Solr integration

[etj]

The code removed in this commit made the plugin compatible again vs solr 6.x.

Where does the code come from? Is it a backport from latest ckan? Is it needed for some special solr version?

[etj]

The code does work with Solr 4.5.0 (for instnace on dcatapit.geo-solutions.it)

[cezio]

The change was because otherwise facet filtering from #87 and #86 wouldn't work correctly with ckan 2.5.7 + solr 7.0.

Solr uses OR operator for fields in fq as default. I found that ckan will prepend value of fq with capacity:"public" in https://github.com/ckan/ckan/blob/ckan-2.5.7/ckan/logic/action/get.py#L1920
causing whole query returning all datasets when used with facet search:

capacity:"public" organization_region:"sardegna" +dataset_type:dataset -dataset_type:harvest

which translates roughtly into

capacity:"public" OR organization_region:"sardegna" AND dataset_type:dataset NOT dataset_type:harvest

This will produce invalid query result, returning all datasets instead of one:

<?xml version="1.0" encoding="UTF-8"?>
<response>

<lst name="responseHeader">
  <int name="status">0</int>
  <int name="QTime">0</int>
  <lst name="params">
    <str name="q">*:*</str>
    <str name="fq">capacity:"public" organization_region:"sardegna" +dataset_type:dataset -dataset_type:harvest</str>
    <str name="_">1518709559156</str>
  </lst>
</lst>
<result name="response" numFound="251" start="0">

When my fix was in use, query was with additional +, so query params were joined with AND

capacity:"public" +organization_region:"sardegna" +dataset_type:dataset -dataset_type:harvest

capacity:"public" AND organization_region:"sardegna" AND dataset_type:dataset NOT dataset_type:harvest

<?xml version="1.0" encoding="UTF-8"?>
<response>

<lst name="responseHeader">
  <int name="status">0</int>
  <int name="QTime">0</int>
  <lst name="params">
    <str name="q">*:*</str>
    <str name="fq">capacity:"public" +organization_region:"sardegna" +dataset_type:dataset -dataset_type:harvest</str>
    <str name="_">1518709559156</str>
  </lst>
</lst>
<result name="response" numFound="1" start="0">

I'm not sure why this didn't work with solr 6.x. Do I understand correctly, my change is working correctly with solr 4.5? which ckan version you were using?