entity framework - Unable to cast object of type 'System.Linq.Expressions.FieldExpression' to type 'System.Linq.Expressions.ParameterExpression -

i using entity framework rc1-final in asp.net5.

i have following table.

public class playercomment  {     [key]     public int id { get; set; }      public int? periodid { get; set; }      [foreignkey("periodid")]     public period period { get; set; }      public int? playerid { get; set; }     [foreignkey("playerid")]     public player player { get; set;      public datetime? commentdate { get; set; }      public string comment { get; set; }  } 

playercomment linked player linked subgroup linked group

i have following linq query

public async task<ienumerable<playercomment>>  searchqueryable(int? groupid, int? subgroupid = null, int? playerid = null)     {          var table = (from pc in _db.playercomments                      join p in _db.players on pc.playerid equals p.id                      join sg in _db.subgroups on p.subgroupid equals sg.id                      (sg.groupid == groupid || groupid == null)                          &&                          (p.subgroupid == subgroupid || subgroupid == null)                            &&                          (p.id == playerid || playerid == null)                      select pc);         return table.tolistasync();     } 

this works correctly.

every comment falls in period in output need include period add .include("period")

so code looks this

public async task<ienumerable<playercomment>>  searchqueryable(int? groupid, int? subgroupid = null, int? playerid = null)     {          var table = (from pc in _db.playercomments                      join p in _db.players on pc.playerid equals p.id                      join sg in _db.subgroups on p.subgroupid equals sg.id                      (sg.groupid == groupid || groupid == null)                          &&                          (p.subgroupid == subgroupid || subgroupid == null)                            &&                          (p.id == playerid || playerid == null)                      select pc).include(p => p.period);         return table.tolistasync();     } 

however throws runtime exception , gives me:

"unable cast object of type 'system.linq.expressions.fieldexpression' type 'system.linq.expressions.parameterexpression'."

i read on github there issue orderby giving error i'm not using order by.

is there workaround can use fix this?

i seem have narrowed down answer provided @octavioccl.

changing code this:

        var table = _db.playercomments.include(q => q.period)                       .include(sg => sg.player.subgroup);         iqueryable<playercomment> tablefiltered;         if (playerid != null)         {             tablefiltered = table.where(p => p.player.id == playerid)         }         else         {             if (subgroupid != null)             {                 tablefiltered = table.where(p => p.player.subgroupid == subgroupid)             }             else             {                 if (groupid != null)                 {                     tablefiltered = table.where(p => p.player.subgroup.groupid == groupid)                 }                 else                 {                     tablefiltered = table                 }             }          }         return tablefiltered; 

all combinations work, except when select groupid , keep others null. since subgroup works can deduce issue when use include , use clause 3 levels deep.

you should try calling include method in dbset want load related entity:

 var table = (from pc in _db.playercomments.include(p => p.period)               //... 

and think query simpler if use navigation properties instead explicit joins:

var table =await _db.playercomments.include(p => p.period)                                    .include(p => p.player.subgroup.group)                                    .where(pc=>  ( pc.player.subgroup.group.groupid == groupid || groupid == null)                                               && ( pc.player.subgroup.subgroupid == subgroupid || subgroupid == null)                                              && ( pc.player.id == playerid || playerid == null))                                    .tolistasync(); 

update

try moving conditions check if parameters null outside of query.

bool groupidisnull=groupid == null; bool subgroupidisnull=subgroupid == null; bool playeridisnull= playerid==null;  var table =await _db.playercomments.include(p => p.period)                                    .include(p => p.player.subgroup.group)                                    .where(pc=>  ( groupidisnull || pc.player.subgroup.group.groupid.value == groupid.value)                                               && ( subgroupidisnull || pc.player.subgroup.subgroupid.value == subgroupid.value )                                              && ( playeridisnull || pc.player.id.value == playerid.value))                                    .tolistasync();