Common Errors and Troubleshooting in Programming
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Changing a MySQL setting failed with ERROR 1227 (42000): Access denied; you need (at least one of) the SUPER or SYSTEM_VARIABLES_ADMIN privilege(s) for this operation. The word GLOBAL in the statement is the cause. Most of the time you don't want the whole server changed anyway, and one word fixes it.
I wanted to see which transactions were open, and MySQL said ERROR 1227 (42000): Access denied; you need (at least one of) the PROCESS privilege(s) for this operation. The account has full rights on its own database, and that's not enough. Here's why, and the right way to fix it without making your application's account more powerful.
An UPDATE hung for a while, then failed with ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction. Raising the timeout is the tempting fix, and the wrong one, because the real problem is another transaction holding the row. Here's how to find it, and a surprise about what the error leaves behind.
An ordinary UPDATE failed with ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction, and MySQL threw away everything the transaction had done so far. Two transactions had taken the same rows in opposite orders. Here's how to see that for yourself, and the small change that stops it.
Before .NET 10, minimal APIs didn't check data annotations: you needed a filter or a library. Now one line in Program.cs does it. Put [Required] and [Range] on your request record, and a bad request gets a 400 with every problem listed, before your handler runs. This guide adds it, with the same requests before and after.
Out of the box, an ASP.NET Core API's errors are all different: an empty 404, a stack trace as plain text in Development, and a blank 500 in Production. Problem details is the standard JSON format for errors, and three lines in Program.cs give every failure that one shape. This guide adds them, with the real responses before and after.
After I added one small GET endpoint, every request to my minimal API answered 500, health checks included. The log said Body was inferred but the method does not allow inferred body parameters. The endpoint took a record as a parameter, and ASP.NET Core assumes that comes from the JSON body, which GET doesn't get. [AsParameters] tells it to read the query string instead.
I wanted to read something from the database once, while the app started, so I asked app.Services for the DbContext in Program.cs. The app crashed: Cannot resolve scoped service 'Dewiride.Inventory.Data.InventoryDbContext' from root provider. Scoped services need a scope, and at startup there's no request to provide one. You can create one yourself in two lines.
My API refused to start: Cannot consume scoped service 'Microsoft.EntityFrameworkCore.DbContextOptions1[…InventoryDbContext]' from singleton 'Dewiride.Inventory.Api.CategoryCache'.A small cache class, registered as a singleton, asked for theDbContext. A singleton lives as long as the app, and a DbContextbelongs to one request, so ASP.NET Core stops it.IServiceScopeFactory` is the way for a singleton to use one.
A POST with perfectly good JSON came back as 415 Unsupported Media Type, and the API's log had nothing to say about it. The JSON wasn't the problem: the request never said it was JSON. curl labels a -d body as a web form unless you tell it otherwise, and a minimal API endpoint that expects JSON won't touch that.
