Skip to content

Extending or Modifying Blacklight Search Behavior

Jump to bottom Edit New page
Justin Coyne edited this page Apr 13, 2015 · 30 revisions

Extending or Modifying Blacklight Search Behavior

Solr parameters used by for a given request can come from several different places.

  • Solr request handler: solrconfig.xml in your solr config
  • Application logic: logic in the BL rails app itself

Solr request handler

The Solr Request Handlers may be configured in the solrconfig.xml and are baked into the request handler itself. Depending on how you have blacklight configured, your app may be using the same Solr request handler for all searches, or may be using different request handlers for different "search fields".

The request handler is often set up with default parameters:

  <requestHandler name="standard" class="solr.SearchHandler" >
     <lst name="defaults">
       <str name="echoParams">explicit</str>
       <str name="rows">10</str> 
       <str name="fl">*</str>   
       <str name="facet">true</str>
       <str name="facet.mincount">1</str>
       <str name="facet.limit">30</str> 
       <str name="facet.field">access_facet</str>
       <str name="facet.field">author_person_facet</str>
       <str name="facet.field">author_other_facet</str>
       <str name="facet.field">building_facet</str>
       <str name="facet.field">callnum_1_facet</str>
       <str name="facet.field">era_facet</str>
       <str name="facet.field">format</str>
       <str name="facet.field">geographic_facet</str>
       <str name="facet.field">language</str>
       <str name="facet.field">pub_date_group_facet</str>
       <str name="facet.field">topic_facet</str>
     </lst>
  </requestHandler>

Configuration

The default application logic (explained below) looks in configuration for things like the name of a the solr request handler to use, and default request parameters to send on every solr search request (or with every request from a certain blacklight search type/field). An example getting started configuration is generally installed into your app when you install Blacklight at ./app/controllers/catalog_controller.rb.

Application logic

The logic Blacklight uses to determine how to map user-supplied parameters into Solr request parameters for a given application request is in the #processed_parameters method in the SearchBuilder class. Note that CatalogController includes SearchHelper, so the SearchHelper methods become available in the CatalogController (and other classes, if they include SearchHelper too).

Behind the scenes, SearchBuilder#processed_parameters uses the class_inheritable_accessor method search_params_logic. search_params_logic is essentially a class variable that is mixed into the CatalogController and provides an ordered list of methods to call that may inspect the supplied user parameters and add, remove, or modify the Solr request parameters that will be sent to an RSolr object, which in turn will convert the hash into query parameters for a Solr request. One confusing thing is that RSolr and RSolr-ext provide their own mappings from certain custom terms to Solr-recognized request parameters. For instance, a :per_page key in that hash will get mapped to the Solr &rows parameter -- but a :rows key will also. Blacklight developers have found that using these special RSolr "aliases" leads to confusion, as well as confusing bugs (if both :per_page and :rows are set in the hash, what happens can be hard to predict). So we try to avoid using the special RSolr aliases, and just use ordinary Solr parameters in our hashes. But you may encounter older code that uses the RSolr aliases.

There can be similar confusing behavior or bugs if one piece of code adds a key to a Hash using a Symbol, but another piece of code looks for and/or adds that same key to the Hash using a String instead. RSolr happens to accepts either one, but if both are present RSolr behavior can be unexpected. And even before it gets to RSolr, you may have code that thinks it replaced a key but did not becuase it was using the wrong form. Blacklight developers have agreed to try and always use Symbol based keys in hashes meant for Solr parameters, to try and avoid these problems. Longer term, we could probably make some code changes to make this kind of error less likely.

The default #search_params_logic is meant to handle very common cases and patterns based on simple configuration options from the controller and the user-supplied URL parameters.

