.NET Framework and Core for Application Development
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In ASP.NET Core you ask for a DbContext, and one appears. Which one? Each HTTP request gets its own, shared by everything in that request, and it's disposed of when the request ends. This guide proves that with real IDs, and explains what the rule means for code that lives outside a request.
When a unique index refuses a value, EF Core throws an exception, and your API answers 500. But nothing broke: the client asked for something that already exists, and 409 Conflict is the right answer. This guide reads MySQL's error number from the exception, and catches only that error, with a small helper you can reuse.
When two people edit the same row, the second save overwrites the first, and nobody finds out. A concurrency token fixes this: a column that changes with every update, and that EF Core adds to the WHERE of each UPDATE. If it changed since you read the row, the update finds nothing, and you can tell the client. This guide adds one on MySQL.
Clients want to choose a list's sort order, as in ?sort=-price. It's tempting to pass that text through to the query, but a query string should never decide which columns your database sorts on. An allow-list and a C# switch give clients the choice, and keep the control in your code.
A list endpoint usually has optional filters: a category, a search term, a checkbox. Since an EF Core query doesn't run until the end, you can add each Where only when its filter is present, and get SQL with exactly those conditions. This guide builds that, and shows the SQL for different requests.
EF Core gives you several ways to search text, and on MySQL with Oracle's provider they behave differently in ways that matter: some ignore case, some don't, and one treats % as a wildcard. This guide runs each one on the same data, and reads the SQL, so you can choose.
A list endpoint shouldn't return every row. Skip and Take give you one page at a time, which EF Core turns into MySQL's LIMIT and OFFSET. Getting it right takes three more things: a sort order rows can't escape from, the total count, and a limit on the page size. This guide builds all of it.
ExecuteDeleteAsync sends one DELETE to MySQL, without loading anything, for one row or thousands. It's shorter than loading a row and removing it. But its errors arrive differently, and that catches people out. This guide shows the call, the SQL, and how to handle a foreign key refusal.
SaveChangesAsync loads rows, changes them in memory and writes them back. When you already know the change, that's wasted effort. ExecuteUpdateAsync sends one UPDATE straight to MySQL, for one row or thousands. This guide shows it in use, reads the SQL, and demonstrates the two ways it can surprise you.
To delete a row with EF Core, load it, call Remove, and call SaveChangesAsync. A Web API also needs to answer the two things that can go wrong: the row isn't there, and other rows still depend on it. This guide does all of that, with the real SQL from MySQL.
