Combining Predicates

A predicate can be composed of other predicates by means of the and() and or() methods as shown in the examples below.

and

The and() method returns a composed predicate that represents a short-circuiting logical AND of a first predicate and another given second predicate. If the first predicate is evaluated to false, then the second predicate is not evaluated.

The following code sample will print out all films that are long (apparently a film is long when its length is greater than 120 minutes) and that has a rating that is "PG-13":

Predicate<Film> isLong = Film$.length.greaterThan(120);
Predicate<Film> isPG13 = Film$.rating.equal("PG-13");

jpaStreamer.stream(Film.class)
    .filter(isLong.and(isPG13))
    .forEachOrdered(System.out::println);

This will produce the following output:

Film { filmId = 33, title = APOLLO TEEN, ... , length = 153, ..., rating = PG-13, ...
Film { filmId = 35, title = ARACHNOPHOBIA ROLLERCOASTER, ..., length = 147, ..., rating = PG-13, ...
Film { filmId = 36, title = ARGONAUTS TOWN, ..., length = 127, ..., rating = PG-13, ...
...

The same result can be achieved by just stacking two filter operations on top of each other. So this:

jpaStreamer.stream(Film.class)
    .filter(Film$.length.greaterThan(120))
    .filter(Film$.rating.equal("PG-13"))
    .forEachOrdered(System.out::println);

is equivalent to:

jpaStreamer.stream(Film.class)
    .filter(Film$.length.greaterThan(120).and(Film$.rating.equal("PG-13"))
    .forEachOrdered(System.out::println);

or

The or() method returns a composed predicate that represents a short-circuiting logical OR of a first predicate and another given second predicate. If the first predicate is evaluated to true, then the second predicate is not evaluated.

The following code sample will print out all films that are either long (length > 120) or has a rating of "PG-13":

Predicate<Film> isLong = Film$.length.greaterThan(120);
Predicate<Film> isPG13 = Film$.rating.equal("PG-13");

jpaStreamer.stream(Film.class)
    .filter(isLong.or(isPG13))
    .forEachOrdered(System.out::println);

This will produce the following output:

Film { filmId = 5, title = AFRICAN EGG, ..., length = 130, ..., rating = G, ...
Film { filmId = 6, title = AGENT TRUMAN, ..., length = 169, ..., rating = PG, ...
Film { filmId = 7, title = AIRPLANE SIERRA, ..., length = 62, ..., rating = PG-13, ...
...

As for the and() method, there is an equivalent way of expressing compositions with or(). Here is an example of how streams can be concatenated to obtain the same functionality as above:

StreamComposition.concatAndAutoClose(
    jpaStreamer.stream(Film.class).filter(Film$.length.greaterThan(120)),
    jpaStreamer.stream(Film.class).filter(Film$.rating.equal("PG-13"))
    )
    .distinct()
    .forEachOrdered(System.out::println);

Film { filmId = 5, title = AFRICAN EGG, ..., length = 130, ..., rating = G, ...
Film { filmId = 6, title = AGENT TRUMAN, ..., length = 169, ..., rating = PG, ...
{... a number of films with length > 120}
Film { filmId = 7, title = AIRPLANE SIERRA, ..., length = 62, ..., rating = PG-13, ...
{... a number of films with rating = "PG-13}
...

In this case, optimized queries will be used for the two sub-streams but the films must be handled by the JVM from the .distinct() operation.

JPAstreamer can optimize Predicate::or better than a concatenation of streams followed by a distinct() operation.