entity framework - WithRequiredPrincipal, why still have to define Required or ForeignKey to be able to compile? -

public class admin : entitytypeconfiguration<admin> {     //[foreignkey("blog")] -- if enable this, compiles     public int adminid { get; set; }     public string adminname { get; set; }     public string adminpicture { get; set; }      //[required] -- or if enable this, compiles     public virtual blog blog { get; set; } }  public class blog : entitytypeconfiguration<blog> {     public int blogid { get; set; }     public string blogname { get; set; }     public string blogurl { get; set; }      public virtual admin admin { get; set; }      public blog()     {         hasrequired(a => a.admin).withrequiredprincipal(b=>b.blog);     } } 

as long defining hasrequired , withrequiredprincipal keys, why vs still creates below error.

unable determine principal end of association between types 'dummy.models.blog' , 'dummy.models.admin'. principal end of association must explicitly configured using either relationship fluent api or data annotations.

second thing is, enable [required] or [foreingkey] attr., in edmx designer, see 1 - 0..1 must see 1 - 1 (both end required)

1-1 relationship not possible @ database level, because can't insert 2 rows @ same time. 1-1 possible @ class validation level.

to make 1-1 relationship, primary key of dependant entity must foreign key of principal entity; that's way make 1-1 relationship. so, have make following changes (considering using ef code first):

public class admin {     public int adminid { get; set; }     public string adminname { get; set; }     public string adminpicture { get; set; }      public virtual blog blog { get; set; } } 

blog should not have own blogid, because blog belongs admin, , admin can have 1 blog (1-1 relationship). if create blogid, adminid fk, making 1-n relationship. furthermore, not mix entity class mapping class, should different things. see example below:

public class blog {     public int adminid { get; set; } //pk , fk     public string blogname { get; set; }     public string blogurl { get; set; }      public virtual admin admin { get; set; }          } 

creating relationship mapping class:

public class blogmapping : entitytypeconfiguration<blog> {     public blogmapping()     {         haskey(i => i.adminid);          hasrequired(a => a.admin)             .withrequireddependent(i => i.blog);     } } 

register mapping inside dbcontext class:

public class mydbcontext : dbcontext {     public dbset<admin> admins { get; set; }     public dbset<blog> blogs { get; set; }       protected override void onmodelcreating(dbmodelbuilder modelbuilder)     {         modelbuilder.configurations.add(new blogmapping());     } } 

this generate following migration:

createtable(     "dbo.admins",     c => new         {             adminid = c.int(nullable: false, identity: true),             adminname = c.string(),             adminpicture = c.string(),         })     .primarykey(t => t.adminid);  createtable(     "dbo.blogs",     c => new         {             adminid = c.int(nullable: false),             blogname = c.string(),             blogurl = c.string(),         })     .primarykey(t => t.adminid)     .foreignkey("dbo.admins", t => t.adminid)     .index(t => t.adminid); 

hope helps!