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From Apache Wiki <wikidi...@apache.org>
Subject [Solr Wiki] Update of "CurrencyField" by JanHoydahl
Date Thu, 08 Mar 2012 23:11:01 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Solr Wiki" for change notification.

The "CurrencyField" page has been changed by JanHoydahl:
http://wiki.apache.org/solr/CurrencyField

Comment:
Updated to match latest patch

New page:
<!> Work in progress at [[https://issues.apache.org/jira/browse/SOLR-2202|SOLR-2202]]

The CurrencyField type was created by Greg Fodor in [[https://issues.apache.org/jira/browse/SOLR-2202|SOLR-2202]],
and is an advanced poly field type indexing a monetary value as both value and currency. It
lets e.g. an e-commerce site to display and query prices in many currencies, while only indexing
the price in one field/currency.

The field type is backed by an XML file {{{currency.xml}}} specifying exchange rates. This
file may be updated without need for reindexing, and a reload-core will set live the updated
exchange rates.

=== Configuration ===
See example schema for example of how to use the field type. The field type and field is defined
in schema.xml as follows:
{{{
  <fieldType name="currency" class="solr.CurrencyField" currencyConfig="currency.xml" />

  <dynamicField name="*_c" type="currency" defaultCurrency="EUR" />
}}}

!DefaultCurrency will be used if you do not specify a currency. The default defaultCurrency
is {{{USD}}}, if not specified. Note that defaultCurrency cannot be changed unless followed
by a full re-index.

You then need to point to a {{{currency.xml}}} file specifying the exchange rates:

{{{
<currencyConfig version="1.0">
  <rates>
    <!-- Example -->
    <rate from="USD" to="JPY" rate="81.29"/>

    <!-- Fake rates for testing -->
    <rate from="USD" to="EUR" rate="2.5"/>
    <rate from="USD" to="GBP" rate="0.5"/>
    <rate from="EUR" to="GBP" rate="0.5"/>

    <!-- Asymmetric rate -->
    <rate from="EUR" to="USD" rate="0.5"/>
  </rates>
</currencyConfig>
}}}

Note that you need a rate entry between every two pairs of currencies you will index or query.
So if you handle USD, EUR and GBP, you need USD->EUR, USD->GBP and EUR->GBP, so that
all possible conversions can be done. If you only index one currency (say USD) but want to
query or convert multiple, it is enough to have rates between USD and all currencies you'll
query or display.

By default the rate will be symmetrical, but you may override this by explicitly specifying
the reverse rate.

!CurrencyField supports replication, given that you explicitly configure replication for {{{currency.xml}}}.
Upon the arrival of a new version of currency.xml, Solr slaves will do a core reload and begin
using the new exchange rates. See [[SolrReplication#How_are_configuration_files_replicated.3F|SolrReplication]]
for more.

=== Indexing ===
When you index e.g. a price, you specify value and currency separated by comma:
{{{
<doc>
  <field name="id">1</field>
  <field name="price">1.00,USD</field>
</doc>
}}}

Here, 1.00,USD is assumed to mean $1.00. Note that regardless of the currency being indexed,
you must encode the value as a floating point value (with a decimal point.) The fractional
portion of the floating point value is interpreted based upon the currency, via Currency.getDefaultFractionDigits().


=== Querying ===
The !CurrencyField supports both point queries and range queries. Here are some valid money
queries. Assume default currency is {{{USD}}}.
In the example schema there is a copyField from "price" to "price_c", meaning that you can
test this on the example data:
{{{
price_c:25.00,USD                 or price_c:25.00               Both of these will query
for USD 25.00 since USD is default
price_c:[* TO 10.00,USD]          or price_c:[* TO 10.00]
price_c:[10.00,EUR TO 100.00,EUR]
price_c:10.00,NOK
}}}

=== Usage ===

Solr documents will always yield the currency values they were indexed with, regardless of
how they were queried for. For example, a set of documents indexed in USD will yield USD values
for its Currency fields regardless if you performed queries in EUR. 

So, for the display of Currency fields to a user, it is often necessary to perform a second
currency conversion once the documents are returned for display purposes. For accuracy, this
conversion should apply the same exchange rates in the currency.xml file available to Solr.
 
== TODO ==

 * facet.range is not yet supported for this field type - See [[https://issues.apache.org/jira/browse/SOLR-3218|SOLR-3218]]

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