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

ExplainMe

ExplainMe.

So I have 4 "project" inside:

ExplainMe

ExplainMe

ExplainMe

ExplainMe (controllers),

ExplainMe.Core

ExplainMe.Core

ExplainMe.Core

ExplainMe.Core (currently empty),

ExplainMe.Data

ExplainMe.Data

ExplainMe.Data

ExplainMe.Data (entities),

ExplainMe.EF

ExplainMe.EF

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

url/api/user?name=john

url/api/user?name=john

Create
```
UserController
```
UserController
```
UserController
```
UserController
inside
```
ExplainMe.Controllers
```
ExplainMe.Controllers
```
ExplainMe.Controllers
```
ExplainMe.Controllers
.
Create
```
UserService
```
UserService
```
UserService
```
UserService
inside
```
ExplainMe.Core.Services
```
ExplainMe.Core.Services
```
ExplainMe.Core.Services
```
ExplainMe.Core.Services
(i assume?).
what now? Which class am I missing and where? somewhere should probably be
```
IUserService
```
IUserService
```
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 EFEF and a DataData project, data probably only contains the entities. I'd usually call that

Domain

Domain

myself

Pobiega•10/8/24, 1:45 PM

the EFEF 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 _myDbContextprivate 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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