Parsing OData - service operations

Published on 2013-4-9

As well as addressing resources and resource paths, in OData we apparently have the ability to invoke "service operations" as well.

From what I see, these are addressed in a pretty much identical manner to actual resources like so

/ProductsByColor?color='red'

Or

/ProductsByColor(3)/Category/Name?color='red'

The invocation on the server is the same in each of these cases, however in the second case we're addressing into the collection returned by the invocation.

Now, a simple solution to this will be to carry on using the existing parser, and supply these custom params as part of the overall model:

So, with the following test:

test("/method(1)/child?foo=bar", function(result) {
  it("should have the resource specified", function() {
     assert.equal(result.resource, 'method')
  })
  it("The result should be addressed", function() {
     assert.equal(result.key, '1')
  })

  it("should have the path specified", function() {
     assert.equal(result.next.resource, 'Child')
  })

  it("should have the argument specified", function() {
     assert.equal(result.args.foo, 'bar')
  })
})

I might then solve it by simply adding this to the end of my main expression

OData = (
  (
    PathSegment:model 
    (
      '?'
      OperationParam:param
    )?

Where

OperationParam = 
  Text:name '=' Text:value -> { name: name, value: value }
,

(Text is a hack so I'm not putting that here until I've defined what it actually is - similar to my kerfuffle over resource names earlier)

To build up the model we can do some inline code like so:

OData = (
  (
    PathSegment:model 
    (
      '?'
      OperationParam:param
    )?
  ) -> { 
          if(param) {
           model.args = {}
           model.args[param.name] = param.value;
          }
         return model
       }
  | '/'
) 

This will have the desired effect to an extent, of course it won't pass this test:

test("/method(1)/child?foo=bar&foz=baz", function(result) {
  it("should have 'foo' specified", function() {
     assert.equal(result.args.foo, 'bar')
  })
  it("should have 'foz' specified", function() {
     assert.equal(result.args.foz, 'baz')
  })
})

This is where the built-in 'listOf' comes in useful:

OData = (
  (
    PathSegment:model 
    (
      '?'
      listOf(`OperationParam, '&'):params
    )?

With an appropriate loop to build up the list

OData = (
  (
    PathSegment:model 
    (
      '?'
      listOf(`OperationParam, '&'):params
    )?
  ) -> { 
          if(params) {
           model.args = {}
           for(var i in params)
             model.args[params[i].name] = params[i].value;
          }
         return model
       }
  | '/'
) 

Now, a few things getting wrong with this whole implementation so far...

I can live most of this for now - but I've made a note that they're making me uncomfortable so when my progress is at a suitable point I can deal with them.

2015 © Rob Ashton. ALL Rights Reserved.