c# - joining two tables in entity framework -

i'm trying join 2 tables in entity framework , value 1 of them query on third table query i'm using

  var fav = favs in db.favorites                        join pins in db.pins                       on new { favs.user_id, favs.pin_id } equals new { userid, pins.pin_id } res                       r in res                       select new { favs.pin_id, r.type_id }; 

but gives me syntax error in the type of 1 of expressions in join clause incorrect. type inference failed in call 'groupjoin' have searched error , find people make sure properties in equals clause same type, , yes of type non nullable int

when doing linq join, types on either side of equals must same, in query have user_id vs. userid.

the fix simply:

 var fav = favs in db.favorites            join pins in db.pins                on new { favs.user_id, favs.pin_id }                 equals                 // use explicit naming first property gets name user_id not userid                new { user_id = userid, pins.pin_id }                 res            r in res            select new { favs.pin_id, r.type_id }; 

it's bit easier see why necessary if work fluent syntax groupjoin (what you're doing here due "into" clause; regular join similar).

the signature is:

public static iqueryable<tresult> groupjoin<touter, tinner, tkey, tresult>(     iqueryable<touter> outer,     ienumerable<tinner> inner,     expression<func<touter, tkey>> outerkeyselector,     expression<func<tinner, tkey>> innerkeyselector,     expression<func<touter, ienumerable<tinner>, tresult>> resultselector ) 

note outerkeyselector , innerkeyselector must return same type tkey (the join done matching these keys).

to write original join in fluent style, you'd have:

var fav = db.favorites.groupjoin(     inner: inner,     // return types of selectors don't match, compiler can't     // infer type tkey!     outerkeyselector: favs => new { favs.user_id, favs.pin_id },     innerkeyselector: pins => new { userid,       pins.pin_id },     resultselector: (favs, res) => res.select(r => new { favs.pin_id, r.type_id }) ) .selectmany(res => res);