Skip to main content

Instantiate a type based on json and metadata using lift-json

Image
By User



I would like to deserialise Scala case classes that have been serialised using lift-json. The problem I am having is, I don't know how to invoke the generic method extractOpt[A] method below:







someString:String = {...}

JsonParser.parse(someString).extractOpt[A]







The type of [A] is going to depend on metadata, for example the class name of [A] but for the life of me I can't work out how to make the call using reflection. In c# I would just be able to set the generic type for a call on extractOpt[A] using reflection. I fear my problems are something to do with Java type erasure.






I am going to have a lot of case classes so I really want to avoid having to create some kind of hand crafted map from {metadata} -> classOf[]. I have full control over what the metadata associated with someString is.






If it helps understand why I have this issue, I am implementing event sourcing, and all my [A] types are going to be persisted events. Any ideas what I can do?


Labels:

Comments

  1. Tips For AllFebruary 21, 2012 at 2:17 PM

    val json:JValue = JsonParser.parse(someString)
    //typeName = classCanonicalName, ie this is the metadata
    val eventType = Class.forName(typeName)
    val deserialised:Event = Extraction.extract(json, TypeInfo(eventType,None)).asInstanceOf[Event]


    And for bonus points, why does pressing the 'ask question' button on StackOverflow lead to you instantly being able to think of a solution to your own problem? ;)

    ReplyDelete

Post a Comment

Popular posts from this blog

Why is this Javascript much *slower* than its jQuery equivalent?

By User
I have a HTML list of about 500 items and a "filter" box above it. I started by using jQuery to filter the list when I typed a letter (timing code added later): $('#filter').keyup( function() { var jqStart = (new Date).getTime(); var search = $(this).val().toLowerCase(); var $list = $('ul.ablist > li'); $list.each( function() { if ( $(this).text().toLowerCase().indexOf(search) === -1 ) $(this).hide(); else $(this).show(); } ); console.log('Time: ' + ((new Date).getTime() - jqStart)); } ); However, there was a couple of seconds delay after typing each letter (particularly the first letter). So I thought it may be slightly quicker if I used plain Javascript (I read recently that jQuery's each function is particularly slow). Here's my JS equivalent: document.getElementById('filter').addEventListener( 'keyup', function () { var jsStart = (new Date).getTime()...
3 comments
Read more

Is it possible to have IF statement in an Echo statement in PHP

By User
Thanks in advance. I did look at the other questions/answers that were similar and didn't find exactly what I was looking for. I'm trying to do this, am I on the right path? echo " <div id='tabs-".$match."'> <textarea id='".$match."' name='".$match."'>". if ($COLUMN_NAME === $match) { echo $FIELD_WITH_COLUMN_NAME; } else { } ."</textarea> <script type='text/javascript'> CKEDITOR.replace( '".$match."' ); </script> </div>"; I am getting the following error message in the browser: Parse error: syntax error, unexpected T_IF Please let me know if this is the right way to go about nesting an IF statement inside an echo. Thank you.
5 comments
Read more