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diff --git a/doc/manual.xhtml b/doc/manual.xhtml index 246f4af..e5c7419 100644 --- a/doc/manual.xhtml +++ b/doc/manual.xhtml @@ -2657,10 +2657,10 @@ transfer (database& db, <h2><a name="3.9">3.9 Deleting Persistent Objects</a></h2> <p>To delete a persistent object's state from the database we use the - <code>database::erase()</code> function template. If the application - still has an instance of the erased object, this instance becomes - transient. The <code>erase()</code> function has the following - overloaded versions:</p> + <code>database::erase()</code> or <code>database::erase_query()</code> + function templates. If the application still has an instance of the + erased object, this instance becomes transient. The <code>erase()</code> + function has the following overloaded versions:</p> <pre class="c++"> template <typename T> @@ -2709,6 +2709,43 @@ db.erase<person> (joe_id); t.commit (); </pre> + <p>The <code>erase_query()</code> function allows us to delete + the state of multiple objects matching certain criteria. It uses + the query expression of the <code>database::query()</code> function + (<a href="#4">Chapter 4, "Querying the Database"</a>) and, + because the ODB query facility is optional, it is only available + if the <code>--generate-query</code> ODB compiler option was + specified. The <code>erase_query()</code> function has the + following overloaded versions:</p> + + <pre class="c++"> + template <typename T> + unsigned long long + erase_query (); + + template <typename T> + unsigned long long + erase_query (const odb::query<T>&); + </pre> + + <p>The first <code>erase_query()</code> function is used to delete + the state of all the persistent objects of a given type stored + in the database. The second function uses the passed query instance + to only delete the state of objects matching the query criteria. + Both functions return the number of objects erased. When calling + the <code>erase_query()</code> function, we have to explicitly + specify the object type we are erasing. For example:</p> + + <pre class="c++"> +typedef odb::query<person> query; + +transaction t (db.begin ()); + +db.erase_query<person> (query::last == "Doe" && query::are < 30); + +t.commit (); + </pre> + <h2><a name="3.10">3.10 Executing Native SQL Statements</a></h2> <p>In some situations we may need to execute native SQL statements @@ -8926,7 +8963,8 @@ class person <p>If foreign key constraints checking is disabled or not available, then inconsistencies in object relationships will not be detected. - Furthermore, using the <code>erase_query()</code> function (@@ ref) + Furthermore, using the <code>erase_query()</code> function + (<a href="#3.9">Section 3.9, "Deleting Persistent Objects"</a>) to delete persistent objects that contain containers will not work correctly. Container data for such objects will not be deleted.</p> |