How to Create
a Fluent API DSL
with Lambda Builders ?

Introduction

LesFurets service orchestration

LesFurets service orchestration

Insurers partners

We have 100 live insurers, on 5 products, each with business validation rules, that filter prospects based on their profile

Insurer exclusions

Hierarchy of 492 legacy classes, no governance or auditability

Use case: insurer exclusions

Insurer exclusions based on object model (legacy code)

                
public void check(FieldContext context, FormuleMoto formule, Conducteur conducteur,
                  Vehicule vehicule, Void unused, Besoins besoins,
                  Set<EAbTestingScenario> scenarios)
                  throws ExclusionException {
    if (besoins == null) {
        return;
    }
    if (besoins.getDateDebutContrat() == null) {
        return;
    }
    if (!DateHelper.isAfter(besoins.getDateDebutContrat(),
                    DateHelper.ajouteJoursADate(DateHelper.getToday(), NBR_JOURS),
                    DateHelper.EPrecision.jour)) {
        throw new ExclusionException(DATE_EFFET_PLUS_60_JOURS);
    }
}

Use case: goal

  • compliance: the rules correspond to the specification documents
  • auditability: understand a rule without looking at the code
  • governance: maintenance of the rules catalogue
  • clarity: productivity for developers

Same rule, more fluent:

                
public ExclusionRule exclusionRule() {
    return DOOV.when(dateContrat().after(todayPlusDays(60)))
               .exclusionRule();
}

Why a fluent API?

Java is verbose, but you can reduce the noise and write code like natural language with a fluent API

                
// SQL query with jOOQ
DSL.using(conn)
        .selectFrom(SALES)
        .where(MODULE.equal(module.getIntValue()))
        .and(NOTIF_DATETIME.greaterOrEqual(from))
        .and(DELETED.equal(SaleState.NO.getIntValue()))
        .stream()
        .map(SalesDAO::toSale)
        .collect(toList());

Meet dOOv!

Domain Object Oriented Validation

dOOv is a fluent API for typesafe domain model validation

dOOv : Under the hood

                
DOOV.when(accountCompany.eq(Company.LES_FURETS)
            .and(accountPhoneNumber.startsWith("+33"))).validate();

Live code

                
public static boolean validateAccount(User user,
                Account account, Configuration config) {
  if (config == null) {
      return false;
  }
  if (user == null || user.getBirthDate() == null) {
      return false;
  }
  if (account == null || account.getCountry() == null ||
      account.getPhoneNumber() == null) {
      return false;
  }
  if (YEARS.between(user.getBirthDate(), LocalDate.now()) >= 18
          && account.getEmail().length() <= config.getMaxEmailSize()
          && account.getCompany() == Company.LES_FURETS
          && account.getPhoneNumber().startsWith("+33")) {
      return true;
  }
  return false;
}
                
              
                
public static SampleModel sample() {
  User user = new User();
  user.setId(1);
  user.setFirstName("Foo");
  user.setLastName("BAR");
  // ...
            
  Account account = new Account();
  account.setCompany(Company.LES_FURETS);
  account.setId(9);
  // ...
                
              
                
public class Account extends Identity {

  @SamplePath(field = SampleFieldId.LOGIN, readable = "account.login")
  private String login;     
  // ...

  @SamplePath(field = SampleFieldId.COMPANY, readable = "account.company")
  private Company company;
  // ...
                
              
                
SampleModelResourceBundle_en_US.properties

account.login = account login
account.password = account password
account.country = account country
account.company = account company
...

SampleModelResourceBundle_fr_FR.properties

account.login = l'identifiant de connection
account.country = le pays
account.company = la soci\u00e9t\u00e9
...

                
              
                
> ./gradlew -p sample build

BUILD SUCCESSFUL in 23s
10 actionable tasks: 3 executed, 7 up-to-date
                
              
                
public class RulesCodeOneTest {
  SampleModelRule demoRule = DslSampleModel
          .when(DOOV.matchAll(
                  userBirthdate.ageAt(today()).greaterOrEquals(18),
                  accountEmail.length().lesserOrEquals(configurationMaxEmailSize),
                  accountCompany.eq(Company.LES_FURETS),
                  accountPhoneNumber.startsWith("+33")))
          .validate();
}
                
              
                
@Test
public void test_account() {
    SampleModel sample = SampleModels.sample();
              
