Common mistakes

Common mistakes

Common mistakes when working with EF Core are listed in Table 8.3.

Table 8.3. Common mistakes when working with EF Core

Problem	Cause	Fix
changes do not appear in the database	SaveChangesAsync was forgotten	save after changes; check the result
Npgsql…: Failed to connect to 127.0.0.1:5432	the server is not running, the wrong port or connection string	start the PostgreSQL service; check the secrets
relation "Products" does not exist	the migration has not been applied	dotnet ef database update
a slow program, hundreds of queries in the log	N+1 queries: accessing a relationship in a loop	Include or a Select projection
the whole table is read from the database	ToList()/AsEnumerable() before Where	filter in IQueryable before ToListAsync
could not be translated	a custom C# method in the query condition	rewrite the condition or evaluate it on the client after filtering
an exception for DateTime in timestamp with time zone	DateTime.Now has Kind = Local	DateTime.UtcNow
A second operation was started on this context	a shared context for parallel operations	a separate context or a factory
a cycle during JSON serialization	the Author.Posts and Post.Author navigations refer to each other	serialize a DTO projection
a migration drops a column with data	a property was renamed	review the migration and replace it with RenameColumn