[hibernate-dev] Hibernate Search Metadata API: Numeric and other special Field types in Hibernate Search
Hardy Ferentschik
hardy at hibernate.org
Tue Jul 16 05:19:57 EDT 2013
Ahh, and I forgot to ask Gunnar whether he thinks the API fits the OGM use case now?
--Hardy
On 16 Jan 2013, at 11:18 AM, Hardy Ferentschik <hardy at hibernate.org> wrote:
> To give some more context. The split of FieldSettingsDescriptor and FieldDescriptor is driven by the
> discussion we had regarding HSEARCH-904 and the extension of the bridge interface, allowing it
> to report the fields it creates. Custom bridges need to create or at least provide the information for the
> metadata. The idea is that they can create FieldSettingsDescriptors. The reasons of the split if that
> some information a bridge does not have access to, so it cannot and should not create it.
>
> Regarding FieldDescriptor#Type, my gut feeling is also that we should get rid of
> FieldSettingsDescriptor#isNumeric and create instead FieldDescriptor#Type.NUMERIC. This also
> implies though that the Type enum and its getter should move into FieldSettingsDescriptor as well.
> I guess that makes sense.
>
> The one thing I am wondering about is, is whether we we are not starting to mix different type concepts.
> Type.ID is not really a Lucene specific field encoding. It just says that this field has a special meaning for
> Hibernate Search, as it is the unique document id. NUMERIC, however, is a type of Lucene encoding and
> maybe there will be more. In this context, I was ordering whether SPATIAL should be another enum type.
> Initially I also thought that the Type enum could be used as well to express the opaqueness idea Emmanuel
> mentioned. An emum type of OPAQUE would then mean that this field gets generated by the bridge, but is
> opaque to the application/user. Something like this would for sure overload the current meaning of the Type enum.
>
> So maybe we need multiple enum types, but that of course increases the complexity of the API and
> already the FieldSettingsDescriptor and FieldDescriptor split is on a first glance hard to understand.
>
> Leaves the problem of additional properties based on a specific field type, e.g. precisionStep.
> I go with Gunnar and Emmanuel on this one preferring the unwrapping approach. The question is just
> wether we want to do it already now. How likely is it that we get other types?
>
> To sum up, here is what I think we need to decide on.
>
> Regarding isNumeric
> 1) Move FieldDescriptor#Type into FieldSettingsDescriptor and add a NUMERIC type (leaving us with ID, BASIC, NUMERIC)
> 2) Create a new enum (called Type or maybe better Encoding) and have NUMERIC hosted there, together with BASIC ;-)
>
> Regarding precisionsStep
> 1) Leave it as is under the assumption that there won't be many (if any) new type/encoding specific properties
> 2) Create FieldSettingsDescriptor subtypes like NumericFieldSettingsDescriptor and use the unwrap approach to
> host additional properties.
>
> Thoughts?
>
> --Hardy
>
>
>
> On 16 Jan 2013, at 9:27 AM, Gunnar Morling <gunnar at hibernate.org> wrote:
>
>> Hi,
>>
>>> I won't mention my favorite Vattern. I've considered adding subtypes
>> but not liking it as their usage would not be clear from the API.
>>
>> How would you use your vavorite Vattern without subtypes? And which other
>> option would you prefer then?
>>
>> I think the field-type specific information can either be on
>>
>> a) FieldSettingsDescriptor itself (as is today)
>> b) specific subtypes of FSD
>> c) specific delegates of FSD, safely accessible via a type parameter of FSD
>>
>> a) would IMO be the simplest but could lead to a proliferation of
>> attributes on FSD; So as you say it depends on the number of specific
>> attributes whether its feasible or not. But even if sticking to this
>> approach, we might consider to replace boolean isNumeric() with FieldType
>> getFieldType(). This would avoid adding a new isXy() method for each
>> specific type and be used like so:
>>
>> if ( desc.fieldType = NUMERIC) {
>> doSomething( desc.precisionStep() );
>> else if ( desc.fieldType = FOO ) {
>> doSomething( desc.fooAttrib() );
>> }
>>
>> For b), you need a way to narrow down to the subtype, either via Visitor or
>> some kind of cast. I still find this pattern as used in BV reads quite
>> nicely:
>>
>> Object result = null;
>> if ( desc.fieldType = NUMERIC) {
>> result = doSomething( desc.as( NumericDescriptor.class).precisionStep()
>> );
>> else if ( desc.fieldType = FOO ) {
>> result doSomething( desc.as( FooDescriptor.class).fooAttrib() );
>> }
>>
>> In particular, as() would only accept subtypes of Descriptor and be thus a
>> bit safer than a plain downcast.
