How to Prevent Entity Framework from Saving Child Entities When Saving a Parent Entity?

How to Prevent Entity Framework from Saving Child Objects

When using Entity Framework, saving an entity may inadvertently attempt to save associated child entities. To rectify this and solely persist the specified entity, consider the following approaches:

Using EntityState

You can set the EntityState of the child object to Unchanged, informing Entity Framework to leave it untouched:

using (var context = new DatabaseContext())
{
    context.Set<School>().Add(newItem);
    context.Entry(newItem.City).State = EntityState.Unchanged;
    context.SaveChanges();
}

Utilizing Foreign Keys

A more flexible approach involves leveraging foreign keys. When defining entities, specify the foreign key property on the child entity and the corresponding primary key property on the parent entity:

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

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

    [ForeignKey("City_Id")]
    public City City { get; set; }

    [Required]
    public int City_Id { get; set; }
}

During entity insertion, explicitly set the child object's foreign key property and set the parent object's navigation property to null:

    public School Insert(School newItem, int cityId)
    {
        if (cityId <= 0)
        {
            throw new Exception("City ID not provided");
        }

        newItem.City = null;
        newItem.City_Id = cityId;

        using (var context = new DatabaseContext())
        {
            context.Set<School>().Add(newItem);
            context.SaveChanges();
        }
    }

By following these techniques, you can control the persistence of child objects, ensuring that only desired entities are saved and preventing potential integrity issues.

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