[jira] [Commented] (SIS-416) Consider adding StoreResource interface

["Martin Desruisseaux (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SIS-416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17550506#comment-17550506 ] 

Martin Desruisseaux commented on SIS-416:
-----------------------------------------

We tried to add the following method in the {{Resource}} interface, but this attempt has been cancelled:

{code:java}
    /**
     * Returns the data store that produced this resource.
     * This information allows for example to fetch the parameters used for opening the data store.
     * A resource may have no originating data store if it was generated, for example as the result
     * of a computation from other data stores.
     *
     * <p>If this resource is already a {@link DataStore}, then the value is {@code this}.</p>
     *
     * @return the data store that created this resource.
     * @throws DataStoreException if an error occurred while fetching the store.
     *         It may happen for example if the store is lazily opened.
     *
     * @since 1.3
     */
    Optional<DataStore> getOriginatingStore() throws DataStoreException;
{code}

The reason for not adding about method yet is because the contract is still unclear. Should the result of {{subset(Query)}} keep a link to the original data store? What should be the result of virtual resource such as A+B?. Instead we tried to clarify the intended contract in the internal {{StoreResource}} interface and defer the resolution to a yet later stage.


> Consider adding StoreResource interface
> ---------------------------------------
>
>                 Key: SIS-416
>                 URL: https://issues.apache.org/jira/browse/SIS-416
>             Project: Spatial Information Systems
>          Issue Type: Task
>          Components: Storage
>    Affects Versions: 0.8, 1.0, 1.1, 1.2
>            Reporter: Martin Desruisseaux
>            Assignee: Martin Desruisseaux
>            Priority: Major
>             Fix For: 1.3
>
>
> The {{org.apache.sis.storage}} package contains a {{Resource}} interface which is the root of all resources loaded by a data store ({{FeatureSet}}, {{Aggregate}}, _etc._). The resources do not tell us which data store created them. In some case we need this information, for example in order to fetch the parameters used for opening the data store.
> We could add {{getOriginatingStore()}} method in {{Resource}} interface, but not all resources are produced by a data store (a resource could be computed by a model for example). We could use an {{Optional<DataStore>}} return type, but {{Optional}} is not convenient with objects making extensive use of checked exceptions, because lambda functions are difficult to use in that context.
> A an alternative would be to define the {{getOriginatingStore()}} method in a {{StoreResource}} sub-interface, to be implemented only by resources produced by data stores. It would be the only method of that interface.
> Inconvenient of {{StoreResource}} sub-interface:
> * it is very easy to forget to implement it.
> * It is more difficult to implement by wrappers (need to prepare many sub-classes for different combination of implemented interfaces).
> * Adding a type expands the API in a more intrusive way than adding a method.
> Inconvenient of method with {{Optional<DataStore>}} return type:
> * Most {{Optional}} methods are unusable because of checked exceptions.
> * This method make little sense in {{DataStore}} (which is itself a {{Resource}}).



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