From 008087de38f21d6a2c160a93df1942215cf90df9 Mon Sep 17 00:00:00 2001
From: Martin Goik <goik@hdm-stuttgart.de>
Date: Fri, 22 Feb 2013 08:10:30 +0100
Subject: [PATCH] Criteria based queries
---
Doc/course.xml | 200 +++++++++++++++---
.../hibintro/v1/run/GetUsersAsAttributes.java | 48 +++++
.../v1/run/RetrieveAllByCriteria.java | 46 ++++
3 files changed, 267 insertions(+), 27 deletions(-)
create mode 100644 ws/eclipse/HibIntro/src/main/java/hibintro/v1/run/GetUsersAsAttributes.java
create mode 100644 ws/eclipse/HibIntro/src/main/java/hibintro/v1/run/RetrieveAllByCriteria.java
diff --git a/Doc/course.xml b/Doc/course.xml
index d84d3147b..4490bd155 100644
--- a/Doc/course.xml
+++ b/Doc/course.xml
@@ -15959,36 +15959,39 @@ import javax.persistence.Entity;
</figure>
</section>
- <section xml:id="loadingObjects">
- <title>Loading Objects</title>
+ <section xml:id="loadingObjectsByPrimaryKey">
+ <title>Loading Objects by primary key</title>
<para>Having persisted a single
<classname>hibintro.v1.model.User</classname> instance by means of
<classname>hibintro.v1.run.PersistSingleUser</classname> we may now
load the database object. The easiest way is based on both the
- requested object's type and its primary key value:</para>
+ requested object's type <coref linkend="specLoadType"/> and its
+ primary key value <coref linkend="specLoadPrimaryKey"/>:</para>
- <programlisting>package hibintro.v1.run;
+ <figure xml:id="loadByClassAndPrimaryKey">
+ <title>Loading a single object by a primary key value.</title>
+
+ <programlisting>package hibintro.v1.run;
...
public class RetrieveSingleUser {
-
- public static void main(String[] args) {
- final Session session = HibernateUtil.createSessionFactory("hibernate.cfg.xml").openSession();
-
+...
final Transaction transaction = session.beginTransaction();
- final User u = (User) session.load(User.class, "goik");
- if (null != u ) {
- System.out.println("Found user '" + u.getCname() + "'");
- } else {
+ final User u = (User) session.load(<emphasis role="bold">User.class</emphasis> <co
+ xml:id="specLoadType"/>, "<emphasis role="bold">goik</emphasis>" <co
+ xml:id="specLoadPrimaryKey"/>);
+ if (null == u ) {
System.out.println("No such user 'goik'");
+ } else {
+ System.out.println("Found user '" + u.getCname() + "'");
}
- transaction.commit();
- }
-}</programlisting>
+ transaction.commit();...</programlisting>
+ </figure>
- <para>This retrieves the expected result among logged SQL
- <quote>background</quote> statements:</para>
+ <para>This retrieves the expected result. Buried in other log
+ messages we find the following SQL <quote>background</quote>
+ statement:</para>
<programlisting>...
INFO: HHH000232: Schema update complete
@@ -16003,8 +16006,73 @@ Hibernate:
Found user 'Martin Goik'</programlisting>
- <para>Often we are interested in a (sub)set of results. We first
- populate our database with additional
+ <qandaset role="exercise">
+ <qandadiv>
+ <qandaentry>
+ <question>
+ <para>Actually the code in <xref
+ linkend="loadByClassAndPrimaryKey"/> is not quite correct.
+ Execute it with a non-existing primary key value i.e.
+ <quote>goik2</quote>. What do you observe? Can you explain
+ that behaviour?</para>
+
+ <para>Read the documentation of the
+ <classname>session.org.hibernate.Session</classname>.<code>load()</code>
+ method and correct the code snippet.</para>
+ </question>
+
+ <answer>
+ <para>If there is no corresponding database object we
+ receive a
+ <classname>org.hibernate.ObjectNotFoundException</classname>
+ :<coref linkend="loadUserObjectNotFoundException"/></para>
+
+ <programlisting>Hibernate:
+ select
+ user0_.uid as uid0_0_,
+ user0_.cname as cname0_0_
+ from
+ User user0_
+ where
+ user0_.uid=?
+Exception in thread "main" org.hibernate.ObjectNotFoundException: <co
+ xml:id="loadUserObjectNotFoundException"/>No row with the given identifier exists: [hibintro.v1.model.User#goik2]
+...
