entity framework - Type arguments error in LINQ extension method -

i wrote linq extension join 2 tables

public static ienumerable<objectdetail<tleft, string>> todetail<tleft, tright, tkey>(this ienumerable<tleft> left, ienumerable<tright> right, func<tleft, tkey> leftproperty, func<tright, tkey> rightproperty, func<tright, tkey> keyproperty, func<tright, tkey> valueproperty, string keyselector)         {             return (from l in left                     join r in right on leftproperty(l) equals rightproperty(r) 1                     select new                     {                         l,                         1                     }).asenumerable().select(q => new objectdetail<tleft, string>                     {                         item = q.l,                         meta = q.one.where(m => keyselector.contains(keyproperty(m).tostring())).todictionary(m => keyproperty(m).tostring(), m => valueproperty(m).tostring())                     });         } 

the compiler understand extension when try write

var result = left.todetail(right, l => l.id, r => r.id, r => r.key, r => r.value, "key"); 

i got following error:

the type arguments method .todetail(system.collections.generic.ienumerable, system.collections.generic.ienumerable, system.func, system.func, system.func, system.func, string)' cannot inferred usage. try specifying type arguments explicitly

then tried remove keyproperty , valueproperty parameters extension, run without error. don't know why, maybe compiler confused , cannot determine parameter same type?

any helps appreciated!

in function declaration, use same function type rightproperty, keyproperty , valueproperty arguments, both of these functions should have type func<tright, tkey>.

this means when call function, type of r.id, r.key , r.value must same (so c# compiler can infer tkey type parameter these two). guess in example, @ least 1 of these 3 different (probably id).

(aside, since you're converting result of valueselector , keyselector string using tostring method, there no reason why need use generic types - function returning object should trick).