C#•15mo ago

Multilayer architecture - explanation?

tl;dr: Have been mostly working on existing projects and have some problems in early stages of the architecture development.

Hey all!
I would need some additional explanation on how do you usually approach the multilayer architecture. I came across one early project which already had some of the projects made, but idk why and what should even be there (lets call this project

ExplainMe

ExplainMe

.

So I have 4 "project" inside:

ExplainMe

ExplainMe

(controllers),

ExplainMe.Core

ExplainMe.Core

(currently empty),

ExplainMe.Data

ExplainMe.Data

(entities),

ExplainMe.EF

ExplainMe.EF

dbContext..

Lets say I would like to implement an API request

url/api/user?name=john

url/api/user?name=john

Create

UserController

UserController

inside

ExplainMe.Controllers

ExplainMe.Controllers

Create

UserService

UserService

inside

ExplainMe.Core.Services

ExplainMe.Core.Services

(i assume?).

what now? Which class am I missing and where? somewhere should probably be
```
IUserService
```
```
IUserService
```
, but where?

Pobiega•10/8/24, 1:13 PM

yes
yes
Yeah you would use an interface to make testing easier. This would be defined in either the Core project near the service most likely.

PPobiega - yes - yes - Yeah you would use an interface to make testing easier. This would...

reeeeeeeOP•10/8/24, 1:40 PM

are IUserService and UserService both in Core project?
how would GetUserByName method look like? Should it get data from EF project or Data? Is Data only entities/models or is there any processing, etc?

Pobiega•10/8/24, 1:44 PM

Yeah, both in core. The interface only serves the purpose of allowing mocking in tests really.
Your service would probably have a DbContext be injected, or have a wrapper in the form of a repository. Its generally recommended NOT to use repositories over EF for various reasons thou, but its still pretty common in especially n-layer apps

Pobiega•10/8/24, 1:45 PM

If you have both an

EF

EF

and a

Data

Data

project, data probably only contains the entities. I'd usually call that

Domain

Domain

myself

Pobiega•10/8/24, 1:45 PM

the

EF

EF

project contains the context, the configurations and migrations, I assume

PPobiega the `EF` project contains the context, the configurations and migrations, I as...

reeeeeeeOP•10/8/24, 2:33 PM

thats right

PPobiega If you have both an `EF` and a `Data` project, data probably only contains the e...

reeeeeeeOP•10/8/24, 2:34 PM

yeah i always have some doubts about naming properly, lol

PPobiega Yeah, both in core. The interface only serves the purpose of allowing mocking in...

reeeeeeeOP•10/8/24, 2:35 PM

Aha, ok. so User service would have something like this:

private DbContext _myDbContext

private DbContext _myDbContext

GetUserByName(stirng name) => _myDbContext.Users.FirstOrDefault(x => x.Name == name);

GetUserByName(stirng name) => _myDbContext.Users.FirstOrDefault(x => x.Name == name);

Pobiega•10/8/24, 2:36 PM

Yup

Pobiega•10/8/24, 2:36 PM

But async etc ;p

PPobiega But async etc ;p

reeeeeeeOP•10/8/24, 2:37 PM

yeye ofc

PPobiega But async etc ;p

reeeeeeeOP•10/8/24, 2:38 PM

i previously watched some tutories/guides which connected Controller - Service - repository - context, and I just could figure it out why would you pass the stuff so many times

reeeeeeeOP•10/8/24, 2:40 PM

anyway thanks for your help

Pobiega•10/8/24, 2:59 PM

So the answer to that is... Complicated

Pobiega•10/8/24, 2:59 PM

You could obviously do the query directly in the controller

Pobiega•10/8/24, 2:59 PM

But now your controller is aware of your database, mixing data with http

Pobiega•10/8/24, 3:00 PM

Since introduce. Level of abstraction, the service. This lets us separate the work from the http stuff

Pobiega•10/8/24, 3:00 PM

Ok but what if we want to change database? Now we have to rewrite all our services, that might or might not use the datavase

Pobiega•10/8/24, 3:01 PM

So we move all dB access to its own thing, the repository

Pobiega•10/8/24, 3:02 PM

But the repository itself can't communicate with the database, that's what the context does. So we implement the repo using the context.

Pobiega•10/8/24, 3:02 PM

That's the reason. Is it s good reason? Many would disagree

Pobiega•10/8/24, 3:03 PM

Look at things like FastEndpoints, or Immediate handlers/ImmediateApi

Multilayer architecture - explanation?

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