c# - how to use entity framework code first the mapping about one to one -

all,i have question don't know how use entity framework code frist. have 2 table tba , tbb

    create table tba (     [id] int not null identity(1,1) constraint [pk_tba] primary key,     [name] varchar(50) not null )      create table tbb (     [id] int not null identity(1,1) constraint [pk_tbb] primary key,     [name] varchar(50) not null,     [tbaid] int not null ) 

in database don't have use forgin key.

this code,i don't know how mapping looks 1 one relationship

class program {     static void main(string[] args)     {         string connectionstring = "data source=localhost;database=demo;integrated security=true";         mydbcontext db = new mydbcontext(connectionstring);         db.tba.asparallel().forall(x => {             console.writeline("{0}----{1}", x.tbaid, x.tbaname);         });          //here throw error         db.tbb.asparallel().forall(x => {             console.writeline("{0}--{1}--{2}--{3}", x.tbbid, x.tbbname, x.mytba.tbaid, x.mytba.tbaname);         });         console.readline();     } }  public class mydbcontext : dbcontext {     public dbset<tba> tba { get; set; }     public dbset<tbb> tbb { get; set; }      public mydbcontext(string connectionstring)         : base(connectionstring)     {      }      protected override void onmodelcreating(dbmodelbuilder modelbuilder)     {         modelbuilder.configurations.add(new tbamapping());         modelbuilder.configurations.add(new tbbmapping());         base.onmodelcreating(modelbuilder);     } }  public class tba {     public int tbaid { get; set; }      public string tbaname { get; set; } }  public class tbb {     public int tbbid { get; set; }     public string tbbname { get; set; }     public tba mytba { get; set; } }  public class tbamapping : entitytypeconfiguration<tba> {     public tbamapping()     {         totable("tba");         haskey(x => x.tbaid);         property(x => x.tbaid).isrequired().hascolumnname("id");         property(x => x.tbaname).isrequired().hascolumnname("name");     } }  public class tbbmapping : entitytypeconfiguration<tbb> {     public tbbmapping()     {         totable("tbb");         haskey(x => x.tbbid);         property(x => x.tbbid).isrequired().hascolumnname("id");         property(x => x.tbbname).isrequired().hascolumnname("name");         // here, how setting mapping  tba.id here     } } 

first of must declare tba mytba virtual,

public virtual tba mytba{get;set;}
 (*)public int tbaid{get;set;}

then can configure relations on typeconfiguration.
need foreignkeytoa in b class.(*)

hasrequired(x=>x.mytba).withoptional().hasforeignkey(x=>x.foreignkeytoa);

if put

.withoptional(empty).

thas tell entity class has not foreign key b.