Building Your Data Layer: Creating Entities, Migrations, and Adding References in .NET Core

We will learn how we can add a new entity in a .net project and update it into a database using migration.

In this we are going to create product entity

Before creating an entity we can create a product controller which is not necessary to learn to add a new entity but we can learn adding full api for Product entity.

Code example

Other methods will be created in a similar way shown in above image.

Lets Create an entity now

We are going to keep everything into the entity folder, for a better structure we can add a DAL layer and add our code there.

We will also learn about Repository patterns so we can access common methods of databases from that.

After move our DbContext to database layer, it start showing references errors, lets resolve it by adding references(Dependencies) to DAL layer

Right click on dependencies, it will show options

There are multiple ways to add references in the project

1 option will add reference to a project. If we choose this we can add an ESTORE project into that and that project contains all the necessary dependencies that need to be added to the DAL layer. Lets try this option

Now all there error resolve in the DbContext file

Do the same for Migration Folder , let's move it to DAL layer from ESTORE

All errors are resolved now, because DAL has ESTOREContext (DbContext class)

Now we have some reference issues in the Program.cs file because it is looking for DbContext Reference which does not exist in the ESTORE project, now we can do one thing which is Add Reference of DAL to ESTORE but it will create circular dependencies. Because ESTORE is already added in DAL. So better is to isolate DAL from ESTORE, we can remove ESTORE from DAL and Add required dependencies to DAL layer.

When I try to add DAL in the ESTORE Project it does not add it.

Lets remove ESTORE from DAL

Now add DAL project into ESTORE

Now its allow to add this DAL project in ESTORE, lets add required dependencies in DAL for DbContext(Identity)

We can search package on nuget website

After a package is found click on it to see commands to install

This is dotnet command (vscode) . We can use package manager or install dependencies using visual studio nuget feature.

We can add these using package reference , double click on project name , then you can see xml file add this line their

So our DAL layer needs these Package References, we already have these in ESTORE so we can copy and paste it in DAL project xml file

DAL xml files after adding References

So after adding these Packages References, Build the Project

No more Reference Errors there now

Now Resolve Program.cs REF errors

Click on the error word so the mouse cursor will be moved there after that press CTRL + DOT (ctrl .) cmd it will show solution to fix errors, just like image we have add the name (ref) of the file

All errors fixed

Let's build the project and run the project to see its working

Its working fine without any issue, so we are learned how to Add Layer and how to fix References errors in PROJECT, also we should not try to add Circular dependencies

It is call CODE FIRST APPROACH

Create Product class in DAL’s Entities folder.

We included Data annotation with properties of class.

Next Step is Register this Product entity class in DbContext Class

Error

Fix: make it public

Now let's create a Migration for Product table.

Open PMC

Code generated by Migration CMD

Now lets update our database

Product Table Updated successfully , Let's confirm it on SSMS

It's added.

So this is how we can add tables using CODE first approach. (using migration)

In the DB first approach we first add tables in the database directly and then Scaffold the database in the project using CMD in the package manager console.

Lets Create Repository To access data

The Repository Pattern is a design pattern that provides an abstraction layer between the data access layer and the business logic layer of an application. This pattern helps to isolate data access logic and business logic, making the code more maintainable and testable.

Let's create Base Repository

Add Method signatures in IRepository.cs and Implement this Interface in Repository, these class and interface will treated as base class and it is generic class which accept T type as class

Create generic IRepository Interface and add necessary method’s signatures

Now Create generic Repository Class and Implement IRepository Interface

So we have completed our Repository Service and whenever we want to create an Entity Repository we have to implement this Repository with a newly created Entity Repository. In our case It ProductRepository

To Provide it as Dependency To other class we have to create IProductRepository Interface

Let's Create IProductRepository and Implement IRepository interface

Now create ProductRepository and implement Repository class and IProductRepository interface

Now our ProductRepository is ready to use but we have to register our dependencies in Program.cs file first

Then we can use it.

Lets Register Dependencies

We register both Services(repositories)

They have register in different way

Generic Repository registration is a little bit different than others. We are passing typeof(.. ) as params

So now we can use our ProductRepository. We are going to do this in ProductController. We can create a Business Layer for better architecture and manage our business logic there and can inject Repositories there.

Let's do it with ProductController