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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id-1.5.4.7"></a>Schema conversion</h2></div></div></div>
<p>
If you are porting your application from GConf, most likely you already
have a GConf schema. GConf comes with a commandline tool
gsettings-schema-convert that can help with the task of converting
a GConf schema into an equivalent GSettings schema. The tool is not
perfect and may need assistence in some cases.
</p>
<div class="example">
<a name="id-1.5.4.7.3"></a><p class="title"><b>Example 1. An example for using gsettings-schema-convert</b></p>
<div class="example-contents">
<p>Running <strong class="userinput"><code>gsettings-schema-convert --gconf --xml --schema-id "org.gnome.font-rendering" --output org.gnome.font-rendering.gschema.xml destop_gnome_font_rendering.schemas</code></strong> on the following <code class="filename">desktop_gnome_font_rendering.schemas</code> file:
</p>
<pre class="programlisting">
<?xml version="1.0"?>
<gconfschemafile>
<schemalist>
<schema>
<key>/schemas/desktop/gnome/font_rendering/dpi</key>
<applyto>/desktop/gnome/font_rendering/dpi</applyto>
<owner>gnome</owner>
<type>int</type>
<default>96</default>
<locale name="C">
<short>DPI</short>
<long>The resolution used for converting font sizes to pixel sizes, in dots per inch.</long>
</locale>
</schema>
</schemalist>
</gconfschemafile>
</pre>
<p>
produces a <code class="filename">org.gnome.font-rendering.gschema.xml</code> file with the following content:
</p>
<pre class="programlisting">
<schemalist>
<schema id="org.gnome.font-rendering" path="/desktop/gnome/font_rendering/">
<key name="dpi" type="i">
<default>96</default>
<summary>DPI</summary>
<description>The resolution used for converting font sizes to pixel sizes, in dots per inch.</description>
</key>
</schema>
</schemalist>
</pre>
<p>
</p>
</div>
</div>
<br class="example-break"><p>
GSettings schemas are identified at runtime by their id (as specified
in the XML source file). It is recommended to use a dotted name as schema
id, similar in style to a D-Bus bus name, e.g. "org.gnome.SessionManager".
In cases where the settings are general and not specific to one application,
the id should not use StudlyCaps, e.g. "org.gnome.font-rendering".
The filename used for the XML schema source is immaterial, but
schema compiler expects the files to have the extension
<code class="filename">.gschema.xml</code>. It is recommended to simply
use the schema id as the filename, followed by this extension,
e.g. <code class="filename">org.gnome.SessionManager.gschema.xml</code>.
</p>
<p>
The XML source file for your GSettings schema needs to get installed
into <code class="filename">$datadir/glib-2.0/schemas</code>, and needs to be
compiled into a binary form. At runtime, GSettings looks for compiled
schemas in the <code class="filename">glib-2.0/schemas</code> subdirectories
of all <code class="envar">XDG_DATA_DIRS</code> directories, so if you install
your schema in a different location, you need to set the
<code class="envar">XDG_DATA_DIRS</code> environment variable appropriately.
</p>
<p>
Schemas are compiled into binary form by the
glib-compile-schemas utility.
GIO provides a <code class="literal">glib_compile_schemas</code>
variable for the schema compiler.
</p>
<p>
You can ignore all of this by using the provided m4 macros. To
do this, add to your <code class="filename">configure.ac</code>:
</p>
<pre class="programlisting">
GLIB_GSETTINGS
</pre>
<p>
The corresponding <code class="filename">Makefile.am</code> fragment looks like
this:
</p>
<pre class="programlisting">
# gsettings_SCHEMAS is a list of all the schemas you want to install
gsettings_SCHEMAS = my.app.gschema.xml
# include the appropriate makefile rules for schema handling
@GSETTINGS_RULES@
</pre>
<p>
</p>
<p>
This is not sufficient on its own. You need to mention what the source
of the <code class="filename">my.app.gschema.xml</code> file is. If the schema
file is distributed directly with your project's tarball then a mention
in <code class="varname">EXTRA_DIST</code> is appropriate. If the schema file is
generated from another source then you will need the appropriate rule
for that, plus probably an item in <code class="varname">EXTRA_DIST</code> for the
source files used by that rule.
</p>
<p>
One possible pitfall in doing schema conversion is that the default
values in GSettings schemas are parsed by the <a href="../glib-GVariant.html#GVariant"><span class="type">GVariant</span></a> parser.