+ at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
+ at hibintro.v1.model.User_$$_javassist_0.getCname(User_$$_javassist_0.java)
+ at hibintro.v1.run.RetrieveSingleUser.main(<emphasis role="bold">RetrieveSingleUser.java:35</emphasis>)<co
+ xml:id="exceptionOnGetCname"/>
+</programlisting>
+
+ <para>Due to <coref linkend="exceptionOnGetCname"/> the
+ exception is being triggered by the <code>getCname()</code>
+ call. The documentation of <code>load()</code> tells us that
+ method calls may be delegated to proxy objects which is
+ being implemented by byte code instrumentation. If however
+ no matching database object exists calling the proxy
+ instance yields a
+ <classname>org.hibernate.ObjectNotFoundException</classname>.</para>
+
+ <para>The documentation also tells us to use the
+ corresponding <methodname>get()</methodname> method which
+ actually returns <code>null</code> in case a primary key
+ value does not exist:</para>
+
+ <programlisting>... final User u = (User) session.get(User.class, "goik2");
+ if (null == u ) {
+ System.out.println("No such user having key value 'goik2'");
+...</programlisting>
+ </answer>
+ </qandaentry>
+ </qandadiv>
+ </qandaset>
+ </section>
+
+ <section xml:id="loadingObjectsByQuery">
+ <title>Loading objects by queries</title>
+
+ <para>Often we are interested in a (sub)set of results. We populate
+ our database with additional
<classname>hibintro.v1.model.User</classname> instances:</para>
<programlisting>package hibintro.v1.run;
@@ -16026,8 +16094,10 @@ public class PersistUsers {
xlink:href="http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch16.html">HQL</abbrev>)
for object queries. As we will see <abbrev
xlink:href="http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch16.html">HQL</abbrev>
- extents SQL with respect to polymorphic queries. The current example
- does not use inheritance leaving us with a simple <abbrev
+ extends <acronym
+ xlink:href="http://en.wikipedia.org/wiki/Sql">SQL</acronym> with
+ respect to polymorphic queries. The current example does not use
+ inheritance leaving us with a simple <abbrev
xlink:href="http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch16.html">HQL</abbrev>
query <coref linkend="hqlFromUser"/> in
<classname>hibintro.v1.run.RetrieveAll</classname>:</para>
@@ -16049,19 +16119,83 @@ final List<User> users = (List<User>) searchUsers.list();
}</programlisting>
</figure>
- <para>This yields the expected result:</para>
+ <para>Being used to <acronym
+ xlink:href="http://en.wikipedia.org/wiki/Sql">SQL</acronym>we notice
+ the absence of a SELECT clause in <coref linkend="hqlFromUser"/>:
+ The ratio behind is having a focus on objects rather than on
+ attribute sets. Thus our <abbrev
+ xlink:href="http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch16.html">HQL</abbrev>
+ query returns a set of <classname>hibintro.v1.model.User</classname>
+ instances:</para>
<programlisting>uid=eve, Eve Briggs
uid=goik, Martin Goik
uid=wings, Fred Wings</programlisting>
- <para>The careful reader may already have expected <abbrev
+ <qandaset role="exercise">
+ <qandadiv>
+ <qandaentry>
+ <question>
+ <para>We may actually retrieve attributes rather than
+ objects. For this purpose our query actually resembles
+ standard <acronym
+ xlink:href="http://en.wikipedia.org/wiki/Sql">SQL</acronym><coref
+ linkend="hqlWithSelect"/>:</para>
+
+ <programlisting>final Query searchUsers = session.createQuery("<emphasis
+ role="bold">select uid, cname from User</emphasis>" <co
+ xml:id="hqlWithSelect"/>);
+final Object queryResult <co xml:id="queryResultFromSelect"/>= searchUsers.list();</programlisting>
+
+ <para>Use the <methodname>getSimpleName()</methodname>
+ reflection method to iteratively analyze the
+ <code>queryResult</code> <coref
+ linkend="queryResultFromSelect"/> instance's structure. This
+ guides you in finding suitable casts to add code similar as
+ in <xref linkend="retrieveAllUserByHql"/> in order to write
+ user's attribute values to standard output.</para>
+ </question>
+
+ <answer>
+ <para>A possible implementation reads:</para>
+
+ <programlisting>package hibintro.v1.run;
+...
+public class GetUsersAsAttributes {
+...
+ final Query searchUsers = session.createQuery("<emphasis role="bold">select uid, cname from User</emphasis>");
+
+ @SuppressWarnings("unchecked")
+ final Object queryResult = searchUsers.list();
+ System.out.println("queryResult type:" + queryResult.getClass().getSimpleName()); <co
+ xml:id="typeOfHqlResult"/>
+ final List<Object> usersAttributes = (List<Object>) queryResult;
+ for (final Object o: usersAttributes) {
+ System.out.println("result set element type:" + o.getClass().getSimpleName()); <co
+ xml:id="typeOfEmbeddedObjects"/>
+ final Object attributes[] = (Object []) o;
+ for (Object attribute: attributes) {
+ System.out.println("attribute value:" + attribute);
+ }
+ }...</programlisting>
+
+ <para>Actually the two lines <coref
+ linkend="typeOfHqlResult"/> and <coref
+ linkend="typeOfEmbeddedObjects"/> are only needed during the
+ development process to discover the result set's object
+ structure.</para>
+ </answer>
+ </qandaentry>
+ </qandadiv>
+ </qandaset>
+
+ <para>The careful reader may already expect <abbrev
xlink:href="http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch16.html">HQL</abbrev>
- to offer additional features. Following
- <classname>hibintro.v1.run.SelectUser</classname> we may restrict
- our result set by an <acronym
+ to offer additional features namely predicate based queries.
