Setup DbContext

Add database provider package

To connect to specific database, you should pick one package to do that. Generally that provider package implicitly installs Microsoft.EntityFrameworkCore.

For example, if you're using MSSQL:

dotnet add package Microsoft.EntityFrameworkCore.SqlServer

or PostgreSQL:

dotnet add package Npgsql.EntityFrameworkCore.PostgreSQL

Inherit from DbContext

The abstraction of rows are usually presented as a DbSet<T> where T must be a class

using Microsoft.EntityFrameworkCore;

public class MoviesContext : DbContext
{
    public DbSet<Movie> Movies { get; set; } // nullable warning goes here
}

While nullable warning may shows here, so you can use DbContext.Set<T>() instead to softly remove the warning.

using Microsoft.EntityFrameworkCore;

public class MoviesContext : DbContext
{
    public DbSet<Movie> Movies => Set<Movie>();
}

INFO

DbSet<T> is IQueryable, so all operations are lazy.

Setup database provider

EFCore needs to know which database engine it'll work with. The provider comes from the certain package you'll need to install. For example, use Microsoft.EntityFrameworkCore.SqlServer if you're working with MSSQL; Use Npgsql.EntityFrameworkCore.PostgreSQL to work with PostgreSQL. There's always a nuget package fits the database you use.

To setup database provider, an virtual empty method DbContext.OnConfiguring exists to do the job.

// source code of DbContext
public class DbContext :
    IInfrastructure<IServiceProvider>,
    IDbContextDependencies,
    IDbSetCache,
    IDbContextPoolable
{
    // ...other memebers
    protected internal virtual void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { } // yes it's empty
}

There'll be an extension method injected from the provier package to the DbContextOptionsBuilder

public class MoviesContext : DbContext
{
    public DbSet<Movie> Movies => Set<Movie>();
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        string connectionString = "...";
        optionsBuilder.UseSqlServer(connectionString); // use MSSQL here
        base.OnConfiguring(optionsBuilder);
    }
}

Injection

Lastly, inject your DbContext.

/* Program.cs */
builder.Services.AddDbContext<MoviesContext>();
// ...
var app = biulder.Build()
// ...

No existing database?

If don't have your database implemented yet, you can create it by mapping using EntityFrameworkCore.

// Program.cs
var scope = app.Services.CreateScope();
var context = scope.ServiceProvider.GetRequiredService<MoviesContext>();
context.Database.EnsureDeleted();
context.Database.EnsureCreated();

For each time you launch the program, EntityFrameworkCore ensures the schema of the database by mapping. We haven't introduce any mapping yet, we'll discuss them later.

WARNING

Don't use it in production code base!