<refentry id="glib-Relations-and-Tuples">
<refmeta>
<refentrytitle>Relations and Tuples</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>GLIB Library</refmiscinfo>
</refmeta>
<refnamediv>
<refname>Relations and Tuples</refname><refpurpose>tables of data which can be indexed on any number of fields.</refpurpose>
</refnamediv>
<refsynopsisdiv><title>Synopsis</title>
<synopsis>
#include <glib.h>
struct <link linkend="GRelation">GRelation</link>;
<link linkend="GRelation">GRelation</link>* <link linkend="g-relation-new">g_relation_new</link> (<link linkend="gint">gint</link> fields);
<link linkend="void">void</link> <link linkend="g-relation-index">g_relation_index</link> (<link linkend="GRelation">GRelation</link> *relation,
<link linkend="gint">gint</link> field,
<link linkend="GHashFunc">GHashFunc</link> hash_func,
<link linkend="GEqualFunc">GEqualFunc</link> key_equal_func);
<link linkend="void">void</link> <link linkend="g-relation-insert">g_relation_insert</link> (<link linkend="GRelation">GRelation</link> *relation,
...);
<link linkend="gboolean">gboolean</link> <link linkend="g-relation-exists">g_relation_exists</link> (<link linkend="GRelation">GRelation</link> *relation,
...);
<link linkend="gint">gint</link> <link linkend="g-relation-count">g_relation_count</link> (<link linkend="GRelation">GRelation</link> *relation,
<link linkend="gconstpointer">gconstpointer</link> key,
<link linkend="gint">gint</link> field);
<link linkend="GTuples">GTuples</link>* <link linkend="g-relation-select">g_relation_select</link> (<link linkend="GRelation">GRelation</link> *relation,
<link linkend="gconstpointer">gconstpointer</link> key,
<link linkend="gint">gint</link> field);
<link linkend="gint">gint</link> <link linkend="g-relation-delete">g_relation_delete</link> (<link linkend="GRelation">GRelation</link> *relation,
<link linkend="gconstpointer">gconstpointer</link> key,
<link linkend="gint">gint</link> field);
<link linkend="void">void</link> <link linkend="g-relation-destroy">g_relation_destroy</link> (<link linkend="GRelation">GRelation</link> *relation);
<link linkend="void">void</link> <link linkend="g-relation-print">g_relation_print</link> (<link linkend="GRelation">GRelation</link> *relation);
struct <link linkend="GTuples">GTuples</link>;
<link linkend="void">void</link> <link linkend="g-tuples-destroy">g_tuples_destroy</link> (<link linkend="GTuples">GTuples</link> *tuples);
<link linkend="gpointer">gpointer</link> <link linkend="g-tuples-index">g_tuples_index</link> (<link linkend="GTuples">GTuples</link> *tuples,
<link linkend="gint">gint</link> index_,
<link linkend="gint">gint</link> field);
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
A <link linkend="GRelation"><type>GRelation</type></link> is a table of data which can be indexed on any number of fields,
rather like simple database tables. A <link linkend="GRelation"><type>GRelation</type></link> contains a number of
records, called tuples. Each record contains a number of fields.
Records are not ordered, so it is not possible to find the record at a
particular index.
</para>
<para>
Note that <link linkend="GRelation"><type>GRelation</type></link> tables are currently limited to 2 fields.
</para>
<para>
To create a GRelation, use <link linkend="g-relation-new"><function>g_relation_new()</function></link>.
</para>
<para>
To specify which fields should be indexed, use <link linkend="g-relation-index"><function>g_relation_index()</function></link>.
Note that this must be called before any tuples are added to the <link linkend="GRelation"><type>GRelation</type></link>.
</para>
<para>
To add records to a <link linkend="GRelation"><type>GRelation</type></link> use <link linkend="g-relation-insert"><function>g_relation_insert()</function></link>.
</para>
<para>
To determine if a given record appears in a <link linkend="GRelation"><type>GRelation</type></link>, use
<link linkend="g-relation-exists"><function>g_relation_exists()</function></link>. Note that fields are compared directly, so pointers
must point to the exact same position (i.e. different copies of the same
string will not match.)
</para>
<para>
To count the number of records which have a particular value in a given
field, use <link linkend="g-relation-count"><function>g_relation_count()</function></link>.
</para>
<para>
To get all the records which have a particular value in a given field,
use <link linkend="g-relation-select"><function>g_relation_select()</function></link>. To access fields of the resulting records,
use <link linkend="g-tuples-index"><function>g_tuples_index()</function></link>. To free the resulting records use <link linkend="g-tuples-destroy"><function>g_tuples_destroy()</function></link>.
</para>
<para>
To delete all records which have a particular value in a given field,
use <link linkend="g-relation-delete"><function>g_relation_delete()</function></link>.
</para>
<para>
To destroy the <link linkend="GRelation"><type>GRelation</type></link>, use <link linkend="g-relation-destroy"><function>g_relation_destroy()</function></link>.
