How to add/update child entities when updating a parent entity in EF

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The two entities are one-to-many relationship (built by code first fluent api).

public class Parent
{
    public Parent()
    {
        this.Children = new List<Child>();
    }

    public int Id { get; set; }

    public virtual ICollection<Child> Children { get; set; }
}

public class Child
{
    public int Id { get; set; }

    public int ParentId { get; set; }

    public string Data { get; set; }
}

In my WebApi controller I have actions to create a parent entity(which is working fine) and update a parent entity(which has some problem). The update action looks like:

public void Update(UpdateParentModel model)
{
    //what should be done here?
}

Currently I have two ideas:

  1. Get a tracked parent entity named existing by model.Id, and assign values in model one by one to the entity. This sounds stupid. And in model.Children I don’t know which child is new, which child is modified(or even deleted).

  2. Create a new parent entity via model, and attached it to the DbContext and save it. But how can the DbContext know the state of children (new add/delete/modified)?

What’s the correct way of implement this feature?

14 Answers
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