javax.sql.rowset.Predicate — clojure-interop/javax.sql 1.0.5

The standard interface that provides the framework for all FilteredRowSet objects to describe their filters.

1.0 Background The Predicate interface is a standard interface that applications can implement to define the filter they wish to apply to a a FilteredRowSet object. A FilteredRowSet object consumes implementations of this interface and enforces the constraints defined in the implementation of the method evaluate. A FilteredRowSet object enforces the filter constraints in a bi-directional manner: It outputs only rows that are within the constraints of the filter; and conversely, it inserts, modifies, or updates only rows that are within the constraints of the filter.

2.0 Implementation Guidelines In order to supply a predicate for the FilteredRowSet. this interface must be implemented. At this time, the JDBC RowSet Implementations (JSR-114) does not specify any standard filters definitions. By specifying a standard means and mechanism for a range of filters to be defined and deployed with both the reference and vendor implementations of the FilteredRowSet interface, this allows for a flexible and application motivated implementations of Predicate to emerge.

A sample implementation would look something like this:

public class Range implements Predicate {

  private int[] lo;
  private int[] hi;
  private int[] idx;

  public Range(int[] lo, int[] hi, int[] idx) {
     this.lo = lo;
     this.hi = hi;
     this.idx = idx;
  }

 public boolean evaluate(RowSet rs) {

     // Check the present row determine if it lies
     // within the filtering criteria.

     for (int i = 0; i < idx.length; i++) {
        int value;
        try {
            value = (Integer) rs.getObject(idx[i]);
        } catch (SQLException ex) {
            Logger.getLogger(Range.class.getName()).log(Level.SEVERE, null, ex);
            return false;
        }

        if (value < lo[i] && value > hi[i]) {
            // outside of filter constraints
            return false;
        }
    }
    // Within filter constraints
   return true;
 }

}

The example above implements a simple range predicate. Note, that implementations should but are not required to provide String and integer index based constructors to provide for JDBC RowSet Implementation applications that use both column identification conventions.

evaluate clj

(evaluate this rs)

(evaluate this value column)

This method is called by a FilteredRowSet object to check whether the value lies between the filtering criterion (or criteria if multiple constraints exist) set using the setFilter() method.

The FilteredRowSet object will use this method internally while inserting new rows to a FilteredRowSet instance.

value - An Object value which needs to be checked, whether it can be part of this FilterRowSet object. - java.lang.Object column - a int object that must match the SQL index of a column in this RowSet object. This must have been passed to Predicate as one of the columns for filtering while initializing a Predicate - int

returns: true if row value lies within the filter; false otherwise - boolean

throws: java.sql.SQLException - if the column is not part of filtering criteria