+ Following <classname>hibintro.v1.run.SelectUser</classname> we may
+ restrict our result set by an <acronym
xlink:href="http://en.wikipedia.org/wiki/Sql">SQL</acronym> style
- <code>where</code> clause:</para>
+ <code>WHERE</code> clause:</para>
<programlisting> final List<User> users = (List<User>) session.createQuery(
"<emphasis role="bold">from User u where u.cname like '%e%'</emphasis>").list();
@@ -16075,6 +16209,18 @@ uid=wings, Fred Wings</programlisting>
<programlisting>Found user 'Eve Briggs'
Found user 'Fred Wings'</programlisting>
</section>
+
+ <section xml:id="criteriaBasedQueries">
+ <title>Criteria based queries</title>
+
+ <para>Selecting Objects by <abbrev
+ xlink:href="http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch16.html">HQL</abbrev>c
+ queries technically means parsing <abbrev
+ xlink:href="http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html/ch16.html">HQL</abbrev>
+ and transforming it into some sort of abstract syntax tree. We may
+ instead create corresponding structures by using
+ <trademark>Hibernate</trademark>'s criteria API:</para>
+ </section>
</section>
<section xml:id="mappingSingleClasses">
diff --git a/ws/eclipse/HibIntro/src/main/java/hibintro/v1/run/GetUsersAsAttributes.java b/ws/eclipse/HibIntro/src/main/java/hibintro/v1/run/GetUsersAsAttributes.java
new file mode 100644
index 000000000..1b7bd8d99
--- /dev/null
+++ b/ws/eclipse/HibIntro/src/main/java/hibintro/v1/run/GetUsersAsAttributes.java
@@ -0,0 +1,48 @@
+package hibintro.v1.run;
+
+
+
+import hibintro.util.HibernateUtil;
+import hibintro.v1.model.User;
+
+import java.util.List;
+
+import org.hibernate.Query;
+import org.hibernate.Session;
+import org.hibernate.Transaction;
+
+/**
+ * @author goik
+ *
+ * Retrieval all {@link User} attributes from a database.
+ *
+ */
+public class GetUsersAsAttributes {
+
+ /**
+ * Retrieving a single {@link User} instance by means
+ * of its primary key value "goik".
+ * @param args unused
+ */
+ public static void main(String[] args) {
+ final Session session = HibernateUtil.createSessionFactory("hibernate.cfg.xml").openSession();
+
+ final Transaction transaction = session.beginTransaction();
+
+ final Query searchUsers = session.createQuery("select uid, cname from User");
+
+ @SuppressWarnings("unchecked")
+ final Object queryResult = searchUsers.list();
+ System.out.println("queryResult type:" + queryResult.getClass().getSimpleName());
+ final List<Object> usersAttributes = (List<Object>) queryResult;
+ for (final Object o: usersAttributes) {
+ System.out.println("result set element type:" + o.getClass().getSimpleName());
+ final Object attributes[] = (Object []) o;
+ for (Object attribute: attributes) {
+ System.out.println("attribute value:" + attribute);
+ }
+ }
+
+ transaction.commit();
+ }
+}
\ No newline at end of file
diff --git a/ws/eclipse/HibIntro/src/main/java/hibintro/v1/run/RetrieveAllByCriteria.java b/ws/eclipse/HibIntro/src/main/java/hibintro/v1/run/RetrieveAllByCriteria.java
new file mode 100644
index 000000000..f5b07823a
--- /dev/null
+++ b/ws/eclipse/HibIntro/src/main/java/hibintro/v1/run/RetrieveAllByCriteria.java
@@ -0,0 +1,46 @@
+package hibintro.v1.run;
+
+
+
+import hibintro.util.HibernateUtil;
+import hibintro.v1.model.User;
+
+import java.util.List;
+
+import org.hibernate.Query;
+import org.hibernate.Session;
+import org.hibernate.Transaction;
+
+
+
+/**
+ * @author goik
+ *
+ * Retrieval of all {@link User} objects from a database.
+ *
+ */
+public class RetrieveAllByCriteria {
+
+ /**
+ * Retrieving users containing the letter <code>r</code> in
+ * {@link User#getCname()}.
+ *
+ * @param args
+ */
+ public static void main(String[] args) {
+ final Session session = HibernateUtil.createSessionFactory("hibernate.cfg.xml").openSession();
+
+ //final Criteria crit = session.createCriteria(Cat.class);
+
+ final Transaction transaction = session.beginTransaction();
+
+ final Query searchUsers = session.createQuery("from User");
+ @SuppressWarnings("unchecked")
+ final List<User> users = (List<User>) searchUsers.list();
+ for (final User u: users) {
+ System.out.println("uid=" + u.getUid() + ", " + u.getCname());
+ }
+
+ transaction.commit();
+ }
+}
\ No newline at end of file
--
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