How do I append LINQ queries to each other?

Question

I have a form that filters the data depending on what they select.

I am trying to append linq queries to each other so that the end result is what they have selected on the screen.

Here is my code:

private void button_Search_Click(object sender, EventArgs e)
{
  using (var model = new SuburbanPortalEntities())
  {
    var qry = from logs in model.Logs
              select logs;

    Guid corpid;
    if (Guid.TryParse(textBox_CorporationGuid.Text, out corpid))
    {
      qry = from logs in model.Logs
                where logs.CorporationId == corpid
                select logs;
    }

    Guid tokenid;
    if (Guid.TryParse(textBox_TokenId.Text, out tokenid))
    {
      qry = from logs in model.Logs
            where logs.TokenId == tokenid
            orderby logs.LogDateTime descending 
            select logs;
    }

    if (checkBox_DisplayErrors.Checked)
    {
      qry = from logs in model.Logs
            where logs.IsException
            select logs;
    }

    if (checkBox_DisplayWarnings.Checked)
    {
      qry = from logs in model.Logs
            where logs.IsWarning
            select logs;
    }

    dataGridView1.DataSource = qry;


  }
}

I'm having no luck. The last qry in is what is displayed on my datagridview.

Can someone show me what I'm doing wrong?

Thanks !

Answer 1

What's happening here is that you're redefining qry from your source data each time. qry is an IEnumerable<T> just the same as logs, so you should be able to replace your code like so:

 var qry = model.Logs;

 if( // Condition )
    qry = qry.Where(x => x.CorporationId == corpId);

 if( // Another condition)
    qry = qry.Where(x => x.IsException);

At the end of this setup, qry will be the composition of all the selected Where clauses and should produce just the items you are looking for.

Answer 2

You can use linq Concat:

qry = qry.Concat(
            from logs in model.Logs
            where logs.CorporationId == corpid
            select logs);

On the other hand, you may want to create query based on your conditions which will select appropriate results, so you will query your data source once.