I have read many pages regarding repository pattern,tons of them are online and each of them starts with we should use it because it makes the application testable and also separation matters,but i also see many opinions against this pattern,or also they say its depends on the application which approach to take,all in all the thing is implementation of the logic must be kept away from controller,can anyone tell me how can i do it if generic repository is not the first option?im new in entity framework
Related
[Pre]
I have to say that I'm dummy newbie who is trying to get together important puzzles with such crucial details as DDD, TDD, MVVM, and EFCore. I have an about 10 years of windows form develop experience in complete wrong manner, and after I'm joined to Plurasight I'm understood that I'm just lost my last 10 years, and this is really sad :).
[Problem description]
I have an App that i want to re-write from scratch by using latest and greatest technics that've learned for the last 6 month on Pluralsight, but the problem is that these new knowledge’s is stopping me, because simply I'm afraid that I'll do it wrong again...(that is stupid I know, but it is what it is).
So back to my questions, I have a big problem domain, and pretty well documented business logic, which i have to turn in to the code. I'm understand that my start point is design data layer, for these purposes I want to use Entity framework core (I saw Julie Lerman's course on Pluralsight and I think's she is amazing and inspires me to use EFCore as ORM for my app). But at the same time leakage of experience produces more questions than what I’ve learned with Pluralsight, and I will try to write them all(please don’t judge me too hard)
It is looks like that I will need 2 or even more data model projects in my solution, and here is why I have multiple document set types, each of the type contain more than one reference books used to generate unique file names and data sheets. But it looks weird to me have 3 Data model projects such as MyApp.PackType1.DataModel, MyApp.PackType2.DataModel, and each of them will be preinstalled with the EFCore, and each of them will generates its own database based on Data Context defined by EF. Isn’t it very redundant or this is correct way?
I don’t understand how to join these multiple Data Models projects, including Shared Kernel into the one nice model
I don’t understand what is the best way to design my data classes? Should they be just POCO’s or I can design them as nice looking classes with the private var’s and public properties? What are the best practices in here?
Also I don’t understand what is the best practice to use a MVVM pattern on top of that, and is it applicable at all to use MVVM in this case?
Should I keep my Tests in separate projects like MyApp.PackType1.DataModel.Tests, or keep them in same project?
Best regards,
Maks!
P.S.
Apologize for unclear definitions and questions, English isn't my native language.
It's very complicated to answer your question because you have asked for a lot of details, but I going to provide a brief answer and I hope it will be helpful.
You can have only one model for your entities (DDD) and create sub model from this model in your end level projects (Web API or UI)
Read point #1
You have to create an Entity Layer project that represents your database and then you can create DTO's for specific scenarios
From my point of view, use Angular but you can use another UI framework such as React or VueJs, but I prefer to use Angular to build UI interfaces and consume .NET Core Web API from client
Create unit tests and integration tests for you Web API projects and as additional feature you can use Db in memory provider for tests
May be this guide is useful: https://www.codeproject.com/Articles/1160586/Entity-Framework-Core-for-Enterprise
Regards
Hm, multiple DbContexts (models) usually come about when you have distinct databases you are using. General rule is one Context = one Database. Exceptions can occur when there are a lot of tables that can be grouped functionally, but there are downsides to that approach.
A DbContext is a repository pattern but for individual tables. Using a Unit of Work pattern and layering with a custom repository provider would allow you to make it "appear" as a single database, hiding the complexity from the front-end.
Your entity descriptions are usually created as straight POCO. You can get creative with different DTOs
In a nutshell, an MVVM pattern goes like this:
Request from UI to a controller
Controller possibly issues multiple calls to Data Layer to gather data
Assemble data in a single ViewModel (everything the page needs)
Return to UI
The beauty of the approach is single roundtrip (request/response) to the UI
Separate Project in my opinion. There are techniques to spoof the database connection using EF so you are not using "live" data.
That CodeProject article will come in handy.
I am building simple REST deployable using Spring Boot. Decided to create it by using failing acceptance test first followed with TDD until its green.
My module is pretty simple, I have 3 API's:
Retrieving list of data from datastore.
Adds item to datastore.
Deletes item from datastore.
