我需要检查datatable是否为null然后将行复制到datatable，否则需要将行追加到datatable。 [英] I have a requirement to check if datatable is null then copy the row to datatable otherwise need to append the row to the datatable.

问题描述

i have a requirement to check if DataTable is null then copy the row to DataTable otherwise need to append the row to the DataTable.

我尝试过：

What I have tried:

if (dtTable == null)
    {
        dtTable = (from DataRow dr in dtDetails.Rows
                   where dr["ID"].ToString() == Id
                   select dr).CopyToDataTable();
    }
    else
    {
       // Here Need to Add a new row in DataTable and append the output of 
         query into DataTable ie dtTable.

       DataRow row = selectedTable.NewRow();

        dtTable  = (from DataRow dr in dtDetails.Rows
        where dr["ID"].ToString() == Id
        select dr)
        // Need help here

    }

推荐答案

如果DataTable是 null 然后你不能复制任何东西：没有任何东西要复制！



它有点像一个口袋：你有一个口袋里面你的衬衫，用来握笔。如果你进入口袋并发现那里没有笔，你就不能在一张纸上签名 - 如果你尝试的话，你会得到非常有趣的外观！

但是你要做的就是伸进口袋，而你甚至不穿衬衫！你不能检查口袋的笔，因为口袋根本不存在。



如果你想将数据复制到DataTable并且变量是 null ，你必须创建一个表的实例来添加它。



在这种情况下，所有你需要做的是使用Add方法：

If a DataTable is null then you can't copy anything to it: there isn't anything to copy into!

It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try!
But what you are trying to do is reach into a pocket while you aren't even wearing a shirt! You can't check the pocket for a pen, because the pocket isn't there at all.

If you want to copy data to a DataTable and the variable is null, you have to create an instance of a table to add it to.

In this case, all you need to do is use the Add method:

else
    {
        dtTable.Rows.Add (from DataRow dr in dtDetails.Rows
        where dr["ID"].ToString() == Id
        select dr)

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