</para>
<para>
To help debug <link linkend="GRelation"><type>GRelation</type></link> objects, use <link linkend="g-relation-print"><function>g_relation_print()</function></link>.
</para>
</refsect1>
<refsect1>
<title>Details</title>
<refsect2>
<title><anchor id="GRelation"/>struct GRelation</title>
<indexterm><primary>GRelation</primary></indexterm><programlisting>struct GRelation;</programlisting>
<para>
The <link linkend="GRelation"><type>GRelation</type></link> struct is an opaque data structure to represent a
<link linkend="glib-Relations-and-Tuples">Relation</link>.
It should only be accessed via the following functions.
</para></refsect2>
<refsect2>
<title><anchor id="g-relation-new"/>g_relation_new ()</title>
<indexterm><primary>g_relation_new</primary></indexterm><programlisting><link linkend="GRelation">GRelation</link>* g_relation_new (<link linkend="gint">gint</link> fields);</programlisting>
<para>
Creates a new <link linkend="GRelation"><type>GRelation</type></link> with the given number of fields.
Note that currently the number of fields must be 2.
</para><variablelist role="params">
<varlistentry><term><parameter>fields</parameter> :</term>
<listitem><simpara>the number of fields.
</simpara></listitem></varlistentry>
<varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara>a new <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-relation-index"/>g_relation_index ()</title>
<indexterm><primary>g_relation_index</primary></indexterm><programlisting><link linkend="void">void</link> g_relation_index (<link linkend="GRelation">GRelation</link> *relation,
<link linkend="gint">gint</link> field,
<link linkend="GHashFunc">GHashFunc</link> hash_func,
<link linkend="GEqualFunc">GEqualFunc</link> key_equal_func);</programlisting>
<para>
Creates an index on the given field.
Note that this must be called before any records are added to the <link linkend="GRelation"><type>GRelation</type></link>.
</para><variablelist role="params">
<varlistentry><term><parameter>relation</parameter> :</term>
<listitem><simpara>a <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>field</parameter> :</term>
<listitem><simpara>the field to index, counting from 0.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>hash_func</parameter> :</term>
<listitem><simpara>a function to produce a hash value from the field data.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>key_equal_func</parameter> :</term>
<listitem><simpara>a function to compare two values of the given field.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-relation-insert"/>g_relation_insert ()</title>
<indexterm><primary>g_relation_insert</primary></indexterm><programlisting><link linkend="void">void</link> g_relation_insert (<link linkend="GRelation">GRelation</link> *relation,
...);</programlisting>
<para>
Inserts a record into a <link linkend="GRelation"><type>GRelation</type></link>.
</para><variablelist role="params">
<varlistentry><term><parameter>relation</parameter> :</term>
<listitem><simpara>a <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>...</parameter> :</term>
<listitem><simpara>the fields of the record to add. This must match the number of
fields in the <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-relation-exists"/>g_relation_exists ()</title>
<indexterm><primary>g_relation_exists</primary></indexterm><programlisting><link linkend="gboolean">gboolean</link> g_relation_exists (<link linkend="GRelation">GRelation</link> *relation,
...);</programlisting>
<para>
Returns <literal>TRUE</literal> if a record with the given values exists in a <link linkend="GRelation"><type>GRelation</type></link>.
Note that the values are compared directly, so that, for example, two
copies of the same string will not match.
</para><variablelist role="params">
<varlistentry><term><parameter>relation</parameter> :</term>
<listitem><simpara>a <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>...</parameter> :</term>
<listitem><simpara>the fields of the record to compare. The number must match the
number of fields in the <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
<varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara><literal>TRUE</literal> if a record matches.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-relation-count"/>g_relation_count ()</title>
<indexterm><primary>g_relation_count</primary></indexterm><programlisting><link linkend="gint">gint</link> g_relation_count (<link linkend="GRelation">GRelation</link> *relation,
<link linkend="gconstpointer">gconstpointer</link> key,
<link linkend="gint">gint</link> field);</programlisting>
<para>
Returns the number of tuples in a <link linkend="GRelation"><type>GRelation</type></link> that have the given value
in the given field.
</para><variablelist role="params">
<varlistentry><term><parameter>relation</parameter> :</term>
<listitem><simpara>a <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>key</parameter> :</term>
<listitem><simpara>the value to compare with.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>field</parameter> :</term>
<listitem><simpara>the field of each record to match.
</simpara></listitem></varlistentry>
<varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara>the number of matches.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-relation-select"/>g_relation_select ()</title>
<indexterm><primary>g_relation_select</primary></indexterm><programlisting><link linkend="GTuples">GTuples</link>* g_relation_select (<link linkend="GRelation">GRelation</link> *relation,
<link linkend="gconstpointer">gconstpointer</link> key,
<link linkend="gint">gint</link> field);</programlisting>
<para>
Returns all of the tuples which have the given key in the given field.
Use <link linkend="g-tuples-index"><function>g_tuples_index()</function></link> to access the returned records.
The returned records should be freed with <link linkend="g-tuples-destroy"><function>g_tuples_destroy()</function></link>.
