CODEWITHSUNDEEP
entity-frameworkef-code-first
DPH
DPH

Reputation: 280

EF6 CodeFirst: Mapping child object

None of the Q&A I've found so far seem to resolve this problem.

I'm in the process of migrating from a custom DAL to EF6, so entity classes and DB already exist. I'm trying to keep DataAnnotations out of the entity classes.

A LiveCourseOpportunity can have a Campaign. And a Campaign can have a LiveCourseOpportunity (at least in the sense that the Campaign class has to have a Navigation Property pointing to its LiveCourseOpportunity). In the database, this is implemented as the LiveCourseOpportunities table having CampaignId as an FK.

Here is the (relevant) code I have so far:

LiveCourseOpportunity entity

public int DatabaseId { get; set; } // PK
public int? CampaignId { get; set; }
public virtual Campaign Campaign { get; set; }

Campaign entity

public int DatabaseId { get; set; } // PK
public virtual ICollection<LiveCourseOpportunity> LiveCourseOpportunities { get; set; }

Model

modelBuilder.Entity<Campaign>()
    .HasKey(T => T.DatabaseId)
    .Property(T => T.DatabaseId)
    .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

modelBuilder.Entity<LiveCourseOpportunity>()
    .HasKey(T => T.DatabaseId)
    .Property(T => T.DatabaseId)
    .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

modelBuilder.Entity<Campaign>()
    .HasMany(c => c.LiveCourseOpportunities)
    .WithOptional(o => o.Campaign)
    .HasForeignKey(o => o.CampaignId);

The relationship directly above comes from an EF reverse-engineering of the database... one-to-many for some reason.

Can anyone advise proper mapping to get this done?

Upvotes: 1

Views: 133

Answers (1)

Gert Arnold
Gert Arnold

Reputation: 109080

For a database, a foreign key is always one to many unless the key field has a unique index.

However, in EF you can map it as an optional one to one association (0..1 - 0..1):

modelBuilder.Entity<Campaign>()
            .HasOptional(e => e.LiveCourseOpportunity)
            .WithOptionalPrincipal(e => e.Campaign)
            .Map(m => m.MapKey("CampaignId"));

The database still doesn't know better than that it's 0..1-n (i.e. there is a nullable foreign key CampaignId), but EF will execute validations to enforce a one-to-one association.

Upvotes: 1

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