Dot Net What Not Posts

I’m not under any illusions that anyone actually reads this blog, I mainly use it as a place to keep my discoveries, as I have a lousy memory, and would never be able to find them otherwise! A case in point was a data query I was asked to do this afternoon. A project’s database includes a table of users, and a table of countries, with a joining table to specify which users are responsible for which countries (this is a many-to-many relationship for reasons that are not relevant to this post). The client wanted a spreadsheet where each row contained one country. This sounded similar in structure to a query I did some time ago, where I discovered an overload of the Linq SelectMany method that I had never used before. Sadly, I had not blogged about it, so couldn’t find the notes. Not making that mistake again, so…

With a couple of recent projects, I have been using Azure DevOps instead of my usual SVN for source control. This uses Git, and whilst the mind migration to Git has been generally painless, there have been a couple of points that keep tripping me up. One of these is convincing Git that the .gitignore file has changed. When you start a new project in Visual Studio, and use Team Explorer to connect to Azure DevOps, it automatically adds everything to Git, including the bin and obj folders. You generally don’t want to put these under source control. No problem, crack up the .gitignore file and add the following lines… Visual Studio sometimes creates this for you, but even if it does, you still need to modify manually if you add a new project, as it doesn’t seem to do that for you. So, you confidently hit the refresh button…

We use the rather excellent mailTrap for testing code that sends emails. Whilst this site is very well done, I didn’t realise quite how clever the developers were until I noticed this…

One of our main applications involves interacting with a third-party API. Whilst this is generally stable, we have had cases recently where it was throwing random exceptions. We could make the same request with the same parameters multiple times, and sometimes it would work, and sometimes it wouldn’t.

While we left the owners of the third-party API scratching their heads, we realised that the way we handled interaction with such APIs wasn’t robust enough. The first (and most obvious) improvement would simply be to try again.

As this is the sort of thing we’d want to do in a number of places, rather than repeat the same boilerplate code over and over again, we looked for a helper class.

Being fairly new with EF Core, I am still discovering solutions to problems that I solved long ago with database-first development.

Today I found out how to add a non-nullable foreign key reference to a new table.

We had a situation in which application users were not checking the customer list before adding new customers, which was resulting in multiple entries for the same customer. We wanted to make it so that when they tried to add a new customer, they would be shown a list of possible duplicates.

It turned out that finding duplicates wasn’t as easy as I thought. I ended up with a helper class that used Metaphones to find similar customers. This post describes the class, and shows how to use it.

I was working with a third-party API, and had to specify a date range object, with a start and date. The problem was, their server was throwing intermittent exceptions when I passed this date filter object as a parameter, claiming that the start date was after the end date. I checked the data, and I was definitely sending a valid date range.

The answer to the problem turned out to involve a little-known (to me at least) part of DateTime. Not the sort of thing you encounter every day, but worth knowing about for the times when it hits you.

I had an odd problem, the resolution of which exposed an interesting bit of information about what goes on under the C# covers that we never usually know.

I had a Linq query that worked fine on its own, but failed at run time when I extracted it into a method and passed in a lambda.

Whilst trying to work out why this was happening, I came to an understanding of the difference between a Func and an Expression, and why it (sometimes) matters.