Hi all,
Coming from a Java background, I am having a hard time understanding how
validation error propagation should work in clojure web APIs.
To be clear, this is similar to how my Java web service would be setup:
/** Method that validates the model, accesses the DB. If something went
wrong, throw an exception */
public void validateAndCreateUser(User u) throws ValidationException,
EmailAlreadyInUseException, ... {
...
if(...) {
throw new ValidationException(fieldName);
} else if (...) {
throw new EmailAlreadyInUseException(u.getEmail());
}
}
/** Endpoint method, catches & formats the exceptions thrown by the db
method. **/
@POST("/api/user/create")
public Response createUser (User u) {
..
try{
validateAndCreateUser(u);
return Response.ok();
} catch (Exception e) {
return generateExceptionResponse(e); //Method that maps exceptions to
responses.
}
}
For all of Java's clunkiness, this had the benefit of not having to write
tons of if/else statements for validation handling. Exception were just
thrown from anywhere, bubbling back up to inital call, and if not handled
in the endpoint method, a specialized class mapped them into a proper
response. The exceptions contained all the information needed to generate
'rich' error messages back to the client.
Being a Clojure newbie, I wonder what a good pattern is for a similar
situation. So far, I have a method that validates models based on a schema,
that returns
{:success true}
or
{:success false :errors ["error 1" "error 2" ...]}
But I don't know how to avoid having to write if/else conditions of the
sort in each function between my endpoint and db functions.
(if (validation :success)
(follow-normal-path)
(handle-validation-errors validation))
Any guidance appreciated.
Cheers,
Julien
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