I feel like it is good idea to abstract datastore and have maybe backed by Map data structure for testing purposes and use it with either NoSQL or SQL db if I want to for deployments/releases and end to end testing.
On the service layer side I am unsure since it would just delegate call to repository with no logic.
So standard approach would be controller->service->repository. In my case service does not do much(possible some exception handling but not more) and I will end up with interface and implementation as an extra as well as few more lines of code. I fell like going for controller->repository solution in my situation but it is not a practice I have seen and not sure how others would see it.
What's the best way to implement this sort of system?
I feel like it is good idea to abstract datastore
You are right. The abstraction is called 'Repository' in DDD (Domain Driven Design) for example.
On the service layer side I am unsure since it would just delegate call to repository with no logic.
I'm pretty sure there are data that you want to validate. So you should have a layer in the middle (e.g. the domain layer) which will be in charge of this validation.
Even so, if you feel like your application is simple and doesn't require such layers, go without. You will have less supple design, but more simplicity at first. Be careful: while evolving your app, you could run into trouble.
Hope this will help.
This is rather an opinion based question, but if you are asking whether a 3 layer architecture is a must, to that I say no. Be pragmatic, if you don' see a reason for a class/layer/module to exist, it does not need to exist.
A repository has a purpose (to store/retrieve), and the api layer has a purpose, to offer those things through HTTP.
Here is an article for building small services with the sparkframework: https://dzone.com/articles/building-simple-restful-api
Is it a best practice to implement repository pattern with entity framework 6 (and upper versions)? why? It seems that Microsoft doesn't recommend it!
I think it is a good idea to add repository pattern over entity-framework as it can help you alot in many areas. But it can also add a new layer of complexity. So points to consider are:
Using repository you can limit clients to specific operations. (Can be a pro or con depending on requirements and implementation)
You can also provide ready made functions for complex operations so client don't have to repeats that logic.
Repositories can be made thread safe as DbContext isn't.
Repositories will allow you to be independent of entity framework so in future if you ever need to move away from it you can just changed underlying functionality easily.
You can intercept incoming db operations in repository and do whatever you like with them. e.g. add addition where clause in multi-company scenario.
Testing becomes more easier as it becomes easy to mock underlying functionality.
But Repositories also have others cons.
Look at these Is the Repository pattern useful with Entity Framework?
and Benefit of Unit of Work and Repository Pattern with Entity Framework
Previously I asked this question and on a answer I got this comment:
This works, however injecting the container to a part, as far as I know, is not a "normal" use-case of MEF.
In my web app I have a few repositories that, of course, retrieve entities from the DB. To make them as loosely coupled as possible I'm making them return interfaces (eg IUser, IBill, IBlaBlaBla...) and the repository project only references the library project (that contains the interfaces). I use MEF composition capabilities to tie it all up...
Since the repository must have a concrete object to fill with info it got from the DB and the only the Container is aware of which concrete class maps to a specific interface I think that the repository MUST have reference to the container so it can call the "Resolve()", get a new instance and do his job, but that apparently is a mistake.
Can anyone tell me why and what approach would be better?
PS: I don't know if it's relevant but I'm using DDD...
I think the flaw in your design that lead to this problem is the use of interfaces to hide entities behind. Since entities are your core concept in your domain, there should be no use in hiding them behind an abstraction. Let's put it differently: do you ever have a different implementation of IUser?
In other words, ditch the IUser, IBill, etc. interface and let your repositories and business commands depend directly on your aggregate entities.
i developed an sample application using Entity Framework 4.0. but now i'm gonne developed a real app for a company. where i would like to implement the DAL with Entity framework with generic repository , unit of work and DI container.
please any one suggest me a real example for the framework..
Thanks
Rusho
Generic repository is nonsense. If you want to use design pattern called Repository you should think about specific repository and aggregate roots.
Generic repository is just a wrapper around ObjectSet / DbSet providing no added value - only additional layer which must be maintained and which makes interaction with EF harder. Also adding repository without clarifying why you want to do that and what it should solve for you is wrong approach - design pattern is a blue print for solving a problem. Not something you should use just because it exists and everybody talks about it.
You can also check these answers where I discuss generic repository and its implications:
Generic Repository With EF 4.1 what is the point
The repository itself is not usually tested?