asp.net mvc - SaveChanges not setting value, selecting existing value instead -

when trying commit modified entry database, entity framework selecting values 2 properties opposed setting them.

the code commit entity database follows:

[httppost] [validateantiforgerytoken] public actionresult edit(till till) {     if (modelstate.isvalid)     {         string username = user.identity.name.substring(user.identity.name.lastindexof('\\') + 1);          till.modifieddate = datetime.now;         till.modifiedbyuid_fk = db.users.where(m => m.name.tolower() == username.tolower()).first().useruid_pk;          db.entry(till).state = entitystate.modified;         db.savechanges();          return redirecttoaction("index/" + (int)session["siteid"]);     }     viewbag.siteuid_fk = new selectlist(db.sites, "siteuid_pk", "name", till.siteuid_fk);     viewbag.modifiedbyuid_fk = new selectlist(db.users, "useruid_pk", "ehlogin", till.modifiedbyuid_fk);     viewbag.createdbyuid_fk = new selectlist(db.users, "useruid_pk", "ehlogin", till.createdbyuid_fk);     return view(till); } 

when viewed in profiler, looks this:

exec sp_executesql n'update [dbo].[till] set [networkid] = @0, [mid] = @1, [siteuid_fk] = @2, [location] = null, [mastertillno] = @3,     [ismaster] = @4, [isbackoffice] = @5, [iscurrent] = @6, [modifiedbyuid_fk] = @7,      [createdbyuid_fk] = @8, [processfiles] = @9 ([tilluid_pk] = @10) select [modifieddate], [createddate] [dbo].[till] @@rowcount > 0 , [tilluid_pk] = @10',n'@0 varchar(50),@1 int,@2 int,@3 int,@4 bit,@5 bit,@6      bit,@7 int,@8 int,@9 bit,@10 int',     @0='',@1='',@2=4,@3=42,@4=1,@5=0,@6=1,@7=4,@8=1,@9=1,@10=699 

i'm guessing there's property of field in database ef uses determine functionality can't figure out is. if has information that'd fantastic :)

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edit 1

using ibrahim's answer below, results in relatively similar sql:

exec sp_executesql n'declare @p int update [dbo].[till] set @p = 0 ([tilluid_pk] = @0) select [modifieddate], [createddate] [dbo].[till] @@rowcount > 0 , [tilluid_pk] = @0',n'@0 int',@0=687 

this typically happens when properties have data annotation

[databasegenerated(databasegeneratedoption.computed)] 

or fluent mapping

.hasdatabasegeneratedoption(databasegeneratedoption.computed) 

or storegeneratedpattern computed in edmx file.

i'd guess there trigger or default value on modifieddate , createddate on columns in database. maybe it's useless set them in application code.