This means that strings need to include quotes in the XML. Also note
that the types are now specified as <a href="../glib-GVariant.html#GVariant"><span class="type">GVariant</span></a> type strings.
</p>
<pre class="programlisting">
<type>string</type>
<default>rgb</default>
</pre>
<p>
becomes
</p>
<pre class="programlisting">
<key name="rgba-order" type="s">
<default>'rgb'</default> <!-- note quotes -->
</key>
</pre>
<p>
</p>
<p>
Another possible complication is that GConf specifies full paths
for each key, while a GSettings schema has a 'path' attribute that
contains the prefix for all the keys in the schema, and individual
keys just have a simple name. So
</p>
<pre class="programlisting">
<key>/schemas/desktop/gnome/font_rendering/antialiasing</key>
</pre>
<p>
becomes
</p>
<pre class="programlisting">
<schema id="org.gnome.font" path="/desktop/gnome/font_rendering/">
<key name="antialiasing" type="s">
</pre>
<p>
</p>
<p>
Default values can be localized in both GConf and GSettings schemas,
but GSettings uses gettext for the localization. You can specify
the gettext domain to use in the <code class="sgmltag-attribute">gettext-domain</code>
attribute. Therefore, when converting localized defaults in GConf,
</p>
<pre class="programlisting">
<key>/schemas/apps/my_app/font_size</key>
<locale name="C">
<default>18</default>
</locale>
<locale name="be">
<default>24</default>
</locale>
</key>
</pre>
<p>
becomes
</p>
<pre class="programlisting">
<schema id="..." gettext-domain="your-domain">
...
<key name="font-size" type="i">
<default l10n="messages" context="font_size">18</default>
</key>
</pre>
<p>
</p>
<p>
GSettings uses gettext for translation of default values.
The string that is translated is exactly the string that appears
inside of the <code class="sgmltag-starttag"><default></code> element. This
includes the quotation marks that appear around strings.
Default values must be marked with the <code class="varname">l10n</code>
attribute in the <code class="sgmltag-starttag"><default></code> tag, which
should be set as equal to <code class="literal">'messages'</code> or
<code class="literal">'time'</code> depending on the desired category. An
optional translation context can also be specified with the
<code class="varname">context</code> attribute, as in the example. This
is usually recommended, since the string "<code class="literal">18</code>"
is not particularly easy to translate without context. The
translated version of the default value should be stored in the
specified <code class="varname">gettext-domain</code>. Care must be taken
during translation to ensure that all translated values remain
syntactically valid; mistakes here will cause runtime errors.
</p>
<p>
GSettings schemas have optional <code class="sgmltag-starttag"><summary></code> and
<code class="sgmltag-starttag"><description></code> elements for each key which
correspond to the <code class="sgmltag-starttag"><short></code> and
<code class="sgmltag-starttag"><long></code> elements in the GConf schema and
will be used in similar ways by a future gsettings-editor, so you
should use the same conventions for them: The summary is just a short
label with no punctuation, the description can be one or more complete
sentences. If multiple paragraphs are desired for the description, the
paragraphs should be separated by a completely empty line.
</p>
<p>
Translations for these strings will also be handled
via gettext, so you should arrange for these strings to be
extracted into your gettext catalog. One way to do that is to use
intltool. Since intltool 0.50.1, schema files are
supported, so all you have to do is to add your .gschema.xml
files to <code class="filename">POTFILES.in</code> with a line like
</p>
<pre class="programlisting">
[type: gettext/gsettings]data/org.foo.MyApp.gschema.xml
</pre>
<p>
</p>
<p>
GSettings is a bit more restrictive about key names than GConf. Key
names in GSettings can be at most 32 characters long, and must only
consist of lowercase characters, numbers and dashes, with no
consecutive dashes. The first character must not be a number or dash,
and the last character cannot be '-'.
</p>
<p>
If you are using the GConf backend for GSettings during the
transition, you may want to keep your key names the same they
were in GConf, so that existing settings in the users GConf
database are preserved. You can achieve this by using the
<code class="option">--allow-any-name</code> with the
glib-compile-schemas schema
compiler. Note that this option is only meant
to ease the process of porting your application, allowing parts
of your application to continue to access GConf and parts to use
GSettings. By the time you have finished porting your application
you must ensure that all key names are valid.
</p>
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