Entity framework The column 'x' was specified multiple times for 'Filter1' - sql

Question

Developing Asp .Net MVC web application. Using Entity framework 6.1.1 and Visual Studio 2013.
Got this Linq:
Db.Distrule_contents.Where(x => x.distrule_id == DistruleId && x.Content.season_id.HasValue && x.Content.season.series_id == SeriesId).Select(x => x.Content).ToList();
and associated with DB tables classes:
[Table("distrule_content")]
public class Distrule_content
{
[Key,Column(Order=0)]
public int distrule_id { get; set; }
[Key, Column(Order = 1)]
[ForeignKey("Content")]
public string IDEC { get; set; }
public int status_id { get; set; }
public virtual Distrule Distrule { get; set; }
public virtual Content Content { get; set; }
public virtual Status Status { get; set; }
}
[Table("distrule")]
public class Distrule: CommonEntity
{
public string distrule_name { get; set; }
public DateTime? begin_date { get; set; }
public DateTime end_date { get; set; }
public int status_id { get; set; }
public int? minutes_to_tx { get; set; }
public string period_type { get; set; }
public bool? autoactivate_content { get; set; }
public virtual ICollection<Distrule_area> DistruleAreas { get; set; }
public virtual ICollection<Distrule_content> DistruleContent { get; set; }
public virtual ICollection<Distrule_georegion> DistruleGeoregion { get; set; }
public virtual Status status { get; set; }
}
[Table("content")]
public class Content
{
[Key]
public string IDEC { get; set; }
public DateTime? date_inserted { get; set; }
public DateTime? min_tx_date { get; set; }
public long? season_id { get; set; }
public int? episode_number { get; set; }
public string content_rus_name { get; set; }
public virtual Season season { get; set; }
}
[Table("status")]
public class Status: CommonEntity
{
public string status_name { get; set; }
}
As a Result receave this SQL Query:
SELECT
[Filter1].[distrule_id1] AS [distrule_id],
[Filter1].[IDEC1] AS [IDEC],
[Filter1].[date_inserted1] AS [date_inserted],
[Filter1].[min_tx_date1] AS [min_tx_date],
[Filter1].[season_id1] AS [season_id],
[Filter1].[episode_number1] AS [episode_number],
[Filter1].[content_rus_name1] AS [content_rus_name],
[Filter1].[season_id2] AS [season_id1]
FROM ( SELECT [Extent1].[distrule_id] AS [distrule_id1], [Extent1].[Distrule_Id] AS [distrule_id1], [Extent2].[IDEC] AS [IDEC1], [Extent2].[date_inserted] AS [date_inserted1], [Extent2].[min_tx_date] AS [min_tx_date1], [Extent2].[season_id] AS [season_id1], [Extent2].[episode_number] AS [episode_number1], [Extent2].[content_rus_name] AS [content_rus_name1], [Extent2].[season_Id] AS [season_id1], [Extent3].[series_id] AS [series_id1], [Extent3].[Series_Id] AS [series_id1], [Extent4].[season_id] AS [season_id2], [Extent4].[season_Id] AS [season_id2]
FROM [dbo].[distrule_content] AS [Extent1]
INNER JOIN [dbo].[content] AS [Extent2] ON [Extent1].[IDEC] = [Extent2].[IDEC]
LEFT OUTER JOIN [dbo].[Season] AS [Extent3] ON [Extent2].[season_Id] = [Extent3].[Id]
LEFT OUTER JOIN [dbo].[content] AS [Extent4] ON [Extent1].[IDEC] = [Extent4].[IDEC]
WHERE [Extent2].[season_id] IS NOT NULL
) AS [Filter1]
WHERE ([Filter1].[distrule_id1] = #p__linq__0) AND ([Filter1].[series_id1] = #p__linq__1)
And following error: The column 'distrule_id1' was specified multiple times for 'Filter1'.
What i am doing wrong?
update 2014-09-10
Solved after deep study EF navigation rules. Thx to chconger. Problem was in letting EF self realize where FK should be placed. So after adding everywhere ForeignKey attribute is worked fine.
Here how it looks now:
[Table("distrule_content")]
public class Distrule_content
{
[Key,Column(Order=0)]
public int distrule_id { get; set; }
[Key, Column(Order = 1)]
[ForeignKey("Content")]
public string IDEC { get; set; }
public int status_id { get; set; }
[ForeignKey("distrule_id")]
public virtual Distrule Distrule { get; set; }
[ForeignKey("IDEC")]
public virtual Content Content { get; set; }
[ForeignKey("status_id")]
public virtual Status Status { get; set; }
}

Answer 1

Couple of issues from what I can see.
1. You have a foreign key set above a mismatched string IDEC, instead
[Key, Column(Order = 1)]
[ForeignKey("Content")]
public virtual Content Content { get; set; }
2. You are missing a constructor with HashSets for your class Distrule
public Distrule()
{
DistruleAreas = new HashSet<DistruleArea>();
DistruleContents = new HashSet<DistruleContent>();
DistruleGeoregions = new HashSet<DistruleGeregion>();
}