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https://issues.apache.org/jira/browse/FLINK-6024?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15907427#comment-15907427
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Kostas Kloudas edited comment on FLINK-6024 at 3/13/17 1:12 PM:
----------------------------------------------------------------
I totally agree that the Error message should be more explanatory.
With the fix for the Streaming API, we just do not accept any Arrays as keys
and for POJOs we check if the class overrides the {{hashCode}} method.
Essentially the check is
{code}
(type instanceof PojoTypeInfo) {
?
!type.getTypeClass().getMethod("hashCode").getDeclaringClass().equals(Object.class)
: !(type instanceof PrimitiveArrayTypeInfo || type instanceof
BasicArrayTypeInfo || type instanceof ObjectArrayTypeInfo)
{code}
Still you can violate the contract and provide an invalid key by using a
{{KeySelector}} that returns {{Object}} as a key. The reason is that we get the
type of the key from the {{TypeInformation}}, which now will think that your
key is a simple {{Object}}. The reason for allowing it is because many people
leave their {{KeySelector}} implementation return {{Object}}, which is the
default.
was (Author: kkl0u):
I totally agree that the Error message should be more explanatory.
With the fix for the Streaming API, we just do not accept any Arrays as keys
and for POJOs we check if the class overrides the {{hashCode}} method.
Essentially the check is
{{
(type instanceof PojoTypeInfo) {
?
!type.getTypeClass().getMethod("hashCode").getDeclaringClass().equals(Object.class)
: !(type instanceof PrimitiveArrayTypeInfo || type instanceof
BasicArrayTypeInfo || type instanceof ObjectArrayTypeInfo)
}}
Still you can violate the contract and provide an invalid key by using a
{{KeySelector}} that returns {{Object}} as a key. The reason is that we get the
type of the key from the {{TypeInformation}}, which now will think that your
key is a simple {{Object}}. The reason for allowing it is because many people
leave their {{KeySelector}} implementation return {{Object}}, which is the
default.
> Need more fine-grained info for "InvalidProgramException: This type (...)
> cannot be used as key"
> ------------------------------------------------------------------------------------------------
>
> Key: FLINK-6024
> URL: https://issues.apache.org/jira/browse/FLINK-6024
> Project: Flink
> Issue Type: Improvement
> Components: Core
> Affects Versions: 1.2.0
> Reporter: Luke Hutchison
>
> I got this very confusing exception:
> {noformat}
> InvalidProgramException: This type (MyType) cannot be used as key
> {noformat}
> I dug through the code, and could not find what was causing this. The help
> text for type.isKeyType(), in Keys.java:329, right before the exception is
> thrown, says: "Checks whether this type can be used as a key. As a bare
> minimum, types have to be hashable and comparable to be keys." However, this
> didn't solve the problem.
> I discovered that in my case, the error was occurring because I added a new
> constructor to the type, and I didn't have a default constructor. This is
> probably quite a common thing to happen for POJOs, so the error message
> should give some detail saying that this is the problem.
> Other things that can cause this to fail, including that the class is not
> public, or the constructor is not public, or the key field is not public, or
> that the key field is not a serializable type, or the key is not Comparable,
> or the key is not hashable, should be given in the error message instead,
> depending on the actual cause of the problem.
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