LambdaJ: matching on fields of the same object

Question

Can someone get me out of LambdaJ pit I fell into please?

let's assume I have a list of objects of this class:

private class TestObject {
    private String A;
    private String B;
    //gettters and setters
}

Let's say I want to select the objects from the list where A.equals(B)

I tried this:

 List<TestObject> theSameList = select(testList, having(on(TestObject.class).getA(), equalTo(on(TestObject.class).getB())));

but this returns an empty list

And this:

List<TestObject> theSameList = select(testList, having(on(TestObject.class).getA().equals(on(TestObject.class).getB())));

but that throws an exception [EDIT: due to known limitations of proxying final classes]

Note, One way of getting around this is to have a method that compares the two fields inside the TestObject, but let's assume I cannot do this for a reason of your choice.

What am I missing?

Answer 1

After poking and fiddling with LambdaJ to match on the fields of the same object, the only solution that is working for me is writing a custom matcher. Here's quick and dirty implementation of one that would do the job:

private Matcher<Object> hasPropertiesEqual(final String propA, final String propB) {
    return new TypeSafeMatcher<Object>() {


        public void describeTo(final Description description) {
            description.appendText("The propeties are not equal");
        }

        @Override
        protected boolean matchesSafely(final Object object) {

            Object propAValue, propBValue;
            try {
                propAValue = PropertyUtils.getProperty(object, propA);
                propBValue = PropertyUtils.getProperty(object, propB);
            } catch(Exception e) {

                return false;
            }

            return propAValue.equals(propBValue);
        }
    };
}

The PropertyUtils is the class from org.apache.commons.beanutils

The way to use this matcher:

List<TestObject> theSameList = select(testList, having(on(TestObject.class), hasPropertiesEqual("a", "b")));