将属性传递给方法时实现更清晰
我正在为我正在开发的系统编写一个 csv 导入引擎,我想避免使用看起来像这样的代码(重复 10 列):
var field = GetFieldStringValue(columnCode);
if (IsValidDecimal(field))
{
currentRow.Amount = Decimal.Parse(field);
}
else
{
ReportError();
}
最后我选择了一个看起来像这样的方法(带有重载)对于各种类型):
private void SetPropertyOrReportError(Action<decimal?> e, string columnCode)
{
if (IsValidDecimal(columnCode))
{
var fieldValue = Decimal.Parse(GetFieldStringValue(columnCode));
e(fieldValue);
}
else if (!IsColumRequired(columnCode))
{
e(null);
}
else
{
SetPropertyOrReportError();
}
}
这样,对于每一行,我最终得到的代码有点像这样:
var currentRow = new ClaimImportHelper();
SetPropertyOrReportError((e) => currentRow.ClaimantName = e, ClaimantNameColumnCode);
SetPropertyOrReportError((e) => currentRow.CustomerName = e, CustomerNameColumnCode);
SetPropertyOrReportError((e) => currentRow.CustomerProject = e, CustomerProjectColumnCode);
SetPropertyOrReportError((e) => currentRow.ClaimDate = e.Value, ClaimDateColumnCode);
SetPropertyOrReportError((e) => currentRow.ClaimSubmitted = e, ClaimSubmittedColumnCode);
SetPropertyOrReportError((e) => currentRow.ExpenseCategory = e, ExpenseCategoryColumnCode);
SetPropertyOrReportError((e) => currentRow.ExpenseType = e, ExpenseTypeColumnCode);
SetPropertyOrReportError((e) => currentRow.Amount = e.Value, AmountColumnCode);
SetPropertyOrReportError((e) => currentRow.PayeeReference = e, PayeeReferenceColumnCode);
SetPropertyOrReportError((e) => currentRow.Detail = e, DetailColumnCode);
SetPropertyOrReportError((e) => currentRow.TransactionDate = e, TransactionDateColumnCode);
parsedItems.Add(currentRow);
我认为更好,因为它更好地表达了其意图。然而,它仍然不是我想要的那样,我宁愿能够像这样调用该方法:
SetPropertyOrReportError(currentRow.ClaimantName, ClaimantNameColumnCode);
SetPropertyOrReportError(currentRow.CustomerName, CustomerNameColumnCode);
SetPropertyOrReportError(currentRow.CustomerProject, CustomerProjectColumnCode);
SetPropertyOrReportError(currentRow.ClaimDate, ClaimDateColumnCode);
SetPropertyOrReportError(currentRow.ClaimSubmitted, ClaimSubmittedColumnCode);
我遇到的问题是我无法理解如何编写一个表达式取得财产。我该怎么做?
I am writing an csv import engine for a system I'm working on and I wanted to avoid the kind of code that looks like (repeated for 10's of columns):
var field = GetFieldStringValue(columnCode);
if (IsValidDecimal(field))
{
currentRow.Amount = Decimal.Parse(field);
}
else
{
ReportError();
}
In the end I opted for a method that looks like this (with overloads for various types):
private void SetPropertyOrReportError(Action<decimal?> e, string columnCode)
{
if (IsValidDecimal(columnCode))
{
var fieldValue = Decimal.Parse(GetFieldStringValue(columnCode));
e(fieldValue);
}
else if (!IsColumRequired(columnCode))
{
e(null);
}
else
{
SetPropertyOrReportError();
}
}
That way for each row I end up with code a bit like this:
var currentRow = new ClaimImportHelper();
SetPropertyOrReportError((e) => currentRow.ClaimantName = e, ClaimantNameColumnCode);
SetPropertyOrReportError((e) => currentRow.CustomerName = e, CustomerNameColumnCode);
SetPropertyOrReportError((e) => currentRow.CustomerProject = e, CustomerProjectColumnCode);
SetPropertyOrReportError((e) => currentRow.ClaimDate = e.Value, ClaimDateColumnCode);
SetPropertyOrReportError((e) => currentRow.ClaimSubmitted = e, ClaimSubmittedColumnCode);
SetPropertyOrReportError((e) => currentRow.ExpenseCategory = e, ExpenseCategoryColumnCode);
SetPropertyOrReportError((e) => currentRow.ExpenseType = e, ExpenseTypeColumnCode);
SetPropertyOrReportError((e) => currentRow.Amount = e.Value, AmountColumnCode);
SetPropertyOrReportError((e) => currentRow.PayeeReference = e, PayeeReferenceColumnCode);
SetPropertyOrReportError((e) => currentRow.Detail = e, DetailColumnCode);
SetPropertyOrReportError((e) => currentRow.TransactionDate = e, TransactionDateColumnCode);
parsedItems.Add(currentRow);
Which I think is better since it expresses its intent better. However, it's still not as I'd like it to be, I'd rather be able to call the method like this:
SetPropertyOrReportError(currentRow.ClaimantName, ClaimantNameColumnCode);
SetPropertyOrReportError(currentRow.CustomerName, CustomerNameColumnCode);
SetPropertyOrReportError(currentRow.CustomerProject, CustomerProjectColumnCode);
SetPropertyOrReportError(currentRow.ClaimDate, ClaimDateColumnCode);
SetPropertyOrReportError(currentRow.ClaimSubmitted, ClaimSubmittedColumnCode);
The problem I'm having is that I can't get my head around how to write an Expression that will take a property. How can I do this?
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基本上你不能。
表达式 currentRow.ClaimantName 用作方法参数时,将始终表示对属性的 getter 求值的结果。
如果我们得到
infoof
运算符,可能有更好的方法 - 但目前,我认为您的 lambda 选项是最好的方法。请注意,您不需要参数周围的括号 - 例如:You can't, basically.
The expression
currentRow.ClaimantName
, when used as a method argument, will always represent the result of evaluating the getter for the property.If we ever get the
infoof
operator, there might be a better approach - but for the moment, I think your lambda option is the best one. Note that you don't need the parentheses around the parameter though - for example: