Fixes for Common Issues and Errors
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An INSERT into MySQL stopped with ERROR 1364 (HY000): Field 'CreatedAtUtc' doesn't have a default value. The column needs a value, the statement didn't give one, and MySQL has nothing to fall back on. The fix is to send the value, or give the column a default.
I sent a product price of 9.999 to my API, and it answered 201 Created with a price of 10.00. No error, no warning: MySQL rounded the amount to fit its DECIMAL(12,2) column, even in strict mode, and raised only a note that EF Core never shows. For money, silently changing the number isn't acceptable, so the API now refuses it.
A long category name made my API answer 500, with Data too long for column 'Name' at row 1 in the log. MySQL was right to refuse it: the column is varchar(100), and the name had 101 characters. The problem was that the request got as far as MySQL at all. A validation attribute stops it first, and the client gets an answer it can act on.
Right after I added a property to an EF Core entity, every request that touched that table answered 500, and the log said MySqlException: Unknown column 'p.Version' in 'field list'. The code built without a problem, because the C# was fine. The table simply didn't have that column yet: changing the class doesn't change the database until a migration does.
A check on this site refused two blog posts with front matter does not parse, and then missed comma between flow collection entries. Every line in those lists ended with a comma. The problem was a # in one post and [] in the other. Both mean something to YAML, even inside a list of plain words.
A Python script stopped with ModuleNotFoundError: No module named 'PIL'. The obvious fix, pip install PIL, fails as well, because the package isn't called that: you import PIL, and you install Pillow. Here's how the error came up, what the failing fix looks like, and the install that works.
ImageMagick's montage stopped with montage: unable to read font, and the contact sheet it left behind had no labels. This Homebrew build of ImageMagick has no list of fonts, so it had nothing to draw the labels with. Naming a font file with -font, before the images, fixes it.
Unable to create a 'DbContext' of type 'Dewiride.Inventory.Data.InventoryDbContext'. The exception 'Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions`1[Dewiride.Inventory.Data.InventoryDbContext]' while attempting to activate 'Dewiride.Inventory.Data.InventoryDbContext'.' was thrown while attempting to create an instance. The useful part is the line printed just before it: the app's own startup code had failed, so EF Core's tools couldn't get the DbContext the normal way. Here's how I ran into it with a migrations bundle, why --connection didn't help, and the fix.
NU1608: Detected package version outside of dependency constraint: Pomelo.EntityFrameworkCore.MySql 9.0.0 requires Microsoft.EntityFrameworkCore.Relational (>= 9.0.0 && <= 9.0.999) but version Microsoft.EntityFrameworkCore.Relational 10.0.14 was resolved. The message spells out the problem: the newest Pomelo MySQL provider is built for EF Core 9, and the project runs EF Core 10. That isn't a version to nudge; it's a provider that doesn't support your EF Core yet.
dotnet package update --vulnerable is .NET 10's way to move vulnerable packages to a fixed version in one command. In my solution it printed error: Restore failed, then Unhandled exception: Specified method is not supported., and stopped. The crash message is misleading; the cause is documented: the command restores to do its work, and TreatWarningsAsErrors turned NuGet's own vulnerability warning into a restore error.
