Work harder not smarter

me Gerrit Meier Staff Software Engineer @ Neo4j

Why? How am I supposed to work even harder?

Why? How am I supposed to work even harder? !Most examples are over-simplified!

User Movie Actor Rating

User Rating Movie Actor uuid createdAt / updatedAt / etc. name dob …. uuid createdAt / updatedAt / etc. title stars …. uuid createdAt / updatedAt / etc. title plot …. uuid createdAt / updatedAt / etc. name dob ….

User Rating Movie Actor uuid createdAt / updatedAt / etc. name dob …. uuid createdAt / updatedAt / etc. title stars …. uuid createdAt / updatedAt / etc. title plot …. uuid createdAt / updatedAt / etc. name dob ….

Inheritance

Inheritance User Rating Movie Actor name dob …. title stars …. title plot …. name dob …. Entity uuid createdAt / updatedAt / etc.

Inheritance User Rating Movie Actor name dob …. title stars …. title plot …. name dob …. Entity uuid createdAt / updatedAt / etc.

Inheritance User Rating Movie Actor name dob …. title stars …. title plot …. …. Entity …. Person uuid

Inheritance User Rating Movie Actor name dob …. title stars …. title plot …. …. Entity …. Person uuid

Inheritance Entity User Movie Rating Person Actor

Inheritance Entity User Movie Rating Person Actor

Inheritance Entity User Movie Rating Person Actor

Inheritance Entity User Movie Rating Person Actor

Inheritance Entity User Movie Rating Person Actor

Inheritance Entity User Movie Rating Person Actor

Actor Entity uuid createdAt title actors Movie

Lombok Actor @ToString class Movie Entity uuid createdAt title actors Movie

Lombok Actor @ToString class Movie Entity uuid createdAt title actors Movie Movie(title=The Matrix, actors=[Actor(internationalActive=true)])

Lombok Actor @ToString(callSuper = true) class Movie Entity uuid createdAt title actors Movie Movie(super= Entity(uuid=c1e3c57e-...-b73147a13bfa, createdAt=2023-09-05T10:26:31.305), title=The Matrix, actors=[Actor(dob=1982-03-14,name=Your next Superstar,internationalActive=true,...)])

User Movie Actor Rating

User Movie Actor Rating

Lombok Actor @ToString(callSuper = true) class Movie Entity uuid createdAt title actors Movie Exception in thread "main" java.lang.StackOverflowError at java.lang.AbstractStringBuilder.append(AbstractStringBuilde r.java:449) at java.lang.StringBuilder.append(StringBuilder.java:141) at com.example.domain.Entity.toString(Entity.java:11) at com.example.domain.Movie.toString(Movie.java:11) at java.lang.String.valueOf(String.java:2994) at java.lang.StringBuilder.append(StringBuilder.java:136) at java.util.AbstractCollection.toString(AbstractCollection.ja va:462) at java.lang.String.valueOf(String.java:2994) at

Entity User Movie Rating Person Actor

Lombok Jackson Mapping

Jackson Actor new ObjectMapper() .writeValueAsString(movie) Entity uuid createdAt title actors Movie Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: java.util.ArrayList[0]->com.example.domain.Movie["actors"]- >java.util.ArrayList[0]->com.example.domain.Actor["movies"] ->java.util.ArrayList[0]->com.example.domain.Movie["actors" ]->java.util.ArrayList[0]->com.example.domain.Actor["movies "]->java.util.ArrayList[0]->com.example.domain.Movie["actor s"]->java.util.ArrayList[0]->com.example.domain.Actor["movi es"]->java.util.ArrayList[0]->com.example.domain.Movie["act ors"]->java.util.ArrayList[0]->com.example.domain.Actor["mo vies"]->java.util.ArrayList[0]->com.example.domain.Movie["a ctors"]->java.util.ArrayList[0]->com.example.domain.Actor[" movies"]->java.util.ArrayList[0]->com.example.domain.Movie[ "actors"]->java.util.ArrayList[0]->com.example.domain.Actor

Jackson Actor class Actor { @JsonIgnore public List movies; } Entity uuid createdAt title actors Movie {"uuid":"xxxx", "createdAt":[2023,9,5,11,0,58,264000000], "title":"The Matrix", "actors":[{"uuid":"yyyy", "createdAt":[2023,9,5,11,0,58,265000000], "name":"Your next Superstar", "dob":"1982-03-14", "internationalActive":true} ] }

Jackson Actor class Actor { @JsonIgnoreProperties("actors") public List movies; } Entity uuid createdAt title actors Movie {"uuid":"xxxx", "createdAt":[2023,9,5,11,2,8,999000000], "title":"The Matrix", "actors":[{"uuid":"yyyy", "createdAt":[2023,9,5,11,2,9,1000000], "name":"Your next Superstar", "dob":"1982-03-14", "internationalActive":true, "movies":[{"uuid":"xxxx", "createdAt":[2023,9,5,11,2,8,999000000], "title":"The Matrix"} ] } ] }

User Movie Actor Rating

Data loading (e.g. JPA) User data

Data loading (e.g. JPA) User data Rating data and Movie data OneToMany Ratings

Data loading (e.g. JPA) User data Rating data Movie data OneToMany(fetch = FetchType.EAGER) Ratings

