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This question may be simple, but the logic is important and I'm confused about it. In Asp.Net Core 2.1 with Entity Framework Core Code First, I want to learn how to model, so i have simplified the problem. One same navigation property (Photo) in two different entity (Center and Article). Center can has many photos and article can has one photo. A photo can has one post or one center, so can has one MyEntityBase. Example:

public class Photo
{
    public int Id { get; set; }
    public string Url { get; set; }

    //The question/relation problem is here???
    //public int CenterId { get; set; }
    //public virtual Center Center { get; set; }

    //public int ArticleId { get; set; }
    //public virtual Article Article{ get; set; }

    //public int MyEntityBaseId { get; set; }
    //public virtual MyEntityBase ArticleOrPost{ get; set; }
}

public class Article: MyEntityBase
{
    [Key]
    public int Id { get; set; }

    public string Title { get; set; } 

    //Common Photo property
    //One article has one photo
    public virtual Photo ArticlePhoto { get; set; }

}
public class Center: MyEntityBase
{
    [Key]
    public int Id { get; set; }

    public string Name{ get; set; } 

    //Common Photo property
    //One center has many photo
    public virtual List<Photo> CenterPhotos { get; set; }

}
Aykarnz
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1 Answers1

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At first glance, if you are using Entity Framework Core... don't use virtual

so your Article object should look like this

public class Article: MyEntityBase
{
    [Key]
    public int Id { get; set; }

    public string Title { get; set; } 

    public int ArticlePhotoId { get; set; }

    //Common Photo property
    //One article has one photo
    public Photo ArticlePhoto { get; set; }

}

your photo object looks correct with the CenterId the line below it remove the virtual

in your Center object, use ICollection instead of List

the rest should just map automatically without a configuration file.

Edit: On regards to virtual if you are using lazy loading then it seems to be supported, but configuration is needed to set that up. I'd keep things as simple as possible first and verify that it works then add lazy loading.

reference: navigation property should be virtual - not required in ef core?

Karl Merecido
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  • I have edited like you said and it works. But actually, i cant understand clearly this subject. In Database structure; photo table has centerid fiels but no postid. Is it normal? Why? center table has no photoid field, so i think it looks normal, because its icollection. however post table has no photoid field. it looks strange or normal?. Thanks. – Aykarnz Mar 06 '19 at 18:20
  • @Aykarnz what does your Post object look like? I'm making an assumption but does your Post have multiple photos so its an ICollection... there might be another table that has been created by EF that takes foreign keys from both Posts and Photos... like a PostPhoto or PhotoPost table. In this structure you could have multiple photos and posts associated with each other. – Karl Merecido Mar 07 '19 at 18:20