    Result result = demoRule.executeOn(sample);
              
    Assertions.assertThat(result).isTrue();
    System.out.println(demoRule.readable());
    System.out.println(demoRule.markdown(Locale.FRANCE));
}
                
              
                
rule when match all [user birthdate age at today >= 18, //
  account email length is <= configuration max email size, //
  account company = LES_FURETS, account phone number starts with '+33'] validate
* règle
  * lorsque
    * correspond à tous
      * la date de naissance âge à la date du jour >= 18
      * l'émail a une longueur <= la taille maximum de l'émail
      * la société = LES_FURETS
      * le numéro de téléphone commence par '+33'
  * valider
                
              
                
@Test
public void test_account_failure_cause() {
    SampleModel sample = SampleModels.sample();
    sample.getAccount().setPhoneNumber("+1 12 34 56 78");
              
    Result result = demoRule.executeOn(sample);
              
    Assertions.assertThat(result).isTrue();
}
                
              
                
java.lang.AssertionError: Expected result to be true 
  (invalidated nodes: [account phone number starts with '+33'])
                
              
                
@Test
public void test_account_failure_cause() {
    SampleModel sample = SampleModels.sample();
    sample.getAccount().setPhoneNumber("+1 12 34 56 78");
              
    Result result = demoRule.executeOn(sample);
              
    Assertions.assertThat(result)
            .isFalse()
            .hasFailureCause("account phone number starts with '+33'");
}
                
              
                
@Test
public void test_account_failure_cause_2() {
    SampleModel sample = SampleModels.sample();
    sample.getAccount().setPhoneNumber("+1 12 34 56 78");
    sample.getAccount().setCompany(Company.BLABLACAR);
              
    Result result = demoRule.withShortCircuit(false).executeOn(sample);
              
    Assertions.assertThat(result)
            .isFalse()
            .hasFailureCause("match all [account company = LES_FURETS, " +
                    "account phone number starts with '+33']");
}

A few predicate reductions examples

Multiple 'and' operator

Validate that a profile
has an email with less than 20 characters
has at least 18 years when their country is France
their country is France when their phone number starts with '+33' 

                  
  DOOV.when(accountEmail.length().lesserThan(20)
        .and(userBirthdate.ageAt(today()).greaterThan(18)
          .and(accountCountry.eq(Country.FR)))
        .and(accountCountry.eq(Country.FR)
          .and(accountPhoneNumber.startsWith("+33"))))
      .validate();

Multiple 'and' operators

                  
  model.getAccount().setEmail("test@test.org");
  model.getAccount().setCountry(Country.FR);
  model.getUser().setBirthDate(LocalDate.now().minusYears(19));
  
  ValidationRule rule = DOOV
      .when(accountEmail.length().lesserThan(20)  
        .and(userBirthdate.ageAt(today()).greaterThan(18)
            .and(accountCountry.eq(Country.FR)))
        .and(accountCountry.eq(Country.FR)
            .and(accountPhoneNumber.startsWith("+33"))))
      .validate();
  
  Result result = rule.withShortCircuit(false).executeOn(wrapper);
  System.out.println("> " + result.getFailureCause());
                  
                

                  
  > account phone number starts with '+33'

'count' operator for predicates

Validate that a profile match at least two conditions :

  • profile has at least 18 years
  • country is France
  • phone number starts with '+33'

                  
  DOOV.when(count(
        userBirthdate.ageAt(today()).greaterThan(18),
        accountCountry.eq(Country.FR),
        accountPhoneNumber.startsWith("+33")).greaterThan(1))
      .validate();

'count' operator for predicates

                  
  model.getUser().setBirthDate(LocalDate.now().minusYears(19));
  model.getAccount().setCountry(Country.CAN);
  model.getAccount().setPhoneNumber("1 23 45 67 89");
  
  ValidationRule rule = DOOV
      .when(count(
              userBirthdate.ageAt(today()).greaterThan(18),
              accountCountry.eq(Country.FR),
              accountPhoneNumber.startsWith("+33"))
          .greaterThan(1))
      .validate();
  
  Result result = rule.withShortCircuit(false).executeOn(wrapper);
  System.out.println("> " + result.getFailureCause());
                  
                

                  
  > account country = FR and account phone number starts with '+33'

