How to add a parent record with its children records in EF Core

Saving child objects along with their parent definitely works. The key is you need to model your entities in such a way that EF knows about all the relationships. Here is a really simple application doing it that you can take a look at. Simple app on github

I have a parent that looks like

using System.Collections.Generic;

namespace EFParentChild
{
    public class Parent
    {
        public int ParentId { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public List<Child> Children { get; set; } = new List<Child>();
    }
}

here's the child

namespace EFParentChild
{
    public class Child
    {
        public int Id { get; set; }
        public int ParentId { get; set; }
        public Parent Parent { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}

Here is the context:

using Microsoft.EntityFrameworkCore;

namespace EFParentChild
{
  class DbParentChild : DbContext
  {
    public DbSet<Parent> Parents { get; set; }
    public DbSet<Child> Children { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=ParentChildDb;Trusted_Connection=True;");
    }

  }
}

Here is the program that saves the data

static void Main(string[] args)
    {
        using (var dbContext = new DbParentChild())
        {
            var parent = new Parent
            {
                FirstName = "Joe",
                LastName = "Smith"
            };

            parent.Children.Add(
                new Child
                {
                    FirstName = "LittleJoe",
                    LastName = "Smith"
                });
            parent.Children.Add(
                new Child
                {
                    FirstName = "Anne",
                    LastName = "Smith"
                });

            dbContext.Add(parent);
            dbContext.SaveChanges();
        }
    }

The key here is that I'm using conventions to tell EF that there is a parent-child relations. Notice how the id names used between the two entities match up. The child has a ParentId that matches ParentId in its parent. Also noticed the foreign key constraint in the child.

I created the tables using the entity framework tooling. You can take that approach yourself or create them by hand if you want. The parent DDL is :

CREATE TABLE [dbo].[Parents] (
[ParentId]  INT            IDENTITY (1, 1) NOT NULL,
[FirstName] NVARCHAR (MAX) NULL,
[LastName]  NVARCHAR (MAX) NULL,
CONSTRAINT [PK_Parents] PRIMARY KEY CLUSTERED ([ParentId] ASC)
);

The child DDL is:

CREATE TABLE [dbo].[Children] (
[Id]        INT            IDENTITY (1, 1) NOT NULL,
[FirstName] NVARCHAR (MAX) NULL,
[LastName]  NVARCHAR (MAX) NULL,
[ParentId]  INT            NOT NULL,
CONSTRAINT [PK_Children] PRIMARY KEY CLUSTERED ([Id] ASC),
CONSTRAINT [FK_Children_Parents_ParentId] FOREIGN KEY ([ParentId]) 
REFERENCES [dbo].[Parents] ([ParentId]) ON DELETE CASCADE
);


GO
CREATE NONCLUSTERED INDEX [IX_Children_ParentId]
  ON [dbo].[Children]([ParentId] ASC);

I'm assuming your have auto generated id for parent entity, in that case you need to add parent entity to DbSet and save changes in order to EF Core sets the generated value for property.

Try this code and you'll save the information:

// Create instance for parent class
var p = new Parent { Name = "some name", FY = SelectedYear, ... };

// Add entity instance to db context
_context.Parent.Add(p);

// Save changes, this action sets the generated id value to entity's property
_context.SaveChanges();

// Create instances for child entities
var c1 = new Child { ItemName = "Abc", ParentID = p.ParentID };
var c2 = new Child { ItemName = "Rst", ParentID = p.ParentID };

// Add child to db context
_context.Child.Add(c1);
_context.Child.Add(c2);

// Save changes
_context.SaveChanges();

It seems like saving fails because each child instance doesn't have value for ParentID property and that column doesn't allow null values.

Let me know if this is useful