Data loading (e.g. JPA) User data Rating data Movie data OneToMany Ratings @Entity @NamedEntityGraph(name = "User.ratings", attributeNodes = @NamedAttributeNode("ratings") ) public class User { //... }

Data loading (e.g. JPA) User data Rating data Movie data OneToMany Ratings @Entity @NamedEntityGraph(name = "User.ratings", attributeNodes = @NamedAttributeNode("ratings") ) public class User { //... } @Repository public interface UserRepository extends JpaRepository { @EntityGraph(value = "User.ratings") User findEagerById(String id); }

Data loading (e.g. JPA) User data Rating data Movie data OneToMany Ratings @Repository public interface UserRepository extends JpaRepository { @EntityGraph(attributePaths = {"ratings"}) User findEagerById(String id); }

Data loading ● Model your domain to cover all data needed ● Read and understand the specifications of your persistence mapper ● Use built-in mechanisms to load the data for your use-case ● Don’t try to work against the mapper library ○ Use lower abstractions or drivers

Writing readable code public List getValue(Movie m) { String x = "|"; return m.getRelated().stream() .map(a -> { String v1 = a.getValue1(); String v2 = a.getValue2(); return v1 + x + v2; }) .collect(Collectors.toList()); }

Writing readable code public List getValue(Movie movie) { String fieldSeparator = "|"; return movie.getActors().stream() .map(actor -> { String actorName = actor.getName(); String actorDob = actor.getDob(); return actorName + fieldSeparator + actorDob; }) .collect(Collectors.toList()); }

Writing readable code: Be explicit public void setTimeout(int timeout);

Writing readable code: Be explicit public void setTimeout(int timeout[In]Seconds);

Writing readable code: Avoid Utils-classes public class DomainUtils { public static Movie createMovieWithDefaults() { return new Movie( UUID.randomUUID().toString(), "", LocalDateTime.now()); } public static List top5Movies(List movies) { return movies.stream() .sorted((movie1, movie2) -> movie2.getAverageRating().compareTo(movie1.getAverageRating())) .limit(5) .collect(Collectors.toList()); } }

Writing readable code: Avoid Utils-classes public class Movie { public static Movie createDefault() { return new Movie( UUID.randomUUID().toString(), "", LocalDateTime.now()); } }

Writing readable code: Avoid Utils-classes public class Movies { public static List top5Movies(List movies) { return movies.stream() .sorted((movie1, movie2) -> movie2.getAverageRating().compareTo(movie1.getAverageRating())) .limit(5) .collect(Collectors.toList()); } }

Writing readable code: Nesting / Extraction public void update(Movie movie) throws Exception { if (!movie.hasMetadata()) { HttpResponse httpResponse = HttpClientBuilder.create().build().execute(new HttpGet("METADATA_URL")); switch (httpResponse.getStatusLine().getStatusCode()) { case 200: BufferedReader responseReader = new BufferedReader(new InputStreamReader(httpResponse.getEntity().getContent())); String response = responseReader.lines().collect(Collectors.joining()); // movie.set... // default } } if (!movie.hasImage()) { HttpResponse httpResponse = HttpClientBuilder.create().build().execute(new HttpGet("IMAGE_URL")); switch (httpResponse.getStatusLine().getStatusCode()) { case 200: BufferedReader responseReader = new BufferedReader(new InputStreamReader(httpResponse.getEntity().getContent())); String response = responseReader.lines().collect(Collectors.joining()); // movie.setImage(...) // default } }

public void update(Movie movie) throws Exception { if (!movie.hasMetadata()) { updateMetadata(); } if (!movie.hasImage()) { updateImage(); } } Writing readable code: Nesting / Extraction

Writing readable code: Inversion public String getOldestActor(Movie movie) { String oldestActorName; List actors = movie.getActors(); if (actors != null) { Actor oldestActor = actors.stream() .sorted(Comparator.comparing(Person::getDob)) .findFirst().get(); oldestActorName = oldestActor.getName(); } else { oldestActorName = ""; } return oldestActorName; }

Writing readable code: Inversion public String getOldestActor(Movie movie) { List actors = movie.getActors(); if (actors == null) { return ""; } Actor oldestActor = actors.stream() .sorted(Comparator.comparing(Person::getDob)) .findFirst().get(); return oldestActor.getName(); }

Meta

Have friendly exception messages ● Answer some questions ○ How did “we” get here? ○ How can “we” mitigate the situation? ■ Documentation/GH-Issues ● Be empathetic ● You can still be technical ○ What information is needed to support the customer ● Don’t be too verbose ● NEVER throw “expected” exceptions

Create a good documentation ● Have a dedicated technical writer ○ Implicit testing of your application and the documentation state ● Give the documentation to new team members ○ Helps with onboarding and also shows lacks in the documentation ● (if possible) share link to the open source repository ○ Problems/misunderstandings can be filed as issues ○ Customers and users can create PRs

Control and communicate your architecture ● ArchUnit ● API Guardian @API(status = API.Status.STABLE/INTERNAL) ● jQAssistant

Yes, you can use Optional

Yes, you can use Optional, If you are not doing real time big data processing

RTFM

No seriously, RTFM again

RTFM again

Thanks