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https://issues.apache.org/jira/browse/SQOOP-1549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14157525#comment-14157525
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Jarek Jarcec Cecho commented on SQOOP-1549:
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I would do one step back and look at it from the bigger picture perspective.
Whereas it might seem that having just one Configuration class will simplify
the {{SqoopConnector}} class, I'm not that sure that it will then apply for
entire connector development. The configuration classes are subsequently used
in a bunch of APIs where the connector developer can use them to retrieve user
supplied value - in extractor, loader, initializer, ... .
The beauty of separate classes is that when I'm calling "From" Initializer I'm
given a "From" Configuration class and I do have all the power of Java type
system checking that I've got the class that I was suppose to with values that
I care about. If we say that there is only one class for the entire
configuration, then this beauty will disappear and connector developer will be
held responsible to ensure that he is accessing only values that are valid for
given context. That seems much more concerning to me then a need to create
couple of extra classes. If the concern and motivation is that you have to
create three extra classes, then another solution is to provide default empty
class and return it by default directly in {{SqoopConnector}} class. This way
connector developer have to specify it's own class only if he cares about that.
> Simplifying the Configuration class concept in Connector api
> ------------------------------------------------------------
>
> Key: SQOOP-1549
> URL: https://issues.apache.org/jira/browse/SQOOP-1549
> Project: Sqoop
> Issue Type: Sub-task
> Reporter: Veena Basavaraj
> Assignee: Veena Basavaraj
>
> Here is what happens today ( SQOOP-1367 ) when someone needs to write a
> connector.
> First they start looking at the connector api and sees that they need to
> implement configuration classes. Well after some thinking they realize, they
> need 3 classes. Why they wonder? But they continue on and implement 3
> classes. In some cases there is really nothing for Link Configuration, but
> they still have to create this dummy class for a Configuration Class and then
> another dummy one for config class, which if it were me would find it absurd.
> Then after creating 3 configuration classes, they need to then create atleast
> 3 config classes. Note the use of word atleast. The api is not at all
> obvious in telling them that they infact can create more than 3 config
> classes. It seems like a hidden feature unless until someone sees some sample
> code where there is more than one config class per configuration class. !!
> The naming "getJobConfigurationClass" tells them nothing. You may say javadoc
> could explain it, But I wonder why we need to even support 3 configuration
> classes and more than 3 config classes.
> {code}
> /**
> * @return Get link configuration class
> */
> public abstract Class getLinkConfigurationClass();
> /**
> * @return Get job configuration group per direction type or null if not
> supported
> */
> public abstract Class getJobConfigurationClass(Direction jobType);
> {code}
> Here is my proposal ( if at all you want to support groups of configs, they
> atleast name the class to "ConfiguratioGroup"
> Here is how the apis makes it obvious, that this class can contain a group of
> link configs
> {code}
> /**
> * @return Get link configuration group class
> */
> public abstract Class getLinkConfigurationGroupClass();
> /**
> * @return Get job configuration group class per direction type or null if
> not supported
> */
> public abstract Class getJobConfigurationGroupClass(Direction jobType);
> {code}
> [~abec] seems to need some validation from the group on why it should be
> called "Group". I have explained my reasoning for this change in
> https://reviews.apache.org/r/26295/
> Alternatively I think the current design/ implementation to support config
> parameters grouping is overkill ( over designed)
> I prefer simple apis, less things for a developer to code and intuitive names
> to everything they represent
> 1. Remove the ConfigList and support grouping of configs by the "group"
> attribute on inputs
> 2. Have one configuration class annotation that will mandate 3 classes with
> specific annotations attributes on it FromConfig, ToConfig and LinkConfig to
> be filled.
> So having one class, gives a complete picture of all configs this connector
> uses/ provides. There is one resource bundle we require, so it maps to one
> configuration class as well.
>
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