Insert new record in pivot table with many to many relationship using Entity Framework Core

Question

I am building an application using ASP.NET Core MVC. I am trying to insert a new record with a many-to-many relationship. I have 3 tables Repairs , Parts and RepairParts .

How can I insert the RepairId and PartId into the RepairParts table? Does EF Core provide something for this? I searched the documentation but it doesn't mention anything about how to do this.

Does Entity Framework do this automatically? (insert to the pivot table) Or do I need to do it manually? An example would help.

Repair class:

public class Repair
{
    [Key]
    public int RepairId { get; set; }

    public int VehicleId { get; set; }
    public string Notes { get; set; }
    public string Mileage { get; set; }
    public DateTime RepairDate { get; set; }
    public string uuid { get; set; }

    [ForeignKey("VehicleId")]
    public Vehicle Vehicle { get; set; }

    public virtual ICollection<RepairParts> RepairParts { get; set; }
}

Part class:

public class Part
{
    public int PartId { get; set; }
    public int Code { get; set; }
    public string PartCode { get; set; }
    public string Type { get; set; }
    public string Name { get; set; }
    public string Descr { get; set; }
    public string Manufacturer { get; set; }
    public string uuid { get; set; }

    public virtual ICollection<RepairParts> RepairParts { get; set; }
}

RepairPart class:

public class RepairParts
{
    public int RepairId { get; set; }
    public Repair Repair { get; set; }

    public int PartId { get; set; }
    public Part Part { get; set; }

    public decimal price { get; set; }
}

DbContext class:

public class ApplicationDbContext : IdentityDbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }

    public DbSet<Customer> Customers { get; set; }
    public DbSet<TaxOffice> TaxOffices { get; set; }
    public DbSet<Vehicle> Vehicles { get; set; }
    public DbSet<Part> Parts { get; set; }
    public DbSet<Repair> Repairs { get; set; }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.Entity<Customer>()
              .HasMany(v => v.Vehicles)
              .WithOne(b => b.Customer);

        builder.Entity<Vehicle>()
             .HasOne(c => c.Customer)
             .WithMany(b => b.Vehicles);

        builder.Entity<Vehicle>()
              .HasMany(v => v.Repairs)
              .WithOne(c => c.Vehicle);

        builder.Entity<RepairParts>()
            .HasKey(t => new { t.RepairId, t.PartId });

        builder.Entity<RepairParts>()
            .HasOne(r => r.Repair)
            .WithMany(t => t.RepairParts)
            .HasForeignKey(f => f.RepairId);

        builder.Entity<RepairParts>()
            .HasOne(r => r.Part)
            .WithMany(p => p.RepairParts)
            .HasForeignKey(f => f.PartId);
    }
}

Answer 1

Here are two options for you:

1. Insert RepairParts by public virtual ICollection<RepairParts> RepairParts { get; set; } public virtual ICollection<RepairParts> RepairParts { get; set; }

    var repaire = new Repair { uuid = "R3" }; var part = new Part { Code = 3 }; var reparePart = new RepairParts { Repair = repaire, Part = part }; repaire.RepairParts = new List<RepairParts>() { reparePart }; _context.Add(repaire); _context.SaveChanges();

2. Insert RepairParts explictly by _context.Add(reparePart1);

    var repaire1 = new Repair { uuid = "RR1" }; var part1 = new Part { Code = 4 }; var reparePart1 = new RepairParts { Repair = repaire1, Part = part1 }; _context.Add(repaire1); _context.Add(part1); _context.Add(reparePart1); _context.SaveChanges();