/// <summary>
/// Modify a Fact by Retracting it and Asserting the replacement one.
/// If the new Fact has no label (null or Empty), then the Label of the existing fact is kept.
/// </summary>
/// <param name="currentFact">The Fact to modify.</param>
/// <param name="newFact">The Fact to modify to.</param>
/// <returns>True if <term>currentFact</term> has been retracted from the FactBase, otherwise False ; this whether <term>newFact</term> already exists in the factbase, or not.</returns>
public bool Modify(Fact currentFact, Fact newFact)
{
if (Retract(currentFact)) {
// Retraction is done, let's Assert
try {
// If the new fact already exists, retract it first
if (Exists(newFact)) Retract(newFact);
// Preserve the label if no new one provided
if ((currentFact.Label != null) && (currentFact.Label != String.Empty)
&& ((newFact.Label == null) || (newFact.Label == String.Empty)))
Assert(newFact.ChangeLabel(currentFact.Label));
else
Assert(newFact);
return true;
} catch(Exception e) {
// Assert mysteriously failed: compensate the retraction
Assert(currentFact);
// and throw a wrapped exception
throw new BREException("Modify failed because Assert failed.", e);
}
}
return false;
}
public void RenameFact()
{
Fact spendingPM1 = new Fact("Spending of Peter Miller",
"spending",
new Individual("Peter Miller"),
new Individual("min(5000,EUR)"),
new Individual("previous year"));
String newLabel = "Expenses of Peter Miller";
Fact spendingPM2 = spendingPM1.ChangeLabel(newLabel);
Assert.AreEqual(spendingPM2.Label, newLabel, "Fact has been renamed");
Assert.AreEqual(spendingPM1, spendingPM2, "Renamed facts are equals");
}
