C# 检查 DataRow 是否包含特定列的最佳实践
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Best practice to check if DataRow contains a certain column
提问by Konrad Viltersten
At the moment, when I iterate over the DataRowinstances, I do this.
目前，当我遍历DataRow实例时，我会这样做。
foreach(DataRow row in table)
return yield new Thingy { Name = row["hazaa"] };
Sooner of later (i.e. sooner), I'll get the tableto be missing the column donkeyand the poo will hit the fan. After some extensive googling (about 30 seconds) I discovered the following protection syntax.
的迟早（即更快），我会得到表失踪列驴和便便将达到风扇。经过一些广泛的谷歌搜索（大约 30 秒），我发现了以下保护语法。
foreach(DataRow row in table)
if(row.Table.Columns.Contains("donkey"))
return yield new Thingy { Name = row["hazaa"] };
else
return null;
Now - is this the simplest syntax?! Really? I was expecting a method that gets me the field if it exists or nullotherwise. Or at least a Containsmethod directly on the row.
现在 - 这是最简单的语法吗？！真的吗？我期待一种方法，如果它存在，则可以获取该字段，否则为null。或者至少直接在行上包含一个方法。
Am I missing something? I'll be mapping in many fields that way so the code will look dreadfully unreadable...
我错过了什么吗？我将以这种方式在许多领域进行映射，因此代码看起来非常不可读......
采纳答案by Varun K
You can create an extension method to make it cleaner:
您可以创建一个扩展方法以使其更清晰：
static class DataRowExtensions
{
public static object GetValue(this DataRow row, string column)
{
return row.Table.Columns.Contains(column) ? row[column] : null;
}
}
Now call it like below:
现在像下面这样调用它：
foreach(DataRow row in table)
return yield new Thingy { Name = row.GetValue("hazaa") };
回答by Heslacher
As your DataTable table always has the same columns ( they won`t change for any row ) you only need to check for the columnname once.
由于您的 DataTable 表始终具有相同的列（它们不会为任何行更改），您只需要检查一次列名。
if (table.Columns.Contains("donkey"))
{
foreach ...
}
回答by Driton
foreach (DataColumn item in row.Table.Columns)
{
switch (item.ColumnName)
{
case "ID":
{
p.ID = Convert.ToInt32(row[item.ColumnName].ToString());
}
break;
case "firstName":
{
p.firstName = row[item.ColumnName].ToString();
}
break;
case "lastName":
{
p.lastName = row[item.ColumnName].ToString();
}
break;
default:
break;
};
}
回答by howcheng
To build on the answer by Varun K, use a generic type parameter:
要以 Varun K 的答案为基础，请使用泛型类型参数：
public static T GetValue<T>(this DataRow row, string column)
{
if (!row.Table.Columns.Contains(column))
return default(T);
object value = row[ColumnName];
if (value == DBNull.Value)
return default(T);
return (T)value;
}
