当你有行时，使用LINQ从列名中获取列值？

I'm trying to convert some code that uses datasets to LINQ. Some of the code passes column names into other functions as strings.

我正在尝试将一些使用数据集的代码转换为LINQ。一些代码将列名称作为字符串传递给其他函数。

Is there anyway I can easily rewrite this into LINQ?

无论如何,我可以轻松地将其重写为LINQ?

string s = getElement(tr, elementName);

private string getElement (tableRow re, string elementName){
    if(tr[elementName] != null){
       return tr[elementName].toString()
    }
}

OR:

private void copy (tableRow trFrom, tableRow trTo){
   foreach (DataColumn c in trFrom.Table.Columns) {
        trTo[c.ColumnName] = trFrom[c.ColumnName];
   }
}

Answer to GVS: The reason to convert to LINQ is because it in many situations are easier to code LINQ and get better performance. It's related to another question here on *: programming pattern using typed datasets

回答GVS:转换为LINQ的原因是因为它在很多情况下更容易编写LINQ代码并获得更好的性能。它与*中的另一个问题有关:使用类型化数据集的编程模式

The reason I need to use the column name as a string is mainly because the column names are passed as a ID for input fields, they are then sent back to the program using AJAX (jquery).

我需要将列名用作字符串的原因主要是因为列名作为输入字段的ID传递,然后使用AJAX(jquery)将它们发送回程序。

3 个解决方案

#1

1. Simple way

   1.1. Using IEnumerable (Linq to Objects or similar) Change the elementName parameter for a Func and pass lambdas instead (you will get compile time checking as well!)

   1.1。使用IEnumerable(Linq to Objects或类似)更改Func的elementName参数并改为传递lambdas(您也​​将获得编译时检查!)

   1.2. Using IQueryable (Linq to SQL or similar) Same, but use Expression> instead.

   1.2。使用IQueryable(Linq to SQL或类似)相同,但使用Expression>。

2. Complex way: If for some reason you need to keep the parameter as an string (maybe is introduced by user) You can use reflection to build an expression tree at runtime http://msdn.microsoft.com/en-us/library/system.linq.expressions.expression.aspx.

   复杂的方式:如果由于某种原因你需要将参数保存为字符串(可能由用户介绍)你可以使用反射在运行时构建表达式树http://msdn.microsoft.com/en-us/library/ system.linq.expressions.expression.aspx。

   2.1. Using IEnumerable Then Compile, and use it as a parameter in a where, select...

   2.1。使用IEnumerable然后编译,并将其用作where中的参数,选择...

   2.2. Using IQueryable Use it as a parameter in the where, select,

   2.2。使用IQueryable将其用作where,select中的参数,

If you need to compose the lambda with other lambdas use this cool technique http://tomasp.net/blog/linq-expand.aspx

如果你需要用其他lambda编写lambda,请使用这个很酷的技术http://tomasp.net/blog/linq-expand.aspx

#2

The answer is to use reflection.

答案是使用反射。

Getting a value

获得价值

private string getElement (tableRow tr, string element){
    string val = "";
    try
    {
        val = tr.GetType().GetProperty(element).GetValue(tr, null).ToString();
    }
    catch //NULL value
    {
        val = "";
    }
}

Or the copy scenario:

或复制方案:

foreach (PropertyInfo c in tr.GetType().GetProperties())
{
    thr.GetType().GetProperty(c.Name).SetValue(thr,
         tr.GetType().GetProperty(c.Name).GetValue(tr, null), null);
}

#3

Why would you convert working and clear code into something using LINQ?

为什么要使用LINQ将工作和清除代码转换为某些内容?

Edit: LINQ is nice, cool stuff. But don't make the same errors as many XML fans did (specially first-adapters), by applying it to everything.

编辑:LINQ很好,很酷。但是,不要像许多XML粉丝那样做出同样的错误(特别是第一个适配器),将其应用于所有内容。