</para><variablelist role="params">
<varlistentry><term><parameter>relation</parameter> :</term>
<listitem><simpara>a <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>key</parameter> :</term>
<listitem><simpara>the value to compare with.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>field</parameter> :</term>
<listitem><simpara>the field of each record to match.
</simpara></listitem></varlistentry>
<varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara>the records (tuples) that matched.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-relation-delete"/>g_relation_delete ()</title>
<indexterm><primary>g_relation_delete</primary></indexterm><programlisting><link linkend="gint">gint</link> g_relation_delete (<link linkend="GRelation">GRelation</link> *relation,
<link linkend="gconstpointer">gconstpointer</link> key,
<link linkend="gint">gint</link> field);</programlisting>
<para>
Deletes any records from a <link linkend="GRelation"><type>GRelation</type></link> that have the given key value in
the given field.
</para><variablelist role="params">
<varlistentry><term><parameter>relation</parameter> :</term>
<listitem><simpara>a <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>key</parameter> :</term>
<listitem><simpara>the value to compare with.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>field</parameter> :</term>
<listitem><simpara>the field of each record to match.
</simpara></listitem></varlistentry>
<varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara>the number of records deleted.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-relation-destroy"/>g_relation_destroy ()</title>
<indexterm><primary>g_relation_destroy</primary></indexterm><programlisting><link linkend="void">void</link> g_relation_destroy (<link linkend="GRelation">GRelation</link> *relation);</programlisting>
<para>
Destroys the <link linkend="GRelation"><type>GRelation</type></link>, freeing all memory allocated.
However, it does not free memory allocated for the
tuple data, so you should free that first if appropriate.
</para><variablelist role="params">
<varlistentry><term><parameter>relation</parameter> :</term>
<listitem><simpara>a <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-relation-print"/>g_relation_print ()</title>
<indexterm><primary>g_relation_print</primary></indexterm><programlisting><link linkend="void">void</link> g_relation_print (<link linkend="GRelation">GRelation</link> *relation);</programlisting>
<para>
Outputs information about all records in a <link linkend="GRelation"><type>GRelation</type></link>, as well as the indexes.
It is for debugging.
</para><variablelist role="params">
<varlistentry><term><parameter>relation</parameter> :</term>
<listitem><simpara>a <link linkend="GRelation"><type>GRelation</type></link>.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="GTuples"/>struct GTuples</title>
<indexterm><primary>GTuples</primary></indexterm><programlisting>struct GTuples {
guint len;
};
</programlisting>
<para>
The <link linkend="GTuples"><type>GTuples</type></link> struct is used to return records (or tuples) from the
<link linkend="GRelation"><type>GRelation</type></link> by <link linkend="g-relation-select"><function>g_relation_select()</function></link>.
It only contains one public member - the number of records that matched.
To access the matched records, you must use <link linkend="g-tuples-index"><function>g_tuples_index()</function></link>.
</para><variablelist role="struct">
<varlistentry>
<term><link linkend="guint">guint</link> <structfield>len</structfield></term>
<listitem><simpara>the number of records that matched.
</simpara></listitem>
</varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-tuples-destroy"/>g_tuples_destroy ()</title>
<indexterm><primary>g_tuples_destroy</primary></indexterm><programlisting><link linkend="void">void</link> g_tuples_destroy (<link linkend="GTuples">GTuples</link> *tuples);</programlisting>
<para>
Frees the records which were returned by <link linkend="g-relation-select"><function>g_relation_select()</function></link>.
This should always be called after <link linkend="g-relation-select"><function>g_relation_select()</function></link> when you are
finished with the records.
The records are not removed from the <link linkend="GRelation"><type>GRelation</type></link>.
</para><variablelist role="params">
<varlistentry><term><parameter>tuples</parameter> :</term>
<listitem><simpara>the tuple data to free.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="g-tuples-index"/>g_tuples_index ()</title>
<indexterm><primary>g_tuples_index</primary></indexterm><programlisting><link linkend="gpointer">gpointer</link> g_tuples_index (<link linkend="GTuples">GTuples</link> *tuples,
<link linkend="gint">gint</link> index_,
<link linkend="gint">gint</link> field);</programlisting>
<para>
Gets a field from the records returned by <link linkend="g-relation-select"><function>g_relation_select()</function></link>.
It returns the given field of the record at the given index.
The returned value should not be changed.
</para><variablelist role="params">
<varlistentry><term><parameter>tuples</parameter> :</term>
<listitem><simpara>the tuple data, returned by <link linkend="g-relation-select"><function>g_relation_select()</function></link>.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>index_</parameter> :</term>
<listitem><simpara>the index of the record.
</simpara></listitem></varlistentry>
<varlistentry><term><parameter>field</parameter> :</term>
<listitem><simpara>the field to return.
</simpara></listitem></varlistentry>
<varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara>the field of the record.
</simpara></listitem></varlistentry>
</variablelist></refsect2>
</refsect1>
</refentry>