Allows querying the XWiki Model using a variety of query languages

Description

All data making up the XWiki application can be queried using one of the supported Query languages. Right now we support 3 languages:

• XWiki Query Language (XWQL)
• Hibernate Query Language (HQL)
• Solr Query Langage (SOLR)

Historically XWiki was only supporting HQL but that lead to complex queries in some instances and thus we've introduced XWQL which is a JPQL superset and which makes it much easier to write queries for the XWiki model, as you can see in the examples below.

Query Language Examples

See also examples of queries at https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-oldcore/src/main/resources/queries.hbm.xml

Performing Queries

The principle is to get a reference to the Query Manager, then call a method on it to create a Query for a given Query language. Then on the Query object you can set some behaviors (limit the number of returned result, bind variables, set the offset, set the wiki on which to execute the query) and then execute it.

From Velocity

For XWQL:

• Return all the results matching the XWQL statement:
  $services.query.xwql('xwqlstatement').execute()
• Return only 5 results at most:
  $services.query.xwql('xwqlstatement').setLimit(5).execute()
• Set the starting offset (starts at result number 5 and beyond):
  $services.query.xwql('xwqlstatement').setOffset(5).execute()
• Set the wiki on which to run the query (requires Programming Rights before XWiki 4.1):
  $services.query.xwql('xwqlstatement').setWiki('mywiki').execute()
• You can add filters to apply to the query and multiple filters can be added to a query.
  • The hidden filter will exclude documents marked as hidden from the query results, except if the user has chosen to see hidden documents in his profile preferences:
    $services.query.xwql('xwqlstatement').addFilter('hidden').execute()
  • The unique filter will make sure you don't get duplicate results with a short-form query:
    $services.query.xwql('xwqlstatement').addFilter('unique').execute()
  • The count filter allows to transform a short-form query into a count of the distinct results it would return. Unfortunately this doesn't work with XWQL on versions older than 4.4.1 and also it will return -1 if doc.fullname column is not selected:
    $services.query.xwql('xwqlstatement').addFilter('count').execute()
    ## You can also use the following shortcut
    $services.query.xwql('xwqlstatement').count()
  • The language filter will transform the query to also return document languages (the result you'll get is List<Object[]> with Object[0] being the document name and Object[1] being the document language, e.g. en, fr, fr_FR, etc): New in 5.1
    $services.query.xwql('xwqlstatement').addFilter('language').execute()
  • The currentlanguage filter will only return documents in the current language: New in 5.1
    $services.query.xwql('xwqlstatement').addFilter('currentlanguage').execute()
• Binding a LIKE value New in 8.4.5, 9.3RC1:

  You need to be careful about 2 things:

  • Define which part of the parameter you wish to escape. For example if you have a parameter representing a Document reference and you wish to find all children, you'll want to escape the % and _ characters (and even the [ character since on some DB the constructs [specifier] and [^specifier] have a special meaning) from the Document reference but end the parameter value with a % that you don't want to escape.
  • If you wish that your query works on MySQL then you need to be careful to also have the \ character escaped since MySQL considers it as its escape character by default.

  Thus the recommended approach is to do the following:

  $services.query.xwql('xwqlstatement like :ref').bindValue('ref').literal("${documentReference}.").anyChars().query().execute()

  The full API is:

  • literal(): Represents characters on which to perform escaping.
  • anyChar(): Represents the _ character in SQL (i.e. any single character).
  • anyChars(): Represents the % character in SQL (i.e. one or several characters).

  If you wish to bind several parameters at once you should write something like:

  #set ($queryParams = [])
  ...
  #set ($discard = $queryParams.add($services.query.parameter().literal($request.space)))
  ...
  $query.bindValues($queryParams)...
• Bind a non-LIKE value:
  $services.query.xwql('xwqlstatement containing :var').bindValue('var', 'value').execute()

  Specific example that will return all documents that have comments containing the test string:

  $services.query.xwql('select doc.fullName from Document doc, doc.object(XWiki.XWikiComments) com WHERE doc.translation = 0 and com.comment LIKE :value').bindValue('value', '%test%').execute()

  You can also bind a list or an array to a query parameter: New in 6.0

  #set ($query = $services.query.xwql('where doc.name in (:myList)'))
  $query.bindValue('myList', ['Activity', 'BlogPostClass', 'Welcome']).execute()
• Behaviors can be chained:
  $services.query.xwql('xwqlstatement').setWiki('mywiki').setOffset(2).setLimit(5).execute()

For HQL:

From other Scripting languages

For XWQL (example with Groovy):

For HQL:

From Java components

Get a QueryManager injected. For example :

Obtain and execute a query :

Example:

Pitfalls

Querying multiple wikis at once

When using the HQL or XWQL languages you can only query one wiki at a time (using the setWiki() call to set the wiki to query on, see above). The reason is that this does some database query on one schema (we cannot do queries on multiples database schema at once).

However, there's a solution, which is to use the SOLR language, which does queries against a SOLR index and thus on all subwikis.

See the Solr Query Langage documentation for details.

Finding pages under nested pages

You may be tempted to write:

However this will fail under MySQL (it'll work under HSQLDB though)! The reason is that MySQL considers the \ character as an escape character.

To make this query work on all DBs you need to write:

Note that % and _ are special LIKE characters (means any characters for the former and one character for the latter).

Since XWiki version 8.4.5 or 9.3RC1 you can simplify this to:

XWQL Implementation Details

The XWQL grammar is defined here.

Note that currently the XWQL implementation translates queries into HQL which are then executed using Hibernate against the RDBMS.

XWiki-specific extensions in XWQL over JPQL

• Short form queries:
  • where <expr> means select doc.fullName where <expr>
  • from <fromlist> [where <expr>] means select doc.fullName from Document as doc, <fromlist> [where <expr>]
• Special syntax for XWiki objects in from and where clauses:
  • from doc.object(Class) as obj
  • where doc.object(Class).prop = 'something'

  The class name must be quoted if it contains special characters (e.g. Unicode). Both single and double quotes can be used.

Note that any JPQL query is a correct XWQL query. This also means almost any HQL query (HQL is a JPQL superset) will work with XWQL (when executed on the XWiki Hibernate store).

Noteworthy differences between XWQL and HQL

Allowed HQL/XWQL select queries

Queries go through a validator to check if they are safe to be executed by anyone or restricted to user with progrmaming right.
You need to have programming right to use fully qualified select queries (if you don't specify the select part, select doc.fullname from Document doc is concatenated to the passed query) unless you use only the following columns:

In the standard Validator, the criteria to consider a query safe is if it's only selecting the following columns:

Customize allowed/unallowed queries

Using the XWiki object (Deprecated)

See the Velocity HQL Guide (till we incorporate it back in this guide).

For Developers

Query Filters

It's possible to write code to filter queries. By filtering, we mean the ability to perform modifications on the query statement, parameters and even the returned results from the store.

To write a query filter, create a Component implementing the QueryFilter interface role.

For example:

New in XWiki 9.3RC1 The filterQuery() method now allows to completely configure any part of the Query and since it's more generic it can be used as a replacement for the filterStatement() method.

Here's an example of how to use it to modify the statement passed: