“error: type mismatch” in Spark with same found and required datatypes

问题

I am using spark-shell for running my code. In my code, I have defined a function and I call that function with its parameters.

The problem is that I get the below error when I call the function.

error: type mismatch;

found   : org.apache.spark.graphx.Graph[VertexProperty(in class $iwC)(in class $iwC)(in class $iwC)(in class $iwC),String]

required: org.apache.spark.graphx.Graph[VertexProperty(in class $iwC)(in class $iwC)(in class $iwC)(in class $iwC),String]

What is the reason behind this error? Has it got anything to do with Graph datatype in Spark?

Code : This is the part of my code which involves the definition and call of the function "countpermissions".

class VertexProperty(val id:Long) extends Serializable
case class User(val userId:Long, val userCode:String, val Name:String, val Surname:String) extends VertexProperty(userId)
case class Entitlement(val entitlementId:Long, val name:String) extends VertexProperty(entitlementId)

def countpermissions(es:String, sg:Graph[VertexProperty,String]):Long = {
    return 0
}

val triplets = graph.triplets
val temp = triplets.map(t => t.attr)
val distinct_edge_string = temp.distinct    
var bcast_graph = sc.broadcast(graph)        
val edge_string_subgraph = distinct_edge_string.map(es => es -> bcast_graph.value.subgraph(epred = t => t.attr == es))
val temp1 = edge_string_subgraph.map(t => t._1 -> countpermissions(t._1, t._2))

The code runs without errors until the last line, where it gets the above mentioned error.

回答1:

Here is the trick. Lets open the REPL and define a class:

scala> case class Foo(i: Int)
defined class Foo

and a simple function which operates on this class:

scala> def fooToInt(foo: Foo) = foo.i
fooToInt: (foo: Foo)Int

redefine the class:

scala> case class Foo(i: Int)
defined class Foo

and create an instance:

scala> val foo = Foo(1)
foo: Foo = Foo(1)

All whats left is to call fooToInt:

scala> fooToInt(foo)
<console>:34: error: type mismatch;
 found   : Foo(in class $iwC)(in class $iwC)(in class $iwC)(in class $iwC)
 required: Foo(in class $iwC)(in class $iwC)(in class $iwC)(in class $iwC)
          fooToInt(foo)

Does it look familiar? Yet another trick to get a better idea what is going on:

scala> case class Foo(i: Int)
defined class Foo

scala> val foo = Foo(1)
foo: Foo = Foo(1)

scala> case class Foo(i: Int)
defined class Foo

scala> def fooToInt(foo: Foo) = foo.i
<console>:31: error: reference to Foo is ambiguous;
it is imported twice in the same scope by
import INSTANCE.Foo
and import INSTANCE.Foo
         def fooToInt(foo: Foo) = foo.i

So long story short this is an expected, although slightly confusing, behavior which arises from ambiguous definitions existing in the same scope.

Unless you want to periodically :reset REPL state you should keep track of entities you create and if types definitions change make sure that no ambiguous definitions persist (overwrite things if needed) before you proceed.

来源：https://stackoverflow.com/questions/37476790/error-type-mismatch-in-spark-with-same-found-and-required-datatypes

标签

scala

apache-spark

spark-graphx