如何从文本框C＃在LINQ中接受输入

Question

I have a data table dt_Customers which contains some customers information. In this data table I want to select a range of ZIP codes which the user will enter using a text box.

I am using following code:

IEnumerable<DataRow> enumerableDataRowCollection =
   from company in dt_Customers.AsEnumerable()
   let zip = company.Field<string>("ZIP")
   where (!string.IsNullOrEmpty(zip) && (zip[0] >= "'" + txtBox_ZIP_From.Text + "'" && zip[0] <=  "'" + txtBox_ZIP_to.Text + "'"))

   select company;

But I am getting an error

Operator '>=' cannot be applied to operands of type 'char' and 'string'

The above code works fine when I hard code some value, like this:

zip[0] >= '2' && zip[0] <= '6'

Answer 1

Zip[0] is a character, and txtBox_ZIP_From.Text is a String. In the given hard-coded example you're comparing a character and a character.

Answer 2

IEnumerable<DataRow> enumerableDataRowCollection =
   from company in dt_Customers.AsEnumerable()
   let zip = company.Field<string>("ZIP")
   where (!string.IsNullOrEmpty(zip) && (zip >= txtBox_ZIP_From.Text && zip <=  txtBox_ZIP_to.Text))

if txtBox contient a singel char

var cCriterFrom = txtBox_ZIP_From.Text.Text[0];
var cCriterTo = txtBox_ZIP_to.Text.Text[0];

IEnumerable<DataRow> enumerableDataRowCollection =
   from company in dt_Customers.AsEnumerable()
   let zip = company.Field<string>("ZIP")
   where (!string.IsNullOrEmpty(zip) && (zip[0] >= cCriterFrom && zip[0] <= cCriterTo))

Answer 3

The problem is that zip is a string , so zip[n] is a char . If you want to compare strings, try this:

string.Compare(zip, txtBox_ZIP_From.Text) >= 0 &&
string.Compare(zip, txtBox_ZIP_To.Text) <= 0

However, it might be better to convert zip and the text box inputs to numbers, and compare them that way.

Or if you just want to compare the first characters in each string, you can use this:

zip[0] >= txtBox_ZIP_From.Text[0] && zip[0] <=  txtBox_ZIP_to.Text[0]

Answer 4

Try this:

IEnumerable<DataRow> enumerableDataRowCollection =
   from company in dt_Customers.AsEnumerable()
   let zip = company.Field<string>("ZIP")
   where (!string.IsNullOrEmpty(zip) && (zip.CompareTo(txtBox_ZIP_From.Text) >= 0) && (zip.CompareTo(txtBox_ZIP_to.Text) <=0))    
   select company;