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<a href="#pub-types">Public Types</a> |
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<div class="title">Wt::Dbo::dbo_traits< C > Class Template Reference<div class="ingroups"><a class="el" href="group__dbo.html">Database Objects (Wt::Dbo)</a></div></div> </div>
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<!-- doxytag: class="Wt::Dbo::dbo_traits" --><!-- doxytag: inherits="Wt::Dbo::dbo_default_traits" -->
<p>Traits for a class mapped with Wt::Dbo.
<a href="structWt_1_1Dbo_1_1dbo__traits.html#details">More...</a></p>
<p><code>#include <Wt/Dbo/Dbo></code></p>
<div class="dynheader">
Inheritance diagram for Wt::Dbo::dbo_traits< C >:</div>
<div class="dyncontent">
<div class="center"><img src="structWt_1_1Dbo_1_1dbo__traits__inherit__graph.png" border="0" usemap="#Wt_1_1Dbo_1_1dbo__traits_3_01C_01_4_inherit__map" alt="Inheritance graph"/></div>
<map name="Wt_1_1Dbo_1_1dbo__traits_3_01C_01_4_inherit__map" id="Wt_1_1Dbo_1_1dbo__traits_3_01C_01_4_inherit__map">
<area shape="rect" href="structWt_1_1Dbo_1_1dbo__default__traits.html" title="Default traits for a class mapped with Wt::Dbo." alt="" coords="5,5,184,32"/></map>
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<p><a href="classWt_1_1Dbo_1_1dbo__traits-members.html">List of all members.</a></p>
<table class="memberdecls">
<tr><td colspan="2"><h2><a name="pub-types"></a>
Public Types</h2></td></tr>
<tr><td class="memItemLeft" align="right" valign="top">typedef YourIdType </td><td class="memItemRight" valign="bottom"><a class="el" href="structWt_1_1Dbo_1_1dbo__traits.html#afb62c3f28967b0b14b13360d47cd37dc">IdType</a></td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Type of the primary key. <a href="#afb62c3f28967b0b14b13360d47cd37dc"></a><br/></td></tr>
<tr><td colspan="2"><h2><a name="pub-static-methods"></a>
Static Public Member Functions</h2></td></tr>
<tr><td class="memItemLeft" align="right" valign="top">static <a class="el" href="structWt_1_1Dbo_1_1dbo__default__traits.html#a89170e677a75348ef6913d9f4ba496ae">IdType</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="structWt_1_1Dbo_1_1dbo__traits.html#aae2a13a4ca038f5bad337fbc2d70d37c">invalidId</a> ()</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Returns the sentinel value for a <code>null</code> id. <a href="#aae2a13a4ca038f5bad337fbc2d70d37c"></a><br/></td></tr>
<tr><td class="memItemLeft" align="right" valign="top">static const char * </td><td class="memItemRight" valign="bottom"><a class="el" href="structWt_1_1Dbo_1_1dbo__traits.html#a44c5455df89390fae082aadf7cf1bc13">surrogateIdField</a> ()</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Configures the surrogate primary key field. <a href="#a44c5455df89390fae082aadf7cf1bc13"></a><br/></td></tr>
<tr><td class="memItemLeft" align="right" valign="top">static const char * </td><td class="memItemRight" valign="bottom"><a class="el" href="structWt_1_1Dbo_1_1dbo__traits.html#a701b53b0401836a7c966c619f3c9656d">versionField</a> ()</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Configures the optimistic concurrency version field. <a href="#a701b53b0401836a7c966c619f3c9656d"></a><br/></td></tr>
</table>
<hr/><a name="details" id="details"></a><h2>Detailed Description</h2>
<div class="textblock"><h3>template<class C><br/>
class Wt::Dbo::dbo_traits< C ></h3>
<p>Traits for a class mapped with Wt::Dbo. </p>
<p>The traits class provides some of the mapping properties related to the primary key and optimistic concurrency locking using a version field.</p>
<p>See <a class="el" href="structWt_1_1Dbo_1_1dbo__default__traits.html" title="Default traits for a class mapped with Wt::Dbo.">dbo_default_traits</a> for default values.</p>
<p>The following example changes the surrogate id field name for a class <code>Foo</code> from the default <code>"id"</code> to <code>"foo_id"</code>:</p>
<div class="fragment"><pre class="fragment"> <span class="keyword">namespace </span>Wt {
<span class="keyword">namespace </span>Dbo {
<span class="keyword">template</span><>
<span class="keyword">struct </span>dbo_traits<Foo>
