LINQ查询不返回字符串比较中的行

Question

I'm new to writing LINQ queries, and I'm having trouble with string comparisons. I'm loading the data into a DataTable (confirmed that table in SQL DB and DataTable have same number of rows), but for some reason I can't find a value that I know exists in both.

The text box contains 'servername' while the datarows contain 'servername.mydomain.net', so here's what my code looks like

string strParameter = txtAutoComplete.ToString().ToLower();

    //WUG TableAdapter and DataTable
    dsCIInfoTableAdapters.DeviceTableAdapter taWUG;
    taWUG = new dsCIInfoTableAdapters.DeviceTableAdapter();

    dsCIInfo.DeviceDataTable dtWUG = new dsCIInfo.DeviceDataTable();
    taWUG.Fill(dtWUG);

    var qstWUG = (from row in dtWUG.AsEnumerable()
                  where row.Field<string>("sDisplayName").ToLower().Contains(strParameter)
                  select row.Field<string>("sDisplayName"));

Answer 1

Beleive in your LINQ statement dtWUG needs to be dtWUG.AsEnumerable(). Linq only works on data sources that implement the IEnumerable Interface.

Answer 2

You can debug it easier if you add some let statements where you can add breakpoints:

    var qstWUG = (from row in dtWUG
                  let display = row.Field<string>("sDisplayName")
                  let lower = display.ToLower()
                  let contains = lower.Contains(strParameter)
                  where contains
                  select display).ToArray();

Also convert it to an array using .ToArray() at the end, will make it execute immediately (LINQ is lazy by paradigm, doesn't execute until it's needed), and also easier to look at in subsequent breakpoints.

Answer 3

Yeah, I feel stupid... I forgot to use the textbox.text to assign it to a string

string strParameter = txtAutoComplete.Text.ToLower();


        //WUG TableAdapter and DataTable
        dsCIInfoTableAdapters.DeviceTableAdapter taWUG;
        taWUG = new dsCIInfoTableAdapters.DeviceTableAdapter();

        dsCIInfo.DeviceDataTable dtWUG = new dsCIInfo.DeviceDataTable();
        taWUG.Fill(dtWUG);

        var qstWUG = (from row in dtWUG.AsEnumerable()
                      let display = row.Field<string>("sDisplayName")
                      where display.ToLower().Contains(strParameter)
                      select display).ToArray();