Hey Is there any good pattern for this use case I have an AP

Question

Hey Is there any good pattern for this use case I have an API that returns an `Employee` for instance I want it to have non null values for a lot of fields which actually are nullable in the underlying system So I would like to have my client deserialize the API response into a `User` and then use a `toEmployee` method that returns a `ValidatedNel lt Problem Employee gt ` More in thread

Emil Kantis · Answer

My `Employee` class looks like ```data class Employee val id UInt val firstName String val lastName String val workEmail String val supervisorId UInt val ssn String val teamId UInt val teamName String val personalEmail String val phone String val bankClearingNumber String val bankAccountNumber String val taxationTable UInt val address String val zipCode String val city String val employmentAgreements List lt EmploymentAgreement gt val children List lt Child gt SerialName salary val salaries List lt Salary gt ``` but it turns out everything but id is nullable so the `User` class looks like ``` Serializable data class User val id UInt val firstName String val lastName String val workEmail String val supervisorId UInt val ssn String val teamId UInt val teamName String val personalEmail String val phone String val bankClearingNumber String val bankAccountNumber String val taxationTable UInt val address String val zipCode String val city String val employmentAgreements List lt EmploymentAgreement gt val children List lt Child gt SerialName salary val salaries List lt Salary gt fun toEmployee ValidatedNel lt Exception Employee gt = TODO ```

Emil Kantis · Answer

Zipping everything field by field feels very tedious slightly smiling face

simon.vergauwen · Answer

gt Zipping everything field by field feels very tedious You can probably write some more generic for your use case using `memberProperties` <https kotlinlang org api latest jvm stdlib kotlin reflect full member properties html> Something that iterates over all properties and validates them while collecting the `Invalid` If the resulting `List lt Invalid gt ` is empty then you can construct the `Valid` case

simon.vergauwen · Answer

It s not something that exists in Arrow and probably shouldn t but could work well for your use case If you don t need this pattern a lot I would just opt for the bit of `zip` boilerplate It s what I typically see as the necessary evil to be precise and total in all my functions

stojan · Answer

Another alternative is to not write a dto and write a converter instead <https github com uberto kondor json|https github com uberto kondor json>

Emil Kantis · Answer

I suppose I could do that I m already using kotlinx serialization everywhere though but I guess the pattern can be used there as well

Emil Kantis · Answer

Thanks guys I think I ll try out both approaches and see how it ends up looking slightly smiling face

Emil Kantis · Answer

< simon vergauwen> wont I run into issues with zipping due to too many properties IIRC those methods have a max of 14 params or something

simon.vergauwen · Answer

They indeed have a limit but you can easily compose them further by using an intermediate tuple ```validatedA zip validatedJ zip validatedK validatedL Triple a b c d e f g h i j k l gt ```

Emil Kantis · Answer

Was hoping to use the constructor ref guess that wont be doable disappointed Running into lots of duplication of the names Aside from that I think this is working quite nicely slightly smiling face ```fun EmployeeDTO validated ValidatedNel lt String Employee gt val validatedFirstName = fromNullable firstName Missing first name toValidatedNel val validatedLastName = fromNullable lastName Missing last name toValidatedNel val validatedEmail = fromNullable workEmail personalEmail Missing email toValidatedNel val validSsn = fromNullable ssn Missing SSN toValidatedNel val validBankClearingNumber = fromNullable bankClearingNumber Missing bank clearing number toValidatedNel val validBankAccountNumber = fromNullable bankAccountNumber Missing bank account number toValidatedNel val validTaxationTable = fromNullable taxationTable Missing taxation table toValidatedNel val agreements = employmentAgreements map it validated sequence return id validNel zip validatedFirstName validatedLastName validatedEmail supervisorId validNel validSsn phone validNel validBankClearingNumber validBankAccountNumber validTaxationTable agreements children validNel salaries validNel Employee ```

Emil Kantis · Answer

Suppose I can wrap some of the data into some other data class though since it s split from the response model of the API now

simon.vergauwen · Answer

gt Was hoping to use the constructor ref guess that wont be doable You can easily do this if you define a `zip` method with the same arity as the constructor Let s say a `data class` with `12` properties Granted it s rather boilerplate y but also why we choose to limit to 9 params Otherwise it becomes really bloated in Arrow Core ```fun lt E A B C D E F G H I J K L M gt Validated lt E A gt zip validatedB Validated lt E B gt validatedC Validated lt E C gt = zip validatedJ zip validatedK validatedL Triple a b c d e f g h i j k l gt ```