Repository which layer

When you receive a command in a command handler, you use repositories to get the data you want to update from the database. You update it in memory with the data passed with the commands, and you then add or update the data domain entities in the database through a transaction. It's important to emphasize again that you should only define one repository for each aggregate root, as shown in Figure To achieve the goal of the aggregate root to maintain transactional consistency between all the objects within the aggregate, you should never create a repository for each table in the database.

Figure The relationship between repositories, aggregates, and database tables. The above diagram shows the relationships between Domain and Infrastructure layers: Buyer Aggregate depends on the IBuyerRepository and Order Aggregate depends on the IOrderRepository interfaces, these interfaces are implemented in the Infrastructure layer by the corresponding repositories that depend on UnitOfWork, also implemented there, that accesses the tables in the Data tier.

It can be valuable to implement your repository design in such a way that it enforces the rule that only aggregate roots should have repositories. You can create a generic or base repository type that constrains the type of entities it works with to ensure they have the IAggregateRoot marker interface. Thus, each repository class implemented at the infrastructure layer implements its own contract or interface, as shown in the following code:.

However, a better way to have the code enforce the convention that each repository is related to a single aggregate is to implement a generic repository type. That way, it's explicit that you're using a repository to target a specific aggregate. That can be easily done by implementing a generic IRepository base interface, as in the following code:. The Repository pattern allows you to easily test your application with unit tests.

Remember that unit tests only test your code, not infrastructure, so the repository abstractions make it easier to achieve that goal. As noted in an earlier section, it's recommended that you define and place the repository interfaces in the domain model layer so the application layer, such as your Web API microservice, doesn't depend directly on the infrastructure layer where you've implemented the actual repository classes.

By doing this and using Dependency Injection in the controllers of your Web API, you can implement mock repositories that return fake data instead of data from the database. This decoupled approach allows you to create and run unit tests that focus the logic of your application without requiring connectivity to the database.

Connections to databases can fail and, more importantly, running hundreds of tests against a database is bad for two reasons. First, it can take a long time because of the large number of tests. Second, the database records might change and impact the results of your tests, so that they might not be consistent.

Testing against the database isn't a unit test but an integration test. The answer to this is also given by Microsoft. Microsoft themselves recommend using Repository Patterns in complex scenarios to reduce the coupling and provide better Testability of your solutions. In cases where you want the simplest possible code, you would want to avoid the Repository Pattern. But i strongly advice to not use Design Patterns everywhere. Try to use it only whenever the scenario demands the usage of a Design Pattern.

That being stated, Repository pattern is something that can benefit you in the long run. What seperates this guide from the others is that we will also be working with a Clean Architecture in mind to demonstrate the real-life implementation.

This means that we will be working with multiple Layers and Projects and also go through the basics of Dependency Inversion Principle. Read this article to install this awesome IDE on to your machine.

Here I am naming my Solution as RepositoryPattern. We will call it DataAccess. EFCore and Domain. Here are the features and purposes of each project. Create a new Folder in the Domain Project named Entities. Next , we will setup and configure Entity Framework Core. Install these Required Packages in the DataAccess. EFCore Project.

Add a reference to the Domain Project where we have defined our entities and create a new Class in the DataAccess. NET Core Application. We will also update the database in this step to accomadate the Developer and Project Table.

Firstly, Install this package on the WebApi Project. Next, Navigate to Startup. Note that you will have to add a refernce of the DataAccess.

Here is a screenshot. Ps, This is a very basic setup of Entity Framework Core. Give it a look to learn more.

Traditionally, you would directly call the dbContext object to read and write data. This is fine. But is it really ideal for the long run? When you use the dbContext directly, what you are doing is that, the Entity Framework Core is being tightly coupled within your application. So, Tommorow when there is something newer and better than EFCore, you would find it really annoying to implement the new tech and make the corresponding changes.

One more disadvantage of directly using the dbContext directly is that you would be exposing the DbContext, which is totally insecure.

Yet we write it multiple times over and over. Because, we will be inverting the dependencies, so that, you can define the interface in the Domain Project, but the implementation can be outside the Domain Project.

In this case, the implementations will go the DataAccess. This is a simple explanation of Dependency Inversion Principle. Pretty Cool, yeah? Here T is the specific class.

The set of functions depends on your preference. Ideally, we require 7 functions that cover most of the data handling part. Create a new class in the DataAccess. This class will implement the IGenericRepository Interface. We will also inject the ApplicationContext here.

This way we are hiding all the actions related to the dbContext object within Repository Classes. This is not something to be done in a Repository Class.

We would need Unit of Work Pattern for these cases where you commit data to the database. We will discuss about Unit of Work in a later section. When there are large number of entites in our application, we would need seperate repositories for each entities. But we do not want to implement all of the above 7 Functions in each and every Repository Class, right?

Thus we made a generic repository that holds the most commonly used implementaions. Now what happens if we need the records of Most Popular Developers from our Database? We do not have a function for it in our Generic Class, do we? This is where we can see the advantage of building a Generic Repository.

Get it? You can notice that we have not implemented all the 7 functions here, as it is is already implemented in our Generic Repository.

Saves a lot of lines, yeah? You can see that the interface and implementations are quite blank. So why create new class and interface for Project? This can also attribute to a good practice while developing applications. We also anticipate that in future, there can be functions that are spcific to the Project Entity. To support them later on, we provide with interfaces and classes. Future Proofing, yeah? Navigate to Startup.

Unit of Work Pattern is a design pattern with which you can expose various respostiories in our application. It has very similar properties of dbContext, just that Unit of Work is not coupled to any framework like dbContext to Entity Framework Core. Till now, we have built a couple of repositories. We can easily inject these repositories to the constructor of the Services classes and access data. Another Ouch!

Usually a repository is used as scaffolding to populate your entities - a service layer would go out and source a request. It is likely that you would put a repository under your service layer. Repository layer is implemented to access the database and helps to extend the CRUD operations on the database. Whereas a service layer consists of the business logic of the application and may use the repository layer to implement certain logic involving the database.

In an application, it is better to have a separate repository layer and service layer. Having separate repository and service layers make the code more modular and decouple the database from business logic. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Difference between Repository and Service Layer?

Ask Question. Asked 10 years, 8 months ago. Active 3 years, 1 month ago. Viewed k times. Improve this question. Sam Sam Add a comment. Active Oldest Votes. Repository Layer gives you additional level of abstraction over data access.

Repository layer exposes basic CRUD operations. Service layer exposes business logic, which uses repository. In ASP. Get id. Improve this answer. StepUp This is better achieved within the repository, where it can be the default behavior of the List method, or the List method might be renamed to something like ListActive.

Repositories that follow the advice of not exposing IQueryable can often become bloated with many custom query methods. The solution to this is to separate queries into their own types, using the Specification Design Pattern.

The specification can include the expression used to filter the query, any parameters associated with this expression, as well as how much data the query should return i. Combining the Repository and Specification patterns can be a great way to ensure you follow the Single Responsibility Principle in your data access code. See an example of how to implement a generic repository along with a generic specification in C.

Introducing The CachedRepository Pattern. Building a CachedRepository via Strategy Pattern. Repository Pattern Repository Pattern The Repository Pattern has gained quite a bit of popularity since it was first introduced as a part of Domain-Driven Design in Specification If you're considering implementing the Repository pattern in your.

Repository Per Entity or Business Object The simplest approach, especially with an existing system, is to create a new Repository implementation for each business object you need to store to or retrieve from your persistence layer.

Generic Repository Interface Another approach is to go ahead and create a simple, generic interface for your Repository. T GetById int id ;. Find id ;.