c# - EF optional one to many multiplicity error -

i have simple schema, simplified further question

table: airport iata char(3) primary key name varchar(20)  table: airport_terminal iata char(3) (comp key1) terminalname (comp key2)  pocos public sealed class airport {     [key]     public string iata { get; set; }             public string name { get; set; }      public icollection<airportterminal> terminals { get; set; } }      public class airportterminal {     [key, column(order = 0)]     public string iata { get; set; }      [key, column(order = 1)]     public string terminal { get; set; }      public airport airport { get; set; }  } 

airportterminal configuration

modelbuilder.entity<airportterminal>()     .hasoptional<airport>(s => s.airport)     .withmany(s => s.terminals)     .hasforeignkey(s => s.iata); 

some airports (in application) have multiple terminals , not. want react terminals property when there terminals defined given airport. if enter single record every airport, configuration works. when attempt lookup airport, get:

 "one or more validation errors detected during model generation: multiplicity conflicts referential constraint in role 'airportterminal_airport_target' in relationship 'airportterminal_airport'. because of properties in dependent role non-nullable, multiplicity of principal role must '1'." 

research shows error occurs when non-nullable property exists on optional member, cannot set null. airportterminal contains 2 strings, nullable.

any ideas?

consider using key tables. best instead of multiple key. place index constraint ensure uniqueness in properties iata , terminal.

pocos:

public sealed class airport {     [key]     public guid id { get; set; }      public string iata { get; set; }             public string name { get; set; }      public icollection<airportterminal> terminals { get; set; } }  public class airportterminal {     [key]     public guid id { get; set; }      public string iata { get; set; }      public string terminal { get; set; }      public airport airport { get; set; }      public guid? airportid { get; set; } } 

configuration:

modelbuilder.entity<airportterminal>()     .hasoptional<airport>(s => s.airport)     .withmany(s => s.terminals)     .hasforeignkey(s => s.airportid);