  • blacklight_config.default_solr_params
    • Default params sent to solr with every search, including the default :qt param, which determines which Solr request handler will be targetted. Some people like to use solrconfig.xml request handler defaults exclusively, and include only a :qt here; others find it more convenient to specify some defaults at the application level here.
  • blacklight_config.search_fields
    • Each search field will be presented in a select menu in the BL user interface search box. These 'search fields' don't neccesarily correspond 1-to-1 with Solr fields. What they instead correspond to is Solr parameter over-rides that will be used for this BL UI search field. Those over-rides are present here.
    • You could simply chose a different :qt Solr request handler for each search field, which has it's own default parameters in the sorlconfig.xml. This is what we started out doing with Solr, but found it led to much duplication of information in solrconfig.xml.
    • You can continue using the same Solr request handler, but simply specify different parameters which will be included in the http query string sent to Solr here, with the :solr_parameters key. This works fine, but some people don't like how it makes your Solr requests much longer/more complex in the Solr logs; and/or they prefer to control this Solr side instead of Application side.
    • For the best of both worlds, although it's a bit confusing at first, you can use the :solr_local_parameters key to have parameters supplied to Solr using the Solr LocalParams syntax, which means you can use "parameter dereferencing" with dollar-sign-prefixed references to variables defined in solrconfig.xml request handler. This is what the current example BL setup does.

So the default implementation of SearchBuilder takes these configured parameters, combines them with certain query parameters from the current users HTTP request to the BL app, and prepares a query that will be sent to solr. For common use patterns, this is all you need.

But sometimes you want to add some custom logic to #search_params_logic to come up with the solr parameters in different ways. Typically to support a new UI feature of some kind, either in your local app or in a Blacklight add-on plugin you are developing.

Extending Blacklight::SearchHelper#search_params_logic

To add new search behaviors (e.g. authorization controls, pre-parsing query strings, etc), the easiest route is to add additional steps to the #search_params_logic, either at the beginning of the list (to set default parameters) or at the end of the list (to force particular parameters). Because #search_params_logic is just an ordinary array, you may perform any normal array operation (e.g. push/pop/delete/insert) to customize the parameter generation to meet your needs.

#search_params_logic steps take one argument: the hash of solr_parameters and modifies the solr_parameters directly, as needed. The SearchBuilder class also provides a blacklight_parameters hash, which conatains the user provided parameters (from the URL parameters),

You can add custom search_params_logic steps within your CatalogController by adding a Symbol with the name of a method (provided by SearchBuilder) you wish to use, e.g.:

# ./app/controllers/catalog_controller.rb
class CatalogController  < ApplicationController 
  include Blacklight::Catalog
  self.search_params_logic += [:show_only_public_records]
end

Then implement the method in your SearchBuilder

# ./app/models/search_builder.rb

class SearchBuilder < Blacklight::SearchBuilder
  include Blacklight::Solr::SearchBuilderBehavior
  
  # @param [Hash] solr_parameters a hash of parameters to be sent to Solr (via RSolr)
  def show_only_public_records solr_parameters
    # add a new solr facet query ('fq') parameter that limits results to those with a 'public_b' field of 1 
    solr_parameters[:fq] ||= []
    solr_parameters[:fq] << 'public_b:1'
  end
end

Other examples

In addition to providing this behavior locally, some Blacklight plugins also extend the #search_params_logic:

Suppressing search results

You can configure your solrconfig.xml to not show results based on fields in your solr document. For example, if you have a solr boolean field such as show_b, you can suppress any records that have this field present. To do so, add:

<lst name="appends"><str name="fq">-show_b:["" TO *]</str></lst>

to the request handler in your solrconfig.xml file. If you would like this to be for standard solr searches, add the above line to this request handler:

<requestHandler name="search" class="solr.SearchHandler" default="true">

By doing so, solr queries that use the "document" request handler will still give you any records with the show_b field, but solr queries with the "search" handler will not.

Add a custom footer

Quickstart Guide

Upgrading to Blacklight 8

Demo

Example installations

Blacklight Summits and Events

Clone this wiki locally