For a long time, I've been thinking about how to design a data visualization library that would make it easier to compose charts from simple components. On the one hand, there are charting libraries like Google Charts, which offer a long list of pre-defined charts. On the other hand, there are libraries like D3.js, which let you construct any data visualization, but in a very low-level way. There is also Vega, based the idea of grammar of graphics, which is somewhere in between, but requires you to specify[...]

I had been working on a client project where I built the GraphQL backend for a new social network using primarily AppSync, Lambda and DynamoDB. One of the features of the app was to support private messaging between two users. To allow either user to fetch their chat messages in chronological descending order, I modelled … AppSync: how to compare strings lexicographically in VTL Read More » Liked this article? Support me on Patreon and get direct help from me via a private Slack channel or 1-2-1 mentori[...]

Hi, welcome to another weekly update. Production-Ready Serverless workshop goes virtual! Starting from May 4th, I will be running a 4-week instructor-led workshop that teaches you everything you need to know to build a production-ready serverless application. It’s based on the same demo app as my Manning course, but all the code has been completely … Weekly update 44 Read More » Liked this article? Support me on Patreon and get direct help from me via a private Slack channel or 1-2-1 mentoring. Hi,[...]

Most real-world programming languages are too complex to be studied using formal methods. For this reason, academics often work with simple theoretical languages instead. The λ-calculus is a simple formal language that is often used for talking about functional languages, the π-calculus is a model of concurrent programming and there is an entire book, A Theory of Objects modelling various object-oriented systems. Animation from Financial Times article "Why the world's recycling system stopped working". Tho[...]

TL;DR To make an AppSync DynamoDB resolver throw exceptions on conditional check errors, we need to check $context.error in the response mapping template ourselves. Like this: #if ( $ctx.error ) #if ( $ctx.error.type.equals("DynamoDB:ConditionalCheckFailedException") ) $util.error("your error message") #else $util.error($ctx.error.message, $ctx.error.type) #end #end $utils.toJson($context.result) And now, the longer version. The problem AppSync lets us perform DynamoDB … AppSync: how to error on DynamoDB[...]