Beyond bean validation

Annotation based APIs for validating POJOs

Bean Validation 2.0 : JSR 380
Reference implementation : Hibernate Validator

Beyond Bean Validation: types

Bean Validation rules are not strongly typed since it's annotation based. This code will fail at compile time, but your IDE won't be able to tell you why.

                
public class Account {

    @NotNull @Email
    private Email email;

}

Beyond Bean Validation: complex validation

Because Bean Validation constraints are based on field annotation, cross validation between fields are only available through the extension mechanism.

                
public class Account {

    @Pattern(regexp = "(FR)|(UK)")
    private String country;

    @Pattern(regexp = "???")
    private String phoneNumber;

}

Beyond Bean Validation: natural language

Bean Validation rules are not written with a natural language syntax and does not provide a syntax tree

                
@Size(min = 10, max = 200,
      message = "About Me must be between 10 and 200 characters")
private String aboutMe;

DSL

                
userAboutMe().length().between(10, 200).validate().readable()
> When user about me length is between 10 and 200, validate

Beyond Bean Validation: syntax versus consistency

 

Bean Validation allows syntax validation
 
 
Bean Validation rules are written on the model
 
 
Bean Validation uses reflection
dOOv allows consistency checks
 
 
dOOv rules are writtent outside of the model, allowing complex checks
 
 
dOOv uses code generation

Going further

LesFurets service Mapping

Domain Object Oriented Mapping

Next step is extending the DSL to create a
bean mapping framework

It features the same AST to text and statistics functionalities.

Use Case : Object-to-Object Mapping

source model 

                    
class Model {
  User user;
  Account account;
}

class User {
  String firstName;
  String lastName;
  LocalDate birthdate;
}

class Account {
  String email;
  boolean acceptEmail;
  Country country;
}

→

target model 

                    
class Employee {
  String fullName;
  String email;
  int age;
  String country;
  String company;
}

Use Case : Object-to-Object Mapping

                      Model model = ...;
Employee employee = new Employee();
// declarative mapping rule
MappingRule rules = mappings(
  when(accountAcceptEmail.isTrue())
      .then(map(accountEmail).to(employeeEmail)),

  map(userFirstName, userLastName)
      .using(biConverter((f, l) -> f + " " + l, "", "combine names"))
      .to(employeeFullname),

  map(userBirthdate.ageAt(today())).to(employeeAge),

  map(accountCountry)
      .using(converter(c -> c.name(), "country name"))
      .to(employeeCountry)
);
// then execute the mapping
rules.executeOn(model, employee)

Use Case : Object-to-Object Mapping

                      Model model = ...;
Employee employee = new Employee();
// declarative mapping rule
MappingRule rules = mappings(
  when(accountAcceptEmail.isTrue())
      .then(map(accountEmail).to(employeeEmail)),

  map(userFirstName, userLastName)
      .using(biConverter(
            (f, l) -> f + " " + l, "", "combine names"))
      .to(employeeFullname),

  map(userBirthdate.ageAt(today())).to(employeeAge),

  map(accountCountry)
      .using(converter(c -> c.name(), "country name"))
      .to(employeeCountry)
);
// then execute the mapping
rules.executeOn(model, employee)

Use Case : Object-to-Object Mapping

                      Model model = ...;
Employee employee = new Employee();
// declarative mapping rule
MappingRule rules = mappings(
  when(accountAcceptEmail.isTrue())
      .then(map(accountEmail).to(employeeEmail)),

  map(userFirstName, userLastName)
      .using(biConverter(
            (f, l) -> f + " " + l, "", "combine names"))
      .to(employeeFullname),

  map(userBirthdate.ageAt(today())).to(employeeAge),

  map(accountCountry)
      .using(converter(c -> c.name(), "country name"))
      .to(employeeCountry)
);
// then execute the mapping
rules.executeOn(model, employee)

Use Case : Object Manipulation

                
MappingRule rules = mappings(
  when(employeeAge.lesserThan(18))
      .then(mapNull(employeeFullname)),
  map(employeeEmail)
      .using(converter(s -> sha256.hashString(s), "sha256 string"))
      .to(employeeEmail)
)
// then execute the mapping
.executeOn(employee, employee)

We migrated our 492 business rules to dOOv,
we now have compliance, auditability, governance, clarity
and more!

Enjoy dOOv.org

http://www.dOOv.org