Press "Enter" to skip to content

Category: Misc Languages

Polymorphism in GraphQL

Published 2020-10-12 by Kevin Feasel

Dan Freeman takes us through the concept of polymorphism as it applies to GraphQL:

In APIs (and in domain modeling in general) it’s common to want to represent fields that may point to one (or more) of several different types of object, a.k.a. polymorphism. In GraphQL’s type system, this can be accomplished with either a union or an interface, depending on whether the objects in question are expected to have anything in common.

What’s not always obvious to newcomers to GraphQL, though, is how to best handle that data on the receiving end, when you need to tell what concrete type of object you’re dealing with.

It’s interesting to see how this is handled in GraphQL versus object-oriented languages.

Comments closed

Configuration Advice for Using EF Core with Azure SQL DB

Published 2020-09-24 by Kevin Feasel

Erik Ejlskov Jensen has some advice if you’re using Entity Framework Core with Azure SQL Databases:

If you are connecting from .NET Framework with EF Core 2.x, use .NET 4.6.2 or later. If there are connection errors with this version or newer, the client will retry immediately, and handle transient connection errors gracefully.

If you are using EF Core 3.x, update to 3.1.7 or newer to take advantage of bug fixes in the Microsoft.Data.SqlClient dependency, that has been updated to version 1.1.3. For older EF Core versions, you can opt-in to a newer version (ever 2.0.0 or higher) as described in my blog post.

If you are using EF Core 5, you get the version 2.0.1. Microsoft.Data.SqlClient, which includes advanced Azure Active Directory authentication options.

Click through for more tips, including how to set up automated retry of commands.

Comments closed

Fun with Scala

Published 2020-09-21 by Kevin Feasel

Muskan Gupta has started a series on common mistakes in Scala. Part 1 has to do with matching:

In the example, we are matching against the single case at a time. But, what if we want to match against multiple cases at a time? How will we do that?

The solution to that is using “|”(pipe) operator.

Let’s consider a scenario where you want to check if the user input is a String or an Int. If it is String or Int then it’s a perfect match else not. Now, I’ll give you the options for how can we do this and you should pick the correct option.

Part 2 involves unpacking a tuple:

Now, what if we don’t want to access the variables in the way shown in the above picture?

The other way could be doing tuple unpacking. In this, we bind every value in the tuple with a variable/reference. This is done using Pattern Matching internally.

Now, we will look at a situation and I’ll give you some options so that we can figure out the correct way of doing tuple unpacking. 

These are short, multiple-choice questions along with the explanation.

Comments closed

Trying Out Redis

Published 2020-09-15 by Kevin Feasel

Paul Brebner walks us through some of the basics of Redis:

It took me sometime to work out what Redis really isn’t, and is!

The Redis documentation says what it is not:

“Redis is not a plain key-value store…”

And what it is:

“It is actually a data structures server, supporting different kinds of values.”

So, it (really) is a fast in-memory key-value store, where keys are always strings, but the value can actually be a number of different data types, with different operations supported on each data type. It’s also distributed (using the cluster mode, and supports replication). And it’s got two types of disk persistence (which makes it more like a database), and a caching mode. See the FAQ for more details.

Redis can be extremely valuable as a cache, though persistent Redis can introduce weird problems at scale.

Comments closed

Building an Azure Function to Automate CHECKDB

Published 2020-09-11 by Kevin Feasel

Arun Sirpal shows us how to build an Azure Function:

The title is a mouthful and so is this post. In the past I have linked to blog posts from Microsoft that say consistency checks for Azure SQL Database is the responsibility of Microsoft. (https://azure.microsoft.com/en-gb/blog/data-integrity-in-azure-sql-database/)

However, Paul Randal got me thinking about his thoughts on it (via his insider email). Forming the core of this post. If you desire to run DBCC CHECKDB against Azure SQL Database (which I know people do) – how can you do this? There are many ways, but for this blog post – Enter Azure functions. There are many moving parts to this, but once setup and coded it is a very satisfying experience. Let’s dig in. I am NOT going to copy and paste every little element of the high-level guide from Microsoft, there is no point in that but I will show you the links that you need to setup the relevant function app project then the tailored bits around CHECKDB forms the bulk of this post.

