aboutehlib3_2.txt

最新的 DBGRIDEH4.0

Filtering data using STFitler in DBGridEh.


One of the new feature in EhLib 3.2 is a STFilter - 
 Ability to show special row (under title) where you user enter 
 expressions in cells for filtering records in dataset. 
 (Expression in the cell can look like: "1", ">=1", ">1 AND <=5", "%TestStr%")
 When cursor reside in the filter cell they can press ENTER to apply filter.
 Expression in every cell of the STFitler is united using (By default) 
 logical operation AND.

 When user press ENTER Grid call TDBGridEh.ApplyFilter.

 At first, grid parse expression in every not empty filter cell.
 For normally parsinging the expression in cell have to have next format:

   [Operator1] Operand1 [)]  [AND|OR Operator2 Operand2 [)] ]

  Where OperatorX is one of [ = | <> | != | > | < | >= | <= | ~ | !~ | in ( ] 
  OperandX is a numeric, date or string value 
  or for the operator 'IN' it is a list of values divided by comma.

  For instance:
   1
   >=1
   >1 AND <=5
   ~ TestStr%
   !~ TestStr_
   in (1,2,3,4,5,6) and >100
   in (Str1,Str2,Str3)

  Next: If OnApplyFilter event is writed then grid call it,
  else grid call DefaultApplyFilter.
  DefaultApplyFilter apply to TDBGridEhDataService object that
  in turn try to find registered TDatasetFeaturesEh object
  for dataset that is linked to grid. If the TDatasetFeaturesEh object
  is founded then DBGridEhDataService call ApplyFilter for
  this DatasetFeatures object.

  For automatically filtering data in dataset need to add one of the units 
  EhLib... (EhLibADO, EhLibBDE, EhLibCDS) to 'uses' clause of any unit of your
  project. This units have code to register TDatasetFeaturesEh for respective
  DataSets.  Now EhLib have objects to filter data in the TClientDataSet, TQuery,
  TTable and TADOQuery. You have to write and register your own object to filter 
  data in DataSet that not present in this list or you can write 
  TDBGridEh.OnApplyFilter event for every grid.

  All of this DatasetFeatures class  based on the TSQLDatasetFeaturesEh that
  use next rules to filter data in dataset.
  1. If  STFilter.Local = True then
    SQLDatasetFeatures class build expression for local filter of DataSet 
    (TDataSet.Filter) and assign expression to TDataSet.Filter. TDataSet.Filtered 
    have to TRUE, class does not assign this property.
  2. If  STFilter.Local = False then
    class build expression for SQL 'WHERE' clause in SQL string of dataset.
    It tries to found the property that contain SQL expression.
    It tries to found string that begining from '/*Filter*/' text (By default)  
    in SQL expression and add filter expression after this text. 
    So your SQL query have to have a line that begining from '/*Filter*/' like this:
    ' select *  
      from table name 
      where
      /*Filter*/ 1=1 '


   To apply filtering on other types of datasets that is absent in above list, 
   need to write new class that inherited from TDatasetFeaturesEh or 
   TSQLDatasetFeaturesEh and register this class via RegisterDatasetFeaturesEh 
   procedure.