A concept for making JPA queries type-safe using code generation.

TypeSafeJPA.java

public class TypeSafeJPA {

    class MyBean {

        private String foo;

        private int bar;

        public String getFoo() {
            return foo;
        }

        public void setFoo(String foo) {
            this.foo = foo;
        }

        public int getBar() {
            return bar;
        }

        public void setBar(int bar) {
            this.bar = bar;
        }
    }

    @Test
    public void testAPI() throws Exception {
        Selection<MyBean> myBeanSelection = select(MyBean.class);
        myBeanSelection.where().setFoo("bar");
        myBeanSelection.or().setFoo("bar2");
        myBeanSelection.where().setBar(23156);
        //Selection<MyBean> copy = myBeanSelection.clone();
        MyBean databaseLookup = myBeanSelection.uniqueResult();
    }


    static <T> Selection<T> select(Class<T> type) {
        return new Selection<T>(type);
    }

    static class Selection<T> {

        private final Class<T> type;

        private final List<String> criteria = new ArrayList<String>();

        Selection(Class<T> type) {
            this.type = type;
        }

        T where() {
            try {
                return new ByteBuddy()
                        .subclass(type)
                        .method(any()).intercept(MethodDelegation.to(this).filter(named("where")))
                        .make()
                        .load(type.getClassLoader(), ClassLoadingStrategy.Default.WRAPPER)
                        .getLoaded()
                        .newInstance();
            } catch (Exception e) {
                throw new RuntimeException();
            }
        }

        T or() {
            try {
                return new ByteBuddy()
                        .subclass(type)
                        .method(any()).intercept(MethodDelegation.to(this).filter(named("or")))
                        .make()
                        .load(type.getClassLoader(), ClassLoadingStrategy.Default.WRAPPER)
                        .getLoaded()
                        .newInstance();
            } catch (Exception e) {
                throw new RuntimeException();
            }
        }

        void where(@Argument(0) Object arg, @Origin Method m) {
            criteria.add("Make sure that " + m.getName() + " is " + arg);
        }

        void or(@Argument(0) Object arg, @Origin Method m) {
            criteria.add("or make sure that " + m.getName() + " is " + arg);
        }

        public T uniqueResult() {
            for (String s : criteria) {
                System.out.println(s);
            }
            return null; // Query JPA
        }
    }
}