This isn’t necessary to do, but if you want to learn how Azure Functions work, it’s a good example of working through the mechanics.

Comments closed

Comparing Cassandra and DynamoDB

Published 2020-08-31 by Kevin Feasel

Lewis DiFelice compares and contrasts Cassandra with DynamoDB:

In this post, we’ll look at some of the key differences between Apache Cassandra (hereafter just Cassandra) and DynamoDB.

Both are distributed databases and have similar architecture, and both offer incredible scalability, reliability, and resilience. However, there are also differences,  and understanding the differences and cost benefits can help you determine the right solution for your application.

There’s some good info in this comparison.

Comments closed

Mutation Testing in Action

Published 2020-08-28 by Kevin Feasel

Nathan Thompson walks us through a mutation testing experiment:

Since our hypothesis was that the implementation differences between Jasmine and Jest could affect the Mutation Score of our legacy and new test suites, we began by cataloging every bit of Jasmine-specific syntax in our legacy suite. We then compiled a list of roughly forty test files that we would target for Mutation Testing in order to cover the full syntax catalog. For each file we generated a Mutation Score for its legacy state, converted it to run in our new Jest setup, and generated a Mutation Score again. Our hope was that the new Jest framework would have a Mutation Score as good as or better than our legacy framework.

By limiting the scope of our test to just a few dozen files, we were able to run all mutations Stryker had to offer within a reasonable timeframe. However, the sheer size of our codebase and the sprawling dependency trees in any given feature presented other challenges to this work. As I mentioned before, Stryker copies the source code to be mutated into separate sandbox directories. By default, it copies the entire project into each sandbox, but that was too much for Node.js to handle in our repository:

In my undergrad days, I loved mutation testing mostly because of the terminology. I’m happy to see a proper implementation of mutation testing and I’m even happier to see that they have a .NET version.

Comments closed

Querying Power BI from Visual Studio Code

Published 2020-08-25 by Kevin Feasel

Phil Seamark shows us how to write queries against Power BI using Visual Studio Code:

It’s helpful to understand there are two main client libraries for Analysis Services. A client library is what you can add to any new Visual Studio Code Project to provide objects, methods and functions relevant for the tool you are building.

Make sure you download the NetCore (.Net Core) versions of these libraries when working with Visual Studio Code. There are .Net Framework versions of these libraries that are more suited to use with the full Visual Studio product.

Read on for links to those libraries and a thorough demonstration.

Comments closed

Generating Stored Procedure Mappings for Entity Framework Core

Published 2020-08-24 by Kevin Feasel

Erik Ejlskov Jensen takes us through stored procedure mapping with Entity Framework Core Power Tools:

In my previous post I showed how you can map and use stored procedures manually from EF Core, a process which involved quite a bit of code, and some changes to your derived DbContext.

With the latest release of EF Core Power Tools, you can opt-in to have any SQL Server stored procedures in your database made available to you.

Click through to learn how to do this.

Comments closed

Domain Models: Purity vs Completeness

Published 2020-08-07 by Kevin Feasel

Vladimir Khorikov reflects on domain modeling:

This is an example of a rich domain model: all business rules (also known as domain logic) are located in the domain classes. There’s one such rule currently — that we can only assign to the user an email that belongs to the corporate domain of that user’s company. There’s no way for the client code to bypass this invariant — a hallmark of a highly encapsulated domain model.

We can also say that our domain model is complete. A complete domain model is a model that contains all the application’s domain logic. In other words, there’s no domain logic fragmentation.

Domain logic fragmentation is when the domain logic resides in layers other than the domain layer. In our example, the UserController (which belongs to the application services layer) doesn’t contain any such logic, it serves solely as a coordinator between the domain layer and the database.

Domain modeling doesn’t land on too many database administrators’ doorsteps, but I enjoyed the article.

Comments closed