23 Sep 2012

Dynamic view criterias from where clauses

Let's consider a use-case when a system administrator or a business administrator or even a user can define some user-filters. These user filters are going to be stored in some storage, for example a database, and at run-time an end user can apply these filters to their data in UI. These filters contain just simple Where SQL clauses. For example, we have in the application some entity "Boats" and it has some predefined user filters:

It would be cool to dynamically create and add View Criterias to the VO definition and to work with them in a usual way. For example, we could use standard af:query component, where a user can select a criteria from the list and apply it to the data in a table. But the question is: how to create View Criterias having only simple where clause strings?
A View Criteria consists of view criteria rows, and a view criteria row consists of view criteria items, and a view criteria item consists of a view object attribute, an operation type like equal, less, like or whatever and an operand, literal or bind variable. The framework at run-time generates appropriate where clauses from these criteria items and applies them to the SQL query. But we don’t have all these cool things – an attribute, an operation type and an operand, we just have a where clause string and nothing else.
The trick is to put this string into the value property of the view criteria item and override a view object method getCriteriaItemClause responsible for generating a where clause from a view criteria item:

   @Override
  public String getCriteriaItemClause(ViewCriteriaItem crieriaItem) {
      return (String) crieriaItem.getValue(); 
   }  

The method is just going to return back a criteria item’s value. And we can add a method to the custom ViewDefImpl class:

    private void createViewCriterias(RowIterator userFilters){
      while (userFilters.hasNext()) {
        VAgileEntityFilterRowImpl userFilter = (VAgileEntityFilterRowImpl) userFilters.next();
        //Create a View Criteria
        ViewCriteriaImpl viewCriteria =  (ViewCriteriaImpl) createViewCriteria();
        viewCriteria.setName(userFilter.getName());
        
        //Create a View Criteria Row
        ViewCriteriaRow vcr = viewCriteria.createViewCriteriaRow();
        
        //Get the first attribute from the VO's attribute list
        String firstAttributeName = getAttributeDef(0).getName();
        //And create a View Criteria Item for this attribute
        ViewCriteriaItem vci = new ViewCriteriaItem(firstAttributeName, vcr);
        
        //Set the Where clause string as a value of the 
        //View Criteria Item instance
        vci.setValue(userFilter.getWhereclause());
        
        //Add the View Criteria Item instance to the View Criteria Row
        vcr.addCriteriaItem(firstAttributeName, vci);        
        
        //Add the View Criteria Row instance to the View Criteria
        viewCriteria.add(vcr);
            
        //Add the View Criteria instance to the View Definition
        putViewCriteria(viewCriteria.getName(), viewCriteria);
        
      }
    }
 
A View Criteria Item can be created for some VO's attribute only. But we’ve overridden generating of a where clause from a view criteria item. So, it doesn't matter for which particular attribute it's going to be created.  Therefore, we can just take the first attribute from the list and pass it to the ViewCriteriaItem constructor. Actually, that's it. And now we can work with these View Criterias in a usual way.

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