Implement multi select faceting

[janezomgzomg]

PR created for visibility. This is currently implemented only in field facets.

Basics

• A multi-select filter facet can be removed and added. The resultant fq is added to the search query and the results are returned and displayed.
• Added a LocalParamsService.
  • getLocalParams: processes responseHeader.params and returns the localParams for the various facet types. Only field and range is supported in this service.
  • getLocalParamTag: returns the tag that is present in the facet object
• tag is set for each individual facet in facetList. This is retrieved from responseHeader.params and is processed in LocalParamsService.
• facet-tag/facetTag is passed into facetFieldDirective from facetList as a scope variable.
• registered keyValue, join, wrapper transformers for localParams
  • keyValue -> localParamKeyValTransformer: generates the basic keyVal for the filter query. {!tag=dc}parsing_time_l:("10")
  • join -> localParamJoinTransformer: modifies the existing fq with the newly added/removed filter value. {!tag=dc}parsing_time_l:("10" OR "11")
  • wrapper -> localParamWrapperTransformer: stringifies the filter value

    Adding a filter

• tag is set in the keyObj in addQueryFacet. It can be either the tag value or null.
• If tag exists, the query facet will be assigned:
  • key = {!tag=tagname} + key
  • transformer = localParams
• If the query facet exists, the new values are pushed into the values object of the query facet. A duplicate query facet will not be added.
• checkIfMultiSelectFQExists() checks if a query facet exists with the keyname and the tag specified.

  Removing a filter

• Check if the facet has key && fq:field || {!tag=tagname}key && localParams to remove the correct filter.

  Query Builder

• getTransformerFn can now handle an array of transformers. See EDIT.

  TODO:

• [x] Implement in field facets
• [ ] Implement in range facets - will be done separately
• [ ] Document QueryBuilder changes - none to make after EDIT

  EDIT:

• Moved the snippet of determining the transformer from an array of transformers into a gist for later use. https://gist.github.com/janezomgzomg/33b4b2b96d6ec4bfb4c4337345e44a4a

[JoshEllinger]

@janezomgzomg looks great mostly, Could use more comments, and moving code around to make organization better. But overall looks great.

[janezomgzomg]

@JoshEllinger I've made the requested changes and added comments. I've updated the PR description.

[JoshEllinger]

I do have some ideas on how to make this code cleaner, and more scalable to other situations. But in interests of getting something in, i think this looks fine, as it works.

In the future, i think it makes more sense not to use localParams syntax at all outside of querybuilder, which should handle all syntax issues. Also appending tag in front of keys is probably an unnecessary constraint, and has the possibility affect some untested edge cases.

@janezomgzomg great job on a tough part of View and solr 🚀