add ResultLimit feature, implements ideas from #29

[benib]

this implements some things discussed in issue #29.
default is to return all fields. if fields parameter is set, only the defined fields are returned as long as there is a check in the code, where the field is added to the result. this can be done like:

if (ResultLimit::includeField('from')) {
    // add from stuff to result
}

these checks are implemented in Transport\Entity\Schedule\Connection for the fields "from", "to" and "journey" to show how this works.

Tree like fields are also possible, eg:

http://sbb.local/v1/connections?from=008501120&to=008501008&fields[]=to&fields[]=from/geo

in that case, ResultLimit::includeField('from') returnes true, as there is a more specific field set.

any comments are appreciated.

[rndstr]

Quick feedback:

• Why not make everything static in ResultLimit, get rid of the Singleton, and add a private ctor? Although I would prefer seeing it as an instance passed around or even better pass the $request somehow. Haven't yet thought it through, though.
• You should put open parentheses of classes and methods on their own line (see rest of codebase)
• Tests? ;)

[benib]

• i agree about making everything static.
• also agree about coding styles
• personally i like the approach with the static function includeField(), that way, we can just add this call where some data is added to the request and don't have to worry about passing instances around. the information which fields to include is static and only set once with the request sent to the API.

[rndstr]

I suggest doing type hinting here array $fields instead of the is_array() check below

[benib]

@rndstr: i sticked to isFieldSet as isFieldIncluded seems to be confusing to me, as the field is not yet included, we want to know if it should be or not.

[rndstr]

Thanks for the changes! I'm okay with ResultLimit being static for now I guess.

But looking at the code, I see you are only checking for the from, to and journey parts in the Connection resource. What is your idea about the other resources and their fields?

[benib]

• checks are now implemented for /connections and /stationboard
• if no fields are set, everything is returned
• if any field is set, only the specified fields are returned
• fields are specified in a path like model
• if eg. connections/from is set, only the from element and everything below is returned
• if eg. connections/from/station is set, only the from element containing only the station is returned
• this can be combined to something like fields[]=connections/from/station&fields[]=connections/to/arrival

[fabian]

Merged, thanks!