Mapping a foreign key with a custom column name

If you don’t want to use fluent syntax, there are three other ways of implementing the reference using data annotations (Personally I prefer data annotations as they seem easier to read and are written just above the property they are affecting):

1.1)
Use ForeignKey (with an associated property) – version 1

[Table("WIDGETENTITIES")]
public class WidgetEntity {

    [Column("WIDGETENTITY_ID")]
    public int Id { get; set; }

    [Column("WIDGETSEQUENCE_ID")]
    public int WidgetSequenceId { get; set; }

    [ForeignKey("WidgetSequenceId")] //Has to be a property name, not table column name
    public WidgetSequence Sequence { get; set; }

    // and other properties that map correctly
}

[Table("WIDGETSEQUENCES")]
public class WidgetSequence { 

    [Column("WIDGETSEQUENCE_ID")]
    public int Id { get; set; }

    [Column("NUMBER")]
    public int Number { get; set; }
}

1.2)
Use ForeignKey (with an associated property) – version 2

[Table("WIDGETENTITIES")]
public class WidgetEntity {

    [Column("WIDGETENTITY_ID")]
    public int Id { get; set; }

    [ForeignKey("Sequence")] //Has to be a property name, not table column name
    [Column("WIDGETSEQUENCE_ID")]
    public int WidgetSequenceId { get; set; }

    public WidgetSequence Sequence { get; set; }

    // and other properties that map correctly
}

[Table("WIDGETSEQUENCES")]
public class WidgetSequence { 

    [Column("WIDGETSEQUENCE_ID")]
    public int Id { get; set; }

    [Column("NUMBER")]
    public int Number { get; set; }
}

2)
You can also use the InversePropertyAttribute.

[Table("WIDGETENTITIES")]
public class WidgetEntity {

    [Column("WIDGETENTITY_ID")]
    public int Id { get; set; }

    [InverseProperty("WidgetEntities")]
    public WidgetSequence Sequence { get; set; }

    // and other properties that map correctly
}

[Table("WIDGETSEQUENCES")]
public class WidgetSequence { 

    [Column("WIDGETSEQUENCE_ID")]
    public int Id { get; set; }

    [Column("NUMBER")]
    public int Number { get; set; }

    public virtual List<WidgetEntity> WidgetEntities { get; set; }
}