[jira] [Commented] (AVRO-839) Implement builder pattern in generated record classes that sets default values when omitted

["James Baldassari (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AVRO-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13082917#comment-13082917 ] 

James Baldassari commented on AVRO-839:
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Sorry for the long delay in working on this.  I finally had a chance to get back to it this week, and I have another patch ready.  The main changes are:

* Moved Builder-related interfaces and base classes out of top-level package into org.apache.avro.data
* Getters/setters get/set fields directly rather than calling get()/put()
* In an effort to improve overall builder performance for specific/generated records, I moved most of the generic code out of RecordBuilderBase and pushed it down into the generated Builder code.  I also did quite a bit of profiling in an effort to reduce the biggest bottlenecks.
** There is now a lot more generated code, but it's faster.
** Testing indicates that without using default values (i.e. all fields in the Builder are set), the Builder is about one order of magnitude slower than directly creating/initializing a record.  However, a Builder instance can be reused, and if this is done rather than creating a new Builder each time there is almost no performance penalty for using the Builder.
** If the Builder has to resolve a default value from the schema, it's obviously going to be a little slower, but it's still only one order of magnitude slower than directly creating records.  In my testing the Builder was about 3-4 times slower when resolving default values, but I expect this will vary a lot depending on the schema.

So let me know what you think.  I'm happy to make more adjustments if necessary.

> Implement builder pattern in generated record classes that sets default values when omitted
> -------------------------------------------------------------------------------------------
>
>                 Key: AVRO-839
>                 URL: https://issues.apache.org/jira/browse/AVRO-839
>             Project: Avro
>          Issue Type: Improvement
>          Components: java
>            Reporter: James Baldassari
>            Assignee: James Baldassari
>         Attachments: AVRO-839-v2.patch, AVRO-839-v3.patch, AVRO-839.patch
>
>
> This is an idea for an improvement to the SpecificCompiler-generated record classes.  There are two main issues to address:
> # Default values specified in schemas are only used at read time, not when writing/serializing records.  For example, a NullPointerException is thrown when attempting to write a record that has an uninitialized array or string type.  I'm sure this was done for good reasons, like giving users maximum control and preventing unnecessary garbage collection, but I think it's also somewhat confusing and unintuitive for new users (myself included).
> # Users have to create their own factory classes/methods for every record type, both to ensure that all non-primitive members are initialized and to facilitate the construction and initialization of record instances (i.e. constructing and setting values in a single statement).
> These issues have been discussed previously here:
> * [http://search-hadoop.com/m/iDVTn1JVeSR1]
> * AVRO-726
> * AVRO-770
> * [http://search-hadoop.com/m/JuY1V16pwxh1]
> I'd like to propose a solution that is used by at least one other messaging framework.  For each generated record class there will be a public static inner class called Builder.  The Builder inner class has the same fields as the record class, as well as accessors and mutators for each of these fields.  Whenever a mutator method is called, the Builder sets a boolean flag indicating that the field has been set.  All mutators return a reference to 'this', so it's possible to chain a series of setter invocations, which makes it really easy to construct records in a single statement.  The Builder also has a build() method which constructs a record instance using the values that were set in the Builder.  When the build() method is invoked, if there are any fields that have not been set but have default values as defined in the schema, the Builder will set the values of these fields using their defaults.
> One nice thing about implementing the builder pattern in a static inner Builder class rather than in the record itself is that this enhancement will be completely backwards-compatible with existing code.  The record class itself would not change, and the public fields would still be there, so existing code would still work.  Users would have the option to use the Builder or continue constructing records manually.  Eventually the public fields could be phased out, and the record would be made immutable.  All changes would have to be done through the Builder.
> Here is an example of what this might look like:
> {code}
> // Person.newBuilder() returns a new Person.Builder instance
> // All Person.Builder setters return 'this' allowing us to chain set calls together for convenience
> // Person.Builder.build() returns a Person instance after setting any uninitialized values that have defaults
> Person me = Person.newBuilder().setName("James").setCountry("US").setState("MA").build();
> // We still have direct access to Person's members, so the records are backwards-compatible
> me.state = "CA";
> // Person has accessor methods now so that the public fields can be phased out later
> System.out.println(me.getState());
> // No NPE here because the array<Person> field that stores this person's friends has been automatically 
> // initialized by the Builder to a new java.util.ArrayList<Person> due to a @java_class annotation in the IDL
> System.out.println(me.getFriends().size());
> {code}
> What do people think about this approach?  Any other ideas?

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