{
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keywordtype">char</span> *<a class="code" href="structWt_1_1Dbo_1_1dbo__traits.html#a44c5455df89390fae082aadf7cf1bc13" title="Configures the surrogate primary key field.">surrogateIdField</a>() { <span class="keywordflow">return</span> <span class="stringliteral">"foo_id"</span>; }
};
}
}
</pre></div> </div><hr/><h2>Member Typedef Documentation</h2>
<a class="anchor" id="afb62c3f28967b0b14b13360d47cd37dc"></a><!-- doxytag: member="Wt::Dbo::dbo_traits::IdType" ref="afb62c3f28967b0b14b13360d47cd37dc" args="" -->
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<td class="memname">typedef YourIdType <a class="el" href="structWt_1_1Dbo_1_1dbo__traits.html">Wt::Dbo::dbo_traits</a>< C >::<a class="el" href="structWt_1_1Dbo_1_1dbo__default__traits.html#a89170e677a75348ef6913d9f4ba496ae">IdType</a></td>
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<p>Type of the primary key. </p>
<p>This indicates the type of the primary key, which needs to be <code>long long</code> for a surrogate id, but can be any type supported by <a class="el" href="group__dbo.html#ga864a2e134149e7f614f45967777992c7" title="Maps a database object field.">Wt::Dbo::field()</a> (including composite types) for a natural primary key.</p>
<p>The following operations need to be supported for an id value:</p>
<ul>
<li><em>default constructor</em></li>
<li><em>copy constructor</em></li>
<li>serialization to a string (for formatting an error message in exceptions) : <code>std::ostream << id</code></li>
<li>comparison operator (for use as a key in a std::map): <code>id == id</code></li>
<li>less than operator (for use as a key in a std::map): <code>id < id</code></li>
</ul>
<p>Only the default <code>long long</code> is supported for an auto-incrementing surrogate primary key. You need to change the default key type typically in conjuction with specifying a natural id, see <a class="el" href="group__dbo.html#ga42c50bd3bfc38ad8c810b30b279b0ba6" title="Maps a natural primary key (id) field.">Wt::Dbo::id()</a>.</p>
<p>The following example illustrates how to prepare a type to be usable as a composite id type:</p>
<div class="fragment"><pre class="fragment"> <span class="keyword">struct </span>Coordinate {
<span class="keywordtype">int</span> x, y;
Coordinate()
: x(-1), y(-1) { }
<span class="keywordtype">bool</span> operator== (<span class="keyword">const</span> Coordinate& other)<span class="keyword"> const </span>{
<span class="keywordflow">return</span> x == other.x && y == other.y;
}
<span class="keywordtype">bool</span> operator< (<span class="keyword">const</span> Coordinate& other)<span class="keyword"> const </span>{
<span class="keywordflow">if</span> (x < other.x)
<span class="keywordflow">return</span> <span class="keyword">true</span>;
<span class="keywordflow">else</span> <span class="keywordflow">if</span> (x == other.x)
<span class="keywordflow">return</span> y < other.y;
<span class="keywordflow">else</span>
<span class="keywordflow">return</span> <span class="keyword">false</span>;
}
};
std::ostream& operator<< (std::ostream& o, <span class="keyword">const</span> Coordinate& c)
{
<span class="keywordflow">return</span> o << <span class="stringliteral">"("</span> << c.x << <span class="stringliteral">", "</span> << c.y << <span class="stringliteral">")"</span>;
}
<span class="keyword">namespace </span>Wt {
<span class="keyword">namespace </span>Dbo {
<span class="keyword">template</span> <<span class="keyword">class</span> Action>
<span class="keywordtype">void</span> <a class="code" href="group__dbo.html#ga864a2e134149e7f614f45967777992c7" title="Maps a database object field.">field</a>(Action& action, Coordinate& coordinate, <span class="keyword">const</span> std::string& name, <span class="keywordtype">int</span> size = -1)
{
<a class="code" href="group__dbo.html#ga864a2e134149e7f614f45967777992c7" title="Maps a database object field.">field</a>(action, coordinate.x, name + <span class="stringliteral">"_x"</span>);
