EF Core - Error CS1503 Argument 2: cannot convert from 'string' to 'System.FormattableString'

I was pair programming with a team member when she got the following compiler error:

Error CS1503 Argument 2: cannot convert from 'string' to 'System.FormattableString'

The error appeared after trying to compile the following code:

	var ids = context.Database
	.SqlQuery<int>("SELECT TOP 10 ProductId FROM Products")
	.ToList();

view raw GetProductIds.cs hosted with ❤ by GitHub

The reason becomes apparent when we look at the signature of the SqlQuery method:

As you can see the method expects a FormattableString not a string. Why is this?

By using a FormattableString EF Core can protect us from SQL injection attacks. When we use this query with parameters(through string interpolation), the supplied parameters values are wrapped in a DbParameter.

To get rid of the compiler error, we can do 2 things:

1. We explicitly create  a FormattableString from a regular string:

	var ids = context.Database
	.SqlQuery<int>(FormattableStringFactory.Create("SELECT TOP 10 ProductId FROM Products"))
	.ToList();

view raw GetProductIds.cs hosted with ❤ by GitHub

2. We use string interpolation and add a ‘$’ sign in front of the query string:

	var ids = context.Database
	.SqlQuery<int>($"SELECT TOP 10 ProductId FROM Products")
	.ToList();

view raw GetProductIds.cs hosted with ❤ by GitHub

More information

SQL Queries - EF Core | Microsoft Learn

RelationalDatabaseFacadeExtensions.SqlQuery<TResult> Method (Microsoft.EntityFrameworkCore) | Microsoft Learn