如何首先使用代码属性设置一对多关系？

Question

Entity framework throws an exception when I try and save an object. Probably it's because of a many to one relationship and it doesn't know how to insert.

Models:

public class Photo
{
    public Guid Id {get;set;}
    public List<Tag> Tags {get;set;}
}

public class Tag
{
    public Guid Id {get;set;}
    public string TagText {get;set;}
}

This works fine if i dont try and link two or more Photos to the same tag.

Example:

Photo photo1 = new Photo();
Photo photo2 = new Photo();
Tag tag = new Tag() { TagText = "#EntityFramework"};
photo1.Tags.Add(tag);
photo2.Tags.Add(tag);
_content.SaveChanges(); //Exception 

Anyone know how to set this up correctly with code first?

---

Update:

Exception: Additional information: Multiplicity constraint violated. The role 'X' of the relationship 'X' has multiplicity 1 or 0..1.

---

Update:

Script generated by add-migration

 CreateTable(
            "dbo.Tags",
            c => new
                {
                    Id = c.Guid(nullable: false, identity: true),
                    TagText = c.String(),
                    Photo_Id = c.Guid(),
                })
            .PrimaryKey(t => t.Id)
            .ForeignKey("dbo.Photos", t => t.Photo_Id)
            .Index(t => t.Photo_Id);

Answer 1

Also define a collection property in Tag for many to many:

public class Tag
{
    ...
    public ICollection<Photo> Photos { get; set; }
}