Fetching $metadata for a specific collection or en

Question

The environment

As part of an integration project, I need a PHP website to be able to both read from and write to Microsoft Dynamics NAV 2016's Odata services.

Microsoft Dynamics NAV 2016 uses the Odata v3 standard.

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The context

Now, let's take my customer service as an example.

Fetching a collection of entities

Fetching an overview of my collection of customer entities works fine, using a link with the following format :

https://<Server>:<WebServicePort>/<ServerInstance>/OData/Company(\'<CompanyName>\')/customer

Fetching a single entity

Fetching a single customer entity based on id works fine, using a link with the following format :

https://<Server>:<WebServicePort>/<ServerInstance>/OData/Company(\'<CompanyName>\')/customer(\'<Id>\')

Fetching the global metadata

Getting an overview of the $metadata for all of my services works fine (although it's lacking Json support), using a link with the following format :

https://<Server>:<WebServicePort>/<ServerInstance>/OData/$metadata

Fetching collection-specific metadata

Now, based on both the Odata v3 specs and the value of the odata.metadata property of my customer overview service, I would expect to be able to get an overview of the $metadata of the customer entity, using a link with the following format :

https://<Server>:<WebServicePort>/<ServerInstance>/OData/$metadata#customer

This doesn't work as expected. See sub-section The issue below.

Fetching entity-specific metadata

Similarly, based on both the Odata v3 specs and the value of the odata.metadata property of my dataset when retrieving a single customer, I would expect to be able to get an overview of the $metadata of a single field of the customer entity, using a link with this format :

https://<Server>:<WebServicePort>/<ServerInstance>/OData/$metadata#customer/@<FieldName>

This doesn't work as expected. See sub-section The issue below.

The issue

For some reason, everything following $metadata appears to be ignored. This means that the last three URLs give me the exact same output, which is not what I expected.

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The actual question(s)

• Is it possible to fetch the metadata of just one collection or entity, as I'm trying in sub-sections Fetching collection-specific metadata and Fetching entity-specific metadata of my The context section hereabove?
• If yes, what I doing wrong here? What am I missing?

Answer 1

As @xuzhg suggested in the comments and as is indicated by Github issues like Support Metadata as a service (#181), it appears that the Odata $metadata are not really a dynamic service. Instead, it's just a single XML file.

This explains not only why anything after $metadata is ignored in links of format https://<Server>:<WebServicePort>/<ServerInstance>/OData/$metadata#..., but also why it only supports XML, and not Json (unlike actual Odata services).

Answer 2

Since the specific metadata you want is identified by a fragment appended to the metadata URI, you must fetch the entire $metadata document and then dereference the fragment on the client.

The good news is that the fragment dereferencing is pretty straightforward. A fragment like #customer specifies an EntityType element whose Name attribute has the value customer. Similarly, #customer/@someprop maps to a Property element whose Name attribute is someprop.