280 posts tagged with "C#"

EF Core decides what SQL to send by looking at each entity's state. There are five states, and once you know them, SaveChangesAsync stops being mysterious. This guide follows one entity through all of them, printing the state at each step and showing the SQL each save sends.

When SaveChangesAsync does something you didn't expect, or nothing at all, you need to see what EF Core thinks has changed. ChangeTracker.DebugView.LongView prints it: every tracked entity, its state, each property's value, and what changed from what. This guide reads it for a real change.

ToQueryString() gives you the SQL a LINQ query would send, as a string, without running it. It's handy for one query you want to look at, with no need to turn on logging for the whole app. This guide shows it with a constant and a variable.

AnyAsync answers one question: is there at least one row like this? It sends SELECT EXISTS and returns true or false, so nothing gets loaded or counted. This guide shows the call, the SQL, and the one thing it can't do safely.

CountAsync asks MySQL how many rows match, without loading any of them. It's what you need for totals, such as "page 2 of 7". This guide shows its forms and the SQL each one sends.

A product belongs to a category, but a query for products doesn't load the category unless you ask. There are two ways to ask: Include and Select. They both produce a join and differ in how much they load. This guide runs each one on MySQL and reads the SQL, including what happens if you ask for neither.

By default, EF Core remembers every entity a query returns, in case you change it. AsNoTracking turns that off for one query, which saves work when you only want to read. This guide shows what it changes and what it doesn't, measures the difference on 5,000 rows, and explains the cases where you don't need it at all.

When several queries return the same response, you want one definition of how to build it. The obvious way, a normal C# method inside Select, loads every column, and throws NullReferenceException as soon as it touches a navigation. The same code written as an Expression lets EF Core read it, and it sends only the columns and joins it needs.

Reading a whole entity sends every column over the wire, even when you only use two. A Select call tells EF Core which values you want, and it asks MySQL for exactly those. This guide compares the SQL for both, maps the result to a record, and checks what happens to change tracking.

EF Core has three common ways to read one row: FirstOrDefaultAsync, SingleOrDefaultAsync and FindAsync. They look the same on a happy day and differ in what they send to MySQL and when they throw. This guide runs all three on the same row and compares the SQL, so you can pick with evidence.