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Solr search

  • This module provides an implementation of the Search API which uses an Apache
    Solr search server for indexing and searching. You can find detailed
    instructions for setting up Solr in the module's handbook [1].



  • Install this module using the official Backdrop CMS instructions at

  • As the only pre-requisite you will need the Search API [1] module enabled and
    correctly set up, as well as the Entity Plus [2] module enabled.



Supported optional features

  • All Search API datatypes are supported by using appropriate Solr datatypes for
    indexing them. By default, "String"/"URI" and "Integer"/"Duration" are defined
    equivalently. However, through manual configuration of the used schema.xml this
    can be changed arbitrarily. Using your own Solr extensions is thereby also

  • The "direct" parse mode for queries will result in the keys being directly used
    as the query to Solr. For details about Lucene's query syntax, see [2]. There
    are also some Solr additions to this, listed at [3]. Note however that, by
    default, this module uses the dismax query handler, so searches like
    "field:value" won't work with the "direct" mode.


Regarding third-party features, the following are supported:

  • search_api_autocomplete
    Introduced by module: search_api_autocomplete
    Lets you add autocompletion capabilities to search forms on the site. (See
    also "Hidden variables" below for Solr-specific customization.)

  • search_api_facets
    Introduced by module: search_api_facetapi
    Allows you to create facetted searches for dynamically filtering search

  • search_api_facets_operator_or
    Introduced by module: search_api_facetapi
    Allows the creation of OR facets.

  • search_api_mlt
    Introduced by module: search_api_views
    Lets you display items that are similar to a given one. Use, e.g., to create
    a "More like this" block for node pages.
    NOTE: Due to a regression in Solr itself, "More like this" doesn't work with
    integer and float fields in Solr 4 versions lower than 4.6. As a work-around,
    you can index the fields (or copies of them) as string values. See [4] for
    Also, MLT with date fields isn't currently supported at all for any version.

  • search_api_multi
    Introduced by module: search_api_multi
    Allows you to search multiple indexes at once, as long as they are on the same
    server. You can use this to let users simultaneously search all content on the
    site – nodes, comments, user profiles, etc.

  • search_api_spellcheck
    Introduced by module: search_api_spellcheck
    Gives the option to display automatic spellchecking for searches.

  • search_api_data_type_location
    Introduced by module: search_api_location
    Lets you index, filter and sort on location fields. Note, however, that only
    single-valued fields are currently supported for Solr 3.x.

  • search_api_grouping
    Introduced by module: search_api_grouping [5]
    Lets you group search results based on indexed fields. For further information
    see the FieldCollapsing documentation in the solr wiki [6].



Please consider that, since Solr handles tokenizing, stemming and other
preprocessing tasks, activating any preprocessors in a search index' settings is
usually not needed or even cumbersome. If you are adding an index to a Solr
server you should therefore then disable all processors which handle such
classic preprocessing tasks. Enabling the HTML filter can be useful, though, as
the default config files included in this module don't handle stripping out HTML

Clean field identifiers:
If your Solr server was created in a module version prior to 1.2, you will get
the option to switch the server to "Clean field identifiers" (which is default
for all new servers). This will change the Solr field names used for all
fields whose Search API identifiers contain a colon (i.e., all nested fields)
to support some advanced functionality, like sorting by distance, for which
Solr is buggy when using field names with colons.
The only downside of this change is that the data in Solr for these fields
will become invalid, so all indexes on the server which contain such fields
will be scheduled for re-indexing. (If you don't want to search on incomplete
data until the re-indexing is finished, you can additionally manually clear
the indexes, on their Status tabs, to prevent this.)

Hidden variables

  • search_api_solr_autocomplete_max_occurrences (default: 0.9)
    By default, keywords that occur in more than 90% of results are ignored for
    autocomplete suggestions. This setting lets you modify that behaviour by
    providing your own ratio. Use 1 or greater to use all suggestions.

  • search_api_solr_index_prefix (default: '')
    By default, the index ID in the Solr server is the same as the index's machine
    name in Backdrop. This setting will let you specify a prefix for the index IDs
    on this Backdrop installation. Only use alphanumeric characters and underscores.
    Since changing the prefix makes the currently indexed data inaccessible, you
    should change this vairable only when no indexes are currently on any Solr

  • search_api_solr_http_get_max_length (default: 4000)
    The maximum number of bytes that can be handled as an HTTP GET query when
    HTTP method is AUTO. Typically Solr can handle up to 65355 bytes, but Tomcat
    and Jetty will error at slightly less than 4096 bytes.

  • search_api_solr_cron_action (default: "spellcheck")
    The Search API Solr Search module can automatically execute some upkeep
    operations daily during cron runs. This variable determines what particular
    operation is carried out.

  • spellcheck: The "default" spellcheck dictionary used by Solr will be rebuilt
    so that spellchecking reflects the latest index state.

  • optimize: An "optimize" operation [8] is executed on the Solr server. As a
    result of this, all spellcheck dictionaries (that have "buildOnOptimize" set
    to "true") will be rebuilt, too.

  • none: No action is executed.
    If an unknown setting is encountered, it is interpreted as "none".

  • search_api_solr_site_hash (default: random)
    A unique hash specific to the local site, created the first time it is needed.
    Only change this if you want to display another server's results and you know
    what you are doing. Old indexed items will be lost when the hash is changed
    and all items will have to be reindexed. Can only contain alphanumeric

  • search_api_solr_highlight_prefix (default: "tm_")
    The prefix of Solr fields for which field-level highlighting will be enabled.
    Since the prefix of fields is used to determine the field type (by default),
    this lets you enable highlighting for other field types. By default,
    highlighting will be possible for all fulltext fields.

  • search_api_solr_connection_class (default: "SearchApiSolrConnection")
    The connection class to use for connecting to Solr. Needs to implement


Customizing your Solr server

The schema.xml and solrconfig.xml files contain extensive comments on how to
add additional features or modify behaviour, e.g., for adding a language-
specific stemmer or a stopword list.
If you are interested in further customizing your Solr server to your needs,
see the Solr wiki at [9] for documentation. When editing the schema.xml and
solrconfig.xml files, please only edit the copies in the Solr configuration
directory, not directly the ones provided with this module.


You'll have to restart your Solr server after making such changes, for them to
take effect.


The SearchApiSolrService class has a few custom extensions, documented with its
code. Methods of note are deleteItems(), which treats the first argument
differently in certain cases, and the methods at the end of

Also, when requesting facets with a search, you can use the custom
"solr_facet_query" key in the facet options to pass an array of facet queries to
Solr, which should be used instead of the default "facet.field" parameter. The
facet queries will automatically have "FIELD:" prepended to them. The returned
facets will have an additional "solr_facet_query" key in addition to "filter"
and "count", to spot them more easily.

Current Maintainers



This project is GPL v2 software.
See the LICENSE.txt file in this directory for complete text.