title: Query on PXFormula
body: <p>Just want to ask what could be the problem in my coding below, I want to automatically update the Tax Rate column whenever the user selects an ATC which is Tax ID technically. I successfully created a selector for ATC but it does not update the Tax Rate after selection. Below is my DAC, thanks in advance.</p>
  
  <pre><code>#region Atc
  public abstract class atc : PX.Data.IBqlField
  {
  }
  protected String _Atc;
  [PXDBString(15, IsUnicode = true)]
  [PXUIField(DisplayName = "ATC")]
  //[PXSelector(typeof(Search&lt;Tax.taxID, Where&lt;Tax.taxType, Equal&lt;CSTaxType.withholding&gt;&gt;&gt;),      
  //    new Type[] {typeof(Tax.descr)})]
  [PXSelector(typeof(Search&lt;Tax.taxID, Where&lt;Tax.taxType, Equal&lt;CSTaxType.withholding&gt;&gt;&gt;))]
  public virtual String Atc
  {
    get
    {
      return this._Atc;
    }
    set
    {
      this._Atc = value;
    }
  }      
  
  
  #endregion
  
  
  #region Atcrate
  public abstract class atcrate : PX.Data.IBqlField
  {
  }
  protected Decimal? _Atcrate;
  [PXDBDecimal()]
  [PXFormula(typeof(Selector&lt;IISI_ARAdjust_Ext.atc, TaxRev.taxRate&gt;))]
  [PXUIField(DisplayName = "ATC Rate")]
  public virtual Decimal? Atcrate
  {
      get
      {
        return this._Atcrate;
      }
      set
      {
        this._Atcrate = value;
      }
  }    
  
  #endregion
  </code></pre>