>>
>> Btw., the annotation processing API (as e.g. used by the Meta model
>> generator or the AP in Hibernate Validator), offers both ways for that
>> purpose, i.e. a visitor approach and, getKind() + downcast. Having worked
>> with both, I find the usually simpler to use.
>>
>> For a comparison, the last example would look like this with a visitor
>> design similar to the annotation processing API (the type parameters are
>> for parameter and return type passed to/retrieved from the visitor):
>>
>> Object result = desc.accept(
>> new FieldDescriptorVisitor<Void, Object>() {
>>
>> @Override
>> Object visitAsNumber(NumberDescriptor descriptor, Void p) {
>> return doSomething( descriptor.precisionStep() );
>> }
>>
>> @Override
>> Object visitAsFoo(FooDescriptor descriptor, Void p) {
>> return doSomething( descriptor.fooAttrib() );
>> }
>> }
>> );
>>
>> Personally, I find this reads and writes not as nice as the other approach.
>>
>> Regarding c), one could think of something like this:
>>
>> class FieldSettingsDescriptor<T extends DescriptorSpecifics> {
>> public T getSpecifics();
>> ...
>> }
>>
>> and
>>
>> FieldSettingsDescriptor<NumberSpecifics> numberDescriptor = ...;
>> doSomething( numberDescriptor.getSpecifics().precisionStep() );
>>
>> But the question is how one would obtain a properly typed descriptor. E.g.
>> from a collection with mixed fields, one would only get
>> FieldSettingsDescriptor<?>, making this quite pointless.
>>
>> I think, I'd like the getType()/as() approach best. Or do you have yet
>> another approach in mind?
>>
>> --Gunnar
>>
>>
>>
>> 2013/7/15 Sanne Grinovero <sanne at hibernate.org>
>>
>>> The new FieldSettingsDescriptor [1] has a couple of methods meant for
>>> Numeric fields:
>>>
>>> /**
>>> * @return the numeric precision step in case this field is indexed as
>>> a numeric value. If the field is not numeric
>>> * {@code null} is returned.
>>> */
>>> Integer precisionStep();
>>>
>>> /**
>>> * @return {@code true} if this field is indexed as numeric field,
>>> {@code false} otherwise
>>> *
>>> * @see #precisionStep()
>>> */
>>> boolean isNumeric();
>>>
>>> Today we have specific support for the
>>> org.apache.lucene.document.NumericField type from Lucene, so these are
>>> reasonable (and needed to build queries) but this specific kind is
>>> being replaced by a more general purpose encoding so that you don't
>>> have "just" NumericField but can have a wide range of special fields.
>>>
>>> So today for simplicity it would make sense to expose these methods
>>> directly on the FieldSettingsDescriptor as it makes sense for our
>>> users, but then also the #isNumeric() is needed as not all fields are
>>> numeric: we're having these extra methods to accommodate for the needs
>>> of some special cases.
>>>
>>> Considering that we might get more "special cases" with Lucene4, and
>>> that probably they will have different options, would we be able to
>>> both decouple from these specific options and also expose the needed
>>> precisionStep ?
>>>
>>> I won't mention my favorite Vattern. I've considered adding subtypes
>>> but not liking it as their usage would not be clear from the API.
>>>
>>> Cheers,
>>> Sanne
>>>
>>> 1 - as merged two minutes ago
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>>> hibernate-dev at lists.jboss.org
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>>>
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