C#•3y ago

❔ ✅ Why am I getting error message CS0184?

I am trying to compare the return type of a generic method, which produces the following warning. How does the IDE knows my delegate will never be of that certain return type?

Jimmacle•11/9/23, 8:49 PM

because what that code is doing is checking if an instance of

Type

Type

is an instance of

int

int

which will never be true

Jimmacle•11/9/23, 8:50 PM

you're looking for something like

func.Method.ReturnType.IsAssignableTo(typeof(int))

func.Method.ReturnType.IsAssignableTo(typeof(int))

acaOP•11/9/23, 8:51 PM

Could I switch the

func.Method.ReturnType

func.Method.ReturnType

and handle casewise for certain datatypes?

Jimmacle•11/9/23, 8:51 PM

no, because types aren't constants

TeBeCo•11/9/23, 8:52 PM

once you're in

System.Type

System.Type

world ... you're not linked anymore to the value of these variable

TeBeCo•11/9/23, 8:52 PM

you can't use actual types and generic anymore

TeBeCo•11/9/23, 8:53 PM

also that

is

is

would need compare an actual returned value if you're doing an

is int

is int

i assume not a type

TeBeCo•11/9/23, 8:53 PM

ie: checking the type of a value vs checking if a type is a subtype of

Jimmacle•11/9/23, 8:53 PM

also as an aside that

using (Con)

using (Con)

looks suspicious, do you intend for this method to dispose of a connection it doesn't "own"?

TeBeCo•11/9/23, 8:54 PM

even the

_cmd = new SqlCommand()

_cmd = new SqlCommand()

acaOP•11/9/23, 8:54 PM

I have the Con defined as my SqlConnection for the class and I am applying methods for handling CRUD functionality

Jimmacle•11/9/23, 8:54 PM

right, so if you call this you will dispose your sql connection and it won't work for any future calls

TeBeCo•11/9/23, 8:55 PM

is there a reason here not to use Dapper or EFCore out of curiosity ?

acaOP•11/9/23, 8:55 PM

I am still a newbie and my teacher also said usually this isn't how pushing into a SQL database is done, but it will has to do for now since I don't know any other way unfortunately

acaOP•11/9/23, 8:56 PM

Basically I am handling CRUD by opening, executing the SQL and closing the connection in many smaller methods

TeBeCo•11/9/23, 8:56 PM

ok fair enough if you're learn

acaOP•11/9/23, 8:56 PM

And I tried to create a generic method accepting a delegate since I either insert a SqlCommand or SqlBulkCopy

TeBeCo•11/9/23, 8:57 PM

this level of manually handling lower ADO.NET primitive is just something that's usually never done anymore
(it's fine ot learn what's under the hood at least once)

acaOP•11/9/23, 8:57 PM

Was this how it was done earlier?

TeBeCo•11/9/23, 8:57 PM

like in 2003/2005 yeah

acaOP•11/9/23, 8:58 PM

I have background in engineering so my logic is quite developed and I found this to be the most logical way of doing it with my knowledge so far

Jimmacle•11/9/23, 8:58 PM

the next level up in terms of abstraction would be using a library like dapper, then even more abstract would be ef core

TeBeCo•11/9/23, 8:58 PM

up to probably 2010/2013-2015 maybe but that's it

acaOP•11/9/23, 8:58 PM

Makes sense, I just always try to make my methods generic which sometimes isn't working in my favour sadly

Aaca I have background in engineering so my logic is quite developed and I found this...

TeBeCo•11/9/23, 8:59 PM

so imagine you're a company like Stackoverflow or Microsoft

TeBeCo•11/9/23, 8:59 PM

and you see millions / billions C# dev

TeBeCo•11/9/23, 8:59 PM

doing again and again that same code

TeBeCo•11/9/23, 8:59 PM

can you create code to avoid them doing it them self and ~70% of the time wrong

TeBeCo•11/9/23, 8:59 PM

and thus get a more robust abstraction so they just focus on query => result

TeBeCo•11/9/23, 9:00 PM

that's when Dapper comes in place

Jimmacle•11/9/23, 9:00 PM

for example, i have this query using EF core and there is 0 actual SQL involved

TeBeCo•11/9/23, 9:00 PM

and EFCore is when you when the tooling to even do the DB creation + possible manipulation of scheme, and versionning, from C# and not from SQL Schema

TeBeCo•11/9/23, 9:01 PM

so what you're doing is 100% fine so that you don't get a magic thing running, you understand the primitives

TeBeCo•11/9/23, 9:01 PM

in the long run you'll generally move on Dapper or EFcore

acaOP•11/9/23, 9:01 PM

I can recognize some LINQ - we have just starting delving into the topic. So basically nowadays one wants to avoid SQL, which is why LINQ is there (to encapsulate queries?)

TeBeCo•11/9/23, 9:02 PM

it look like Linq it's similar but at the same time not really

TeBeCo•11/9/23, 9:02 PM

it's the same syntax

Jimmacle•11/9/23, 9:02 PM

you still want to understand the SQL, but libraries like EF core have the advantage of providing compile time safety to your queries by writing them in C# against C# models using linq

TeBeCo•11/9/23, 9:02 PM

and it's translated to SQL when you tell it to evalute that "Expression" + tell it to execute it

Jimmacle•11/9/23, 9:03 PM

yeah, that screenshot is technically 2 queries that are composed of some common setup

Jimmacle•11/9/23, 9:03 PM

no sql is generated until one of the

await

await

ed methods is called

Jimmacle•11/9/23, 9:03 PM

then EF core will take that linq expression and figure out what the SQL query should be based on your model

Jimmacle•11/9/23, 9:04 PM

then send it and convert the response to whatever object type you asked for

Jimmacle•11/9/23, 9:06 PM

compared to something like dapper, where you still hand-write the SQL query but it can handle mapping objects to and from C# for you

acaOP•11/9/23, 9:06 PM

I see - the subject is a bit out of scope for me, but I can understand a large part of it. It seems I just need to be able to put all information regarding the certain topic into a collective understanding