Introduction
This post is more for self-reference than anything else. Basically, I tend to forget some options for mapping relations with Entity Framework Code First, so I wrote this. If in doing so it helps someone, even better! 
One-to-Many
First, the most basic: one-to-many/many-to-one: an instance of the Master class has lots of Details.
1:publicclass Master
2: {3:public Int32 MasterId { get; set; }
4: 5:publicvirtual ICollection<Detail> Details { get; protected set; }
6: }
1:publicclass Detail
2: {3:public Int32 DetailId { get; set; }
4: 5:publicvirtual Master Master { get; set; }
6: }
One-to-One
The stepchild of database relations. Sometimes it is useful, though: a single Master has an optional Detail, which always refers to an existing Master.
1:publicclass Master
2: {3:public Int32 MasterId { get; set; }
4: 5:publicvirtual Detail Detail { get; set; }
6: }
1:publicclass Detail
2: { 3: [Key]4: [ForeignKey("Master")]
5:public Int32 MasterId { get; set; }
6: 7: [Required]8:publicvirtual Master Master { get; set; }
9: }
Many-to-Many
A single Master can have many Details; each Detail can itself be connected to multiple Masters.
1:publicclass Master
2: {3:public Master()
4: {5:this.Details = new List<Detail>();
6: } 7: 8:public Int32 MasterId { get; set; }
9: 10:publicvirtual ICollection<Detail> Details { get; protected set; }
11: }
1:publicclass Detail
2: {3:public Detail()
4: {5:this.Masters = new List<Master>();
6: } 7: 8:public Int32 DetailId { get; set; }
9: 10:publicvirtual ICollection<Master> Masters { get; protected set; }
11: }
One-to-Many With Composite Key
In this case we have a composite primary key constituted by a foreign key and a scalar column: a Master instance is related with many Details and each Detail is identified by both a single Master and a timestamp.
1:publicclass Master
2: {3:public Master()
4: {5:this.Details = new List<Detail>();
6: } 7: 8:public Int32 MasterId { get; set; }
9: 10:publicvirtual ICollection<Detail> Details { get; protected set; }
11: }
1:publicclass Detail
2: { 3: [Key]4: [ForeignKey("Master")]
5: [Column(Order = 0)]6:public Int32 MasterId { get; set; }
7: 8: [Required]9:publicvirtual Master Master { get; set; }
10: 11: [Key] 12: [Column(Order = 1)]13:public DateTime Timestamp { get; set; }
14: }
Have I forgotten something? Let me know!