[jira] Assigned: (SOLR-1149) Make QParserPlugin and related classes extendible

["Shalin Shekhar Mangar (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SOLR-1149?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Shalin Shekhar Mangar reassigned SOLR-1149:
-------------------------------------------

    Assignee: Shalin Shekhar Mangar

> Make QParserPlugin and related classes extendible
> -------------------------------------------------
>
>                 Key: SOLR-1149
>                 URL: https://issues.apache.org/jira/browse/SOLR-1149
>             Project: Solr
>          Issue Type: Improvement
>          Components: search
>            Reporter: Kaktu Chakarabati
>            Assignee: Shalin Shekhar Mangar
>             Fix For: 1.4
>
>         Attachments: SOLR-1149.patch
>
>
> In a recent attempt to create a QParserPlugin which extends DisMaxQParser/FunctionQParser functionality, 
> it became apparent that in the current state of these classes, it is not straight forward and in fact impossible to seriously build
> upon the existing code. 
> To this end, I've refactored some of the involved classes which enabled me to reuse existing logic to great results.
> I thought I will share these changes and comment on their nature in the hope these will make sense to other solr developers/users, and
> at the very least cultivate a fruitful discussion about this particular area of the solr codebase.
> The relevant changes are as follows:
> * Renamed DismaxQParser class to DisMaxQParser ( in accordance with the apparent naming convention, e.g DisMaxQParserPlugin )
> * Moved DisMaxQParser to its own .java file, making it a public class rather than its previous package-private visibility. This makes
>   it possible for users to build upon its logic, which is considerable, and to my mind is a good place to start alot of custom
>   QParser implementations.
> * Changed access modifiers for the QParser abstract base class to protected (were package-private). Again as above, it makes this
>   object usable by user-defined classes that wish to define custom QParser classes. More generally, and on the philosophy-of-code 
>   side of things, it seems misleading to define some class members as having the default access modifier (package-private) and then
>   letting other package-scope derived classes use these while not explicitly allowing user-defined derived classes to make use of these members.
>   In specific i'm thinking of how DisMaxQParser makes use of these members: **not because it is derived from QParser, but because it
>   simply resides in the same namespace**
> * Changed access modifier for the QueryParsing.StrParser inner class and its constructors to public. Again as in above, same issue
>   of having same-package classes enjoy the benefit of being in the same namespace (FunctionQParser.parse() uses it like so), 
>   while user defined classes cannot. Particulary in this case it is pretty bad since this class advertises itself as a collection of utilities
>   for query parsing in general - great resource, should probably even live elsewhere (common.utils?)
> * Changed Function.FunctionWeight inner class data member modifiers to protected (were default - package-private). This allowed me
>   to inherit from FunctionQuery as well as make use of its original FunctionWeight inner class while overriding some of the latter's
>   methods. This is in the same spirit of the changes above. Please also note this follows the common Query/Weight implementation pattern
>   in the lucene codebase, see for example the BooleanQuery/BooleanWeight code.
> All in all these are relatively minor changes which unlock a great deal of functionality to 3rd party developers, which i think is
> ultimately a big part of what solr is all about - extendability. It is also perhaps a cue for a more serious refactoring of the
> QParserPlugin hierarchy, although i will leave such bold exclamations to another occasion.
> Attached is a patch file, having passed the usual coding-style/unit testing cycle.
> -Chak

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