EF 6 Code First relationships using Fluent API. How to set relation between first and third tables or get grouped collection - entity-framework

Question

I have three related entities, here is a structure and relations declared using Fluent API
An event, participating many persons (actually a group of persons) so there is a possibility to collect them all by GroupID. So how to do this?
public class Event
{
public int EventID { get; set; }
public string DocID { get; set; }
public string GroupID { get; set; }
public virtual Person Person { get; set; }
public virtual Group Group { get; set; }
public virtual ICollection<Person> GroupPerson {get; set}
}
Person entity, here I have all information about person, such as name, surname, birthdate...
public class Person
{
public string PersonID { get; set; }
public string PersonName { get; set; }
public string PersonSurName { get; set; }
public string PersonCode { get; set; }
}
Group entity, here is an information about the group
public class Group
{
public string GroupID { get; set; }
public string GroupName { get; set; }
public virtual ICollection<Event> EventGroup { get; set; }
}
Now I describe relations using Fluent API. Primary keys first of all:
modelBuilder.Entity<Event>().HasKey(e => e.EventID);
modelBuilder.Entity<Person>().HasKey(e => e.PersonID);
modelBuilder.Entity<Group>().HasKey(e => e.GroupID);
Here I will have person related to event
modelBuilder.Entity<Event>()
.HasRequired(s => s.Person)
.WithMany()
.HasForeignKey(fk=> fk.PersonID);
Here I will have PersonGroup
modelBuilder.Entity<Group>()
.HasKey(e => e.GroupID)
.HasMany(e => e.EventGroup)
.WithOptional()
.HasForeignKey(f => f.GroupID);
And my question is how to set a relation to get that list of persons in group?
PersonGroup is an Event type and I need list of persons type: Person => ICollection<Person> GroupPerson in Event class.

Answer 1

Given that your relationships are like this:
One event has (is related to) exactly one group (required)
One group has (is related to) zero to many events
One group has (is related to) zero to many people
One person has (is related to) zero to many groups
That is, your relationship Events-Groups is one-to-many, and your relationship Groups-People is many-to-many (I'm assuming that the same person can be in more than one group). There is no direct relationship between Events and People, but a transitive relationship Event -> Group -> People.
Then it can be modelled like this:
public class Event
{
public int EventID { get; set; }
public string DocID { get; set; }
public string GroupID { get; set; }
public virtual Group Group { get; set; }
public virtual ICollection<Person> People { get { return Group.People; } }
}
public class Person
{
public string PersonID { get; set; }
public string PersonName { get; set; }
public string PersonSurName { get; set; }
public string PersonCode { get; set; }
}
public class Group
{
public string GroupID { get; set; }
public string GroupName { get; set; }
public virtual ICollection<Event> Events { get; set; }
public virtual ICollection<Person> People { get; set; }
}
With these DbSets in the DbContext:
public DbSet<Person> People { get; set; }
public DbSet<Group> Groups { get; set; }
public DbSet<Event> Events { get; set; }
And this EF configuration:
modelBuilder.Entity<Event>()
.HasKey(e => e.EventID)
.Ignore(e => e.People)
.HasRequired(e => e.Group)
.WithMany(g => g.Events);
modelBuilder.Entity<Group>()
.HasKey(g => g.GroupID)
.HasMany(g => g.People)
.WithMany();
modelBuilder.Entity<Person>()
.HasKey(p => p.PersonID);
Note that there is an explicit Ignore() for Event.People. This is because the relationship between Event and Person is transitive, you don't need extra columns in your database for it. If you don't see why, try commenting out the Ignore() line and regenerating the migration, and see that an extra column for the Event ID is generated in the People table (this column doesn't make much sense).
As a consequence the People property in Events is not populated by EF, you have to do it yourself:
public virtual ICollection<Person> People { get { return Group.People; } }
To add people to an Event you should use the Group navigation property, something like this:
public class Event
{
...
public void AddPerson(Person p)
{
this.Group.People.Add(p);
}
}
With this code the migration is generated like this, with four tables: Events, Groups, People and and extra table PeopleGroups for the many-to-many relationship between Person and Group.
public override void Up()
{
CreateTable(
"dbo.Events",
c => new
{
EventID = c.Int(nullable: false, identity: true),
DocID = c.String(),
GroupID = c.String(nullable: false, maxLength: 128),
})
.PrimaryKey(t => t.EventID)
.ForeignKey("dbo.Groups", t => t.GroupID, cascadeDelete: true)
.Index(t => t.GroupID);
CreateTable(
"dbo.Groups",
c => new
{
GroupID = c.String(nullable: false, maxLength: 128),
GroupName = c.String(),
})
.PrimaryKey(t => t.GroupID);
CreateTable(
"dbo.People",
c => new
{
PersonID = c.String(nullable: false, maxLength: 128),
PersonName = c.String(),
PersonSurName = c.String(),
PersonCode = c.String(),
})
.PrimaryKey(t => t.PersonID);
CreateTable(
"dbo.GroupPersons",
c => new
{
Group_GroupID = c.String(nullable: false, maxLength: 128),
Person_PersonID = c.String(nullable: false, maxLength: 128),
})
.PrimaryKey(t => new { t.Group_GroupID, t.Person_PersonID })
.ForeignKey("dbo.Groups", t => t.Group_GroupID, cascadeDelete: true)
.ForeignKey("dbo.People", t => t.Person_PersonID, cascadeDelete: true)
.Index(t => t.Group_GroupID)
.Index(t => t.Person_PersonID);
}
If you don't like the names of the columns in the relationship table GroupPersons you can add a .Map() configuration (but you don't really need to do this, as this table isn't directly used, there is no model entity for it, and it doesn't even have a DbSet property in the DbContext).