200 posts tagged with "Errors"

ERROR 1146 (42S02): Table '…' doesn't exist usually means exactly that. But sometimes the table is right there, just with different capital letters, and MySQL on Linux treats Products and products as two different names. This post shows the failing query, the setting that causes it, and how to choose table names that work the same on Linux, Windows and macOS.

ERROR 1264 (22003): Out of range value for column means the number you're saving doesn't fit the column's type. For a DECIMAL column, the limit isn't the number of decimals, which MySQL quietly rounds, but the number of digits before the decimal point. This post finds a column's exact limit, shows the difference between a value that's rounded and one that's refused, and fixes it from both sides: the column and the input.

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails means you inserted or updated a row that points at a parent which doesn't exist. I got it from my own mistake: I guessed that a new category had Id 3, because it was the third one I'd created. It wasn't. This post shows why the guess was wrong, how to find the right Id, how to insert without guessing, and how to answer 400 Bad Request from a .NET C# API.

ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails means the row you're deleting is still in use: another table points at it through a foreign key, and that foreign key forbids the delete. The message even tells you which table and column. This post reads it piece by piece, finds the rows that block the delete, shows two ways to clear them, and turns the error into a 409 Conflict in a .NET C# API.

ERROR 1062 (23000): Duplicate entry … for key … means a unique index refused a value that already exists. Usually that's the index doing its job. The surprise in my case was which value counted as a duplicate: MySQL refused adapters because Adapters was already there. This post explains why, how to choose the behaviour you want, and how to handle the error cleanly in MySQL and in a .NET C# API.

MySQL enforces CHECK constraints, and it tells you when a row breaks one: ERROR 3819 (HY000): Check constraint '…' is violated. I met it twice in one afternoon: first when an EF Core migration tried to add constraints to a table that already held a bad row, then when a new row broke the rule. Both have the same cause and the same kind of fix, and in a .NET C# API the error can become a clear 400 Bad Request instead of a crash.

An EF Core migration script made with dotnet ef migrations script --idempotent failed in MySQL 9.7 at line 8 with ERROR 1064 (42000). Oracle's EF Core provider for MySQL writes the script's "skip what's already applied" checks as SQL Server-style IF NOT EXISTS(…) BEGIN … END blocks, and MySQL accepts that kind of block only inside stored procedures and other stored programs. The fix is a plain script that starts at the database's last applied migration.

The first build of a brand-new .NET 10 Web API failed with error CA1852 on the template's own WeatherForecast record. The solution turns on Microsoft's recommended code-quality rules and treats warnings as errors, and one of those rules asks for types like this one to be sealed. Adding that one word fixes it.

dotnet restore said Restore succeeded, with one warning: Unable to find a project to restore!. Nothing had been restored. I had run it in a folder whose solution file didn't list any projects yet, so that's what it restored: nothing. Pointing it at the project, or adding the project to the solution first, fixes it.

I created an ASP.NET Core Web API project inside a .NET 10 solution that manages package versions centrally, and the template's own restore failed with error NU1008. The template writes a package version into the project file, which central package management doesn't allow. Moving that one version to Directory.Packages.props fixes it.