Configure One-to-Many Relationships using Fluent API in Entity Framework Core

 

using Microsoft.EntityFrameworkCore;

namespace BlazorApp1;

public class AppDbContext : DbContext
{
    public AppDbContext(DbContextOptions<AppDbContext> options)
        : base(options)
    {
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseNpgsql("Host=localhost;Database=testdb;Username=postgres;Password=12345");
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Student>()
            .HasOne<Grade>(s => s.Grade)
            .WithMany(g => g.Students)
            .HasForeignKey(s => s.CurrentGradeId);
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Grade> Grades { get; set; }
}

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }

    public int CurrentGradeId { get; set; }
    public Grade Grade { get; set; }
}

public class Grade
{
    public int GradeId { get; set; }
    public string GradeName { get; set; }
    public string Section { get; set; }

    public ICollection<Student> Students { get; set; }
}

References
https://www.entityframeworktutorial.net/efcore/configure-one-to-many-relationship-using-fluent-api-in-ef-core.aspx
https://docs.microsoft.com/en-us/ef/core/modeling/relationships?tabs=fluent-api%2Cfluent-api-simple-key%2Csimple-key