<a class="code" href="group__dbo.html#ga864a2e134149e7f614f45967777992c7" title="Maps a database object field.">field</a>(action, coordinate.y, name + <span class="stringliteral">"_y"</span>);
}
}
}
</pre></div>
<p>Reimplemented from <a class="el" href="structWt_1_1Dbo_1_1dbo__default__traits.html#a89170e677a75348ef6913d9f4ba496ae">Wt::Dbo::dbo_default_traits</a>.</p>
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<hr/><h2>Member Function Documentation</h2>
<a class="anchor" id="aae2a13a4ca038f5bad337fbc2d70d37c"></a><!-- doxytag: member="Wt::Dbo::dbo_traits::invalidId" ref="aae2a13a4ca038f5bad337fbc2d70d37c" args="()" -->
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template<class C> </div>
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<td class="memname">static <a class="el" href="structWt_1_1Dbo_1_1dbo__default__traits.html#a89170e677a75348ef6913d9f4ba496ae">IdType</a> <a class="el" href="structWt_1_1Dbo_1_1dbo__traits.html">Wt::Dbo::dbo_traits</a>< C >::invalidId </td>
<td>(</td>
<td class="paramname"></td><td>)</td>
<td><code> [static]</code></td>
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<div class="memdoc">
<p>Returns the sentinel value for a <code>null</code> id. </p>
<p>When used as a foreign key, this value is used to represent a <code>null</code> value. </p>
<p>Reimplemented from <a class="el" href="structWt_1_1Dbo_1_1dbo__default__traits.html#a6bb01d0dc6a5bbd25481fa16b642b996">Wt::Dbo::dbo_default_traits</a>.</p>
</div>
</div>
<a class="anchor" id="a44c5455df89390fae082aadf7cf1bc13"></a><!-- doxytag: member="Wt::Dbo::dbo_traits::surrogateIdField" ref="a44c5455df89390fae082aadf7cf1bc13" args="()" -->
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<td class="memname">static const char* <a class="el" href="structWt_1_1Dbo_1_1dbo__traits.html">Wt::Dbo::dbo_traits</a>< C >::surrogateIdField </td>
<td>(</td>
<td class="paramname"></td><td>)</td>
<td><code> [static]</code></td>
</tr>
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<p>Configures the surrogate primary key field. </p>
<p>Returns the field name which is the surrogate primary key, corresponding to the object's id.</p>
<p>You can disable this auto-incrementing surrogate id by returning <code>0</code> instead. In that case you will need to define a natural id for your class using <a class="el" href="group__dbo.html#ga42c50bd3bfc38ad8c810b30b279b0ba6" title="Maps a natural primary key (id) field.">Wt::Dbo::id()</a>. </p>
<p>Reimplemented from <a class="el" href="structWt_1_1Dbo_1_1dbo__default__traits.html#a0c092c6b045f77d4fc04b5360b762b7f">Wt::Dbo::dbo_default_traits</a>.</p>
</div>
</div>
<a class="anchor" id="a701b53b0401836a7c966c619f3c9656d"></a><!-- doxytag: member="Wt::Dbo::dbo_traits::versionField" ref="a701b53b0401836a7c966c619f3c9656d" args="()" -->
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<td class="memname">static const char* <a class="el" href="structWt_1_1Dbo_1_1dbo__traits.html">Wt::Dbo::dbo_traits</a>< C >::versionField </td>
<td>(</td>
<td class="paramname"></td><td>)</td>
<td><code> [static]</code></td>
</tr>
</table>
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<div class="memdoc">
<p>Configures the optimistic concurrency version field. </p>
<p>Optimistic concurrency locking is used to detect concurrent updates by an object from multiple sessions. On each update, the version of a record is at the same time checked (to see if it matches the version of the record that was read), and incremented. A <a class="el" href="classWt_1_1Dbo_1_1StaleObjectException.html" title="Exception thrown when Wt::Dbo detects a concurrent modification">StaleObjectException</a> is thrown if a record was modified by another session since it was read.</p>
<p>This method must return the database field name used for this version field.</p>
<p>You can disable optimistic locking using a version field all together for your class by returning <code>0</code> instead. </p>
<p>Reimplemented from <a class="el" href="structWt_1_1Dbo_1_1dbo__default__traits.html#af4da1fde75771c5f2e707827e2a885c4">Wt::Dbo::dbo_default_traits</a>.</p>
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