Add Support For Composite Keys

[natemacinnes]

Currently the schema only handles a single primary key.

def primary_key_for(entity_name)
  metadata.xpath("//EntityType[@Name='{entity_name}']/Key/PropertyRef").first.attributes['Name'].value
     end

The OData specification supports composite keys, i.e.,

<EntityType Name="RetailTransaction">
    <Key>
        <PropertyRef Name="dataAreaId" />
        <PropertyRef Name="TransactionNumber" />
        <PropertyRef Name="OperatingUnitNumber" />
        <PropertyRef Name="Terminal" />
    </Key>
...
</EntityType>

Not entirely sure of the best approach of handling this just yet, but starting with checking if all keys defined for the Entity in the schema are present before asserting whether the Entity is new or not is probably a good place to start.

[PandaWhisperer]

Hi @natemacinnes, thanks for submitting this issue. That's indeed a good and useful feature request. However, our current needs do not include composite keys, and I have no services to test this against.

However, if you can get this working I'd be happy to review your pull request, and I'll try and give you all the assistance I can to make it work.

Please note that I'm renaming the gem to frodata, and development will continue there. The latest version also includes quite a few changes, including using Faraday as the transport layer.

I'm leaving this repo up for the time being in order to preserve history, but no new commits will be made here (except updating the README).

[PandaWhisperer]

Sorry, I didn't mean to close this issue.

[natemacinnes]

No worries, I am no longer working for the agency that required OData4 so I will probably not continue development of this. Perhaps my successor on the project will; we shall see.