[英]Factory class using generics but without base class
我得到了我認為可能是一個不尋常的問題(我已經搜索了很多答案,但我不認為我找到了一個)。
我有從隊列中讀取的消息,並且根據消息類型包含需要反序列化為具體c#類的有效負載。 這需要最終具體(我不能使用泛型)因為我使用表達式樹對從隊列到達的類執行評估。
基類如下所示:
public abstract class BaseRuleMessage<T>
{
public abstract Func<T, bool> CompileRule(Rule r, T msg);
public T Deserialize(ClientEventQueueMessage message)
{
return JsonConvert.DeserializeObject<T>(message.Payload);
}
public BaseRuleMessage()
{
RulesCompleted = new List<int>();
}
public IEnumerable<Rule> FilterRules(RuleGroup ruleGroup)
{
return ruleGroup.Rules.Where(item =>
!RulesCompleted.Any(r => r.Equals(item.Id)));
}
我像這樣實現基類:
public class UiTransactionUpdate : BaseRuleMessage<UiTransactionUpdate>
{
public override Func<UiTransactionUpdate, bool> CompileRule(Rule r, UiTransactionUpdate msg)
{
var expression = Expression.Parameter(typeof(UiTransactionUpdate));
Expression expr = BuildExpr(r, expression, msg);
return Expression.Lambda<Func<UiTransactionUpdate, bool>>(expr, expression).Compile();
}
public Guid TransactionId { get; set; }
public Guid GroupId { get; set; }
public decimal StatusValue { get; set; }
然后我做這樣的事情來打電話:
switch (message.MessageType)
{
case "UI_UPDATE":
{
message.Payload = RemoveNullGroupIdReference(jsonPayload, message.Payload);
var deserializedMessage = new UiTransactionUpdate().Deserialize(message);
deserializedMessage.RulesCompleted = deserializedMessage.RulesCompleted ?? new List<int>();
foreach (var rule in deserializedMessage.FilterRules(ruleGroup))
{
我真正想知道的是如何創建一個工廠(或者我可以嗎?)能夠以這樣一種方式定義基類的實現,即我可以返回一個具體的類來用於我的表達式樹評估而不需要重復每種類型的所有調用代碼。
我避免使用dynamic
但這意味着我已經將對象作為object
傳遞。 我不喜歡使用dynamic
但在這種情況下,在運行時投射對象可能不會更好。
我還必須更改代碼,以便不是返回Func<T, bool>
,而是有一個執行Func
。 這是為了避免引用泛型類。 我不確定你的實際實現中是否真的需要Func
。
我不得不創建一個通常不輸入的新基類。
// Horrible name, do change it to something more appropriate
public abstract class BaseBaseRuleMessage
{
public IList<int> RulesCompleted { get; set; }
public IEnumerable<Rule> FilterRules(RuleGroup ruleGroup)
{
return ruleGroup.Rules.Where(item =>
!RulesCompleted.Any(r => r.Equals(item.Id)));
}
public BaseBaseRuleMessage DeserializeToBaseBaseRuleMessage(ClientEventQueueMessage message)
{
return (BaseBaseRuleMessage) DeserializeToType(message);
}
protected abstract object DeserializeToType(ClientEventQueueMessage message);
public abstract bool ExecuteRule(Rule rule, object msg);
}
更新了BaseRuleMessage
以從BaseBaseRuleMessage
派生(並將一些屬性移動到基類。
public abstract class BaseRuleMessage<T> : BaseBaseRuleMessage
where T : BaseRuleMessage<T>
{
public abstract Func<T, bool> CompileRule(Rule r, T msg);
protected override object DeserializeToType(ClientEventQueueMessage message)
{
return JsonConvert.DeserializeObject(message.Payload, typeof(T));
}
protected BaseRuleMessage()
{
RulesCompleted = new List<int>();
}
public override bool ExecuteRule(Rule rule, object msg)
{
var message = (T) msg;
if (message == null)
{
throw new InvalidOperationException();
}
return CompileRule(rule, message).Invoke(message);
}
}
具體類基本相同。 我已經實現了自己的BuildExpr
,以確保代碼可以編譯。
public class UiTransactionUpdate : BaseRuleMessage<UiTransactionUpdate>
{
public override Func<UiTransactionUpdate, bool> CompileRule(Rule r, UiTransactionUpdate msg)
{
var expression = Expression.Parameter(typeof(UiTransactionUpdate));
Expression expr = BuildExpr(r, expression, msg);
return Expression.Lambda<Func<UiTransactionUpdate, bool>>(expr, expression).Compile();
}
public Guid TransactionId { get; set; }
public Guid GroupId { get; set; }
public decimal StatusValue { get; set; }
private Expression BuildExpr(Rule rule, ParameterExpression parameterExpression, UiTransactionUpdate message)
{
var transactionIdProperty = Expression.Property(parameterExpression, "TransactionId");
var value = Expression.Constant(rule.TransactionId);
return Expression.Equal(transactionIdProperty, value);
}
}
要使用它:
var messageTypeToTypeMap = new Dictionary<string, Func<BaseBaseRuleMessage>>
{
{"UI_UPDATE", () => new UiTransactionUpdate()}
};
var factoryFunc = messageTypeToTypeMap[message.MessageType];
message.Payload = RemoveNullGroupIdReference(jsonPayload, message.Payload);
var ruleMessage = factoryFunc.Invoke();
var deserializedMessage = ruleMessage.DeserializeToBaseBaseRuleMessage(message);
deserializedMessage.RulesCompleted = deserializedMessage.RulesCompleted ?? new List<int>();
foreach (var rule in deserializedMessage.FilterRules(ruleGroup))
{
var isTrue = deserializedMessage.ExecuteRule(rule, deserializedMessage);
}
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