new
{
reg.ClientId
};
var senderClientId = context.Clients.Single(c => c.Name == sendingClientName).Id;
foreach (var reg in query)
{
context.Deliveries.Add(new Delivery
{
SenderClientId = senderClientId,
ReceiverClientId = reg.ClientId,
MessageId = messageId,
Updated = DateTime.UtcNow,
DeliveryStatus = DeliveryStatus.Sent
});
}
}
public List<T> GetDeliveries<T>(string serverName, string clientName, out List<int> messageIds)
{
messageIds = new List<int>();
var messages = new List<T>();
var clientId = context.Clients.Single(c => c.Name == clientName).Id;
var query = from del in context.Deliveries
where del.ReceiverClientId == clientId &&
del.DeliveryStatus == DeliveryStatus.Sent
select new
{
del.Id,
del.Message.Data
};
foreach (var item in query)
{
var serializer = new XmlSerializer(typeof(T));
using (var sr = new StringReader(item.Data))
{
var t = (T)serializer.Deserialize(sr);
messages.Add(t);
messageIds.Add(item.Id);
}
}
return messages;
}
public void ConfirmDelivery(int deliveryId)
{
using (var context = new Context())
{
context.Deliveries.First(c => c.Id == deliveryId).DeliveryStatus = DeliveryStatus.Received;
context.SaveChanges();
}
}
}
}