Added support for custom query option implementation with a simple extension handler

[DevKrieger]

This adds a simple IODataQueryOptionsBindingExtension interface that allows third-party libraries to extend the ApplyTo method in the ODataQueryOptions class.

Example:

Add a custom handler and extend the queryable.

 public class ExampleQueryOptionsBindingExtension : IODataQueryOptionsBindingExtension
    {
        public IQueryable ApplyTo(IQueryable query, ODataQueryOptions queryOptions, ODataQuerySettings querySettings)
        {
            //Do something here
            return query;
        }
    }

Add the extension handler to a service collection of a route component.

.AddRouteComponents("v1", model1, (services) =>
{
    services.AddDataQueryOptionsBindingExtension(new ExampleQueryOptionsBindingExtension());
})

[ghost]

All CLA requirements met.

[corranrogue9]

I don't think I understand why extensions is a delegate instead of just the extensions themselves. What's the reasoning behind this?

[DevKrieger]

Personally I like it more this way because I think it looks better in the configuration :). But it can also be changed if you don't like this approach.

.AddRouteComponents("v1", model1, (services) =>
{
    services.AddMultipleODataQueryOptionsBindingExtension((extensions) =>
    {
        extensions.Add(new ExampleQueryOptionsBindingExtension());
        extensions.Add(new Example1QueryOptionsBindingExtension());
        extensions.Add(new Example2QueryOptionsBindingExtension());
        extensions.Add(new Example3QueryOptionsBindingExtension());
    });
})

[corranrogue9]

I'm not sure yet if I'm nitpicking or not :), but I think then wouldn't the delegate be Func<IEnumerable<IODataQueryOptionsBindingExtension>, IEnumerable<IODataQueryOptionsBindingExtension>> extensions so that you could write:

.AddRouteComponents("v1", model1, (services) =>
{
    services.AddMultipleODataQueryOptionsBindingExtension((extensions) =>
    {
        extensions
          .Append(new ExampleQueryOptionsBindingExtension())
          .Append(new Example1QueryOptionsBindingExtension())
          .Append(new Example2QueryOptionsBindingExtension())
          .Append(new Example3QueryOptionsBindingExtension());
    });
})

In fact, though, before I waste too much of your time, @xuzhg are you alright with the structure of this change? If so, I'll go ahead and start reviewing more, but I want to make sure we are heading in the right direction first.

[DevKrieger]

@corranrogue9 Your solution is also fine, both should work :)

[corranrogue9]

Can you please add some tests for this new feature?

[DevKrieger]

I have added some tests.

[habbes]

I think this is a great feature being introduced. Given that this introduces a new API, I think I'd like to see more discussions/thoughts on design considerations. @xuzhg @corranrogue9 @gathogojr any thoughts on this.

@DevKrieger is this PR linked to an existing issue? If so, could you link the issue? If not, could you create an issue that describes what the problem being solved, that feature being requested?

Before reading the code, I'd like to understand what the expected behavior, what the specification for this feature is. e.g. at what point of the query transformation pipeline is this customer handler invoked, and where does its result get applied? Is the extension expected to be able to modify the query settings and query options objects? If so, what's the impact, if not, should do we do anything to prevent that from happening?

[wachugamaina]

Please provide some documentation for Public classes, functions and methods.

[wachugamaina]

What are these params used for ?

[wachugamaina]

Is the intention here to return the last result and ignore the rest ?

[wachugamaina]

Prefer to use var for consistency.

[wachugamaina]

Prefer to use var for consistency.