Common mistakes

The most common mistakes when using DI, configuration, and logging are collected in Table 6.4.

Table 6.4. Common mistakes in dependency injection, configuration, and logging

Problem	Cause	Fix
`Unable to resolve service for type …`	the dependency is not registered, or a different type is registered (a class instead of an interface)	add `Add…<IService, Impl>()`; `ValidateOnBuild`
`Cannot consume scoped service … from singleton`	a Scoped service in a Singleton's constructor	align the lifetimes or use `IServiceScopeFactory`
a value from `appsettings.json` is not read	the file was not copied to the output folder, a typo in the key	`CopyToOutputDirectory`; the options pattern
Development settings do not apply after running the `.exe`	`launchSettings.json` is read only by VS and `dotnet run`	set `DOTNET_ENVIRONMENT`
a password ended up in the repository	the secret was written to `appsettings.json`	user secrets, environment variables; change the password
log entries without fields, slow performance	`$"…"` interpolation instead of a template	a `{Name}` template or `[LoggerMessage]`

Common mistakes ​