如何将2 select减为1 select linq以提高性能?

Question

我的问题很简单，但我被一些东西卡住了。你能告诉我如何在c#中将2次选择减少到1次选择吗?我正在使用CloudNative。云原生事件的NuGet包。

var orderEvents = input
.Select(_ => new OrderDocument(_.Id, _.ToString()).ToOrderEvent())
.Select(_ =>
new CloudEvent()
{
Type = _.EventType,
Subject = _.Subject,
Source = _.Source,
Data = _
});

输入是cosmosDbTrigger的一个参数，它的类型是:IReadOnlyList

OrderDocument.cs

public class OrderDocument
{
public string Id { get; private set; }
public string Json { get; private set; }
public OrderDocument(string id, string json)
{
Id = id;
Json = json;
}
public OrderEvent ToOrderEvent() => OrderEventHelper.ToOrderEvent(Json);
}

OrderEventHelper.cs

public static OrderEvent ToOrderEvent(string json)
{
ArgumentHelper.ThrowIfNullOrEmpty(json);
var orderEvent = JsonConvert.DeserializeObject<OrderEvent>(json);
var eventDefinition = OrderEvents.EventDefinitions.SingleOrDefault(_ => _.EventType == orderEvent.EventType);

return eventDefinition == null
? orderEvent
: new OrderEvent(
orderEvent.Id,
orderEvent.Source,
orderEvent.EventType,
orderEvent.Subject,
orderEvent.DataContentType,
orderEvent.DataSchema,
orderEvent.Timestamp,
JsonConvert.DeserializeObject(orderEvent.Payload.ToString(), eventDefinition.PayloadType),
orderEvent.TraceId);
}

Answer 1

linq扩展基本上是后台的for循环。如果你想对一个列表执行多个操作，也许你可以自己创建一个简单的for循环，这样你就可以自己管理了。

代码:

var orderEvents = input
.Select(_ => new OrderDocument(_.Id, _.ToString()).ToOrderEvent())
.Select(_ =>
new CloudEvent()
{
Type = _.EventType,
Subject = _.Subject,
Source = _.Source,
Data = _
});

可以改成:

// our result set, rather than the one returned from linq Select
var results = new List<CloudEvent>();
foreach(var x in input){
// create the order event here
var temporaryOrderEvent = new OrderDocument(x.Id, x.ToString()).ToOrderEvent();

// add the Cloud event to our result set
results.Add(new CloudEvent() 
{
Type = temporaryOrderEvent .EventType,
Subject = temporaryOrderEvent .Subject,
Source = temporaryOrderEvent .Source,
Data = temporaryOrderEvent 
});
}

，然后你有一个result列表工作。

如果你想保持所有的linq，你可以在第一个Select中执行所有的逻辑，并确保它返回一个CloudEvent。注意，可以在linq语句中使用花括号来计算函数，而不是单个变量值:

var orderEvents = input
.Select(x => 
{
// create the order event here
var temporaryOrderEvent = new OrderDocument(x.Id, x.ToString()).ToOrderEvent();
// return the Cloud event here
return new CloudEvent() 
{
Type = temporaryOrderEvent .EventType,
Subject = temporaryOrderEvent .Subject,
Source = temporaryOrderEvent .Source,
Data = temporaryOrderEvent 
};
});

Answer 2

如何将转换到OrderEvent和使用ToCloudEvent在相同的选择?

var orderEvents = input
.Select(_ => new OrderDocument(_.Id, _.ToString()).ToOrderEvent().ToCloudEvent())

public class OrderEvent
{
public CloudEvent ToCloudEvent()
{
new CloudEvent()
{
Type = this.EventType,
Subject = this.Subject,
Source = this.Source,
Data = this
};
}
}