improve javadoc for @view, @subselect, and @SQLSelect

Author: gavinking

hibernate-core/src/main/java/org/hibernate/annotations/SQLSelect.java

@@ -34,6 +34,22 @@
  * <li>the foreign key, in the case of a collection.
  * </ol>
  * <p>
+ * If the {@linkplain #querySpaces tables which affect the query results}
+ * are specified, then changes to those tables will be flushed before
+ * execution of the query.
+ * <p>
+ * For example:
+ * <pre>
+ * &#64;SQLSelect(sql = """
+ *                  SELECT id, created, text
+ *                  FROM records
+ *                  WHERE id = ? and deleted is null
+ *                  """
+ *            querySpaces = "records")
+ * &#64;Entity
+ * public class Record { ... }
+ * </pre>
+ * <p>
  * Optionally, an explicit {@linkplain #resultSetMapping result set mapping}
  * may be specified. It should have:
  * <ol>

hibernate-core/src/main/java/org/hibernate/annotations/Subselect.java

@@ -11,20 +11,49 @@
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
 
 /**
- * Maps an immutable and read-only entity to a given SQL {@code select} expression.
+ * Maps an {@linkplain Immutable immutable} and read-only entity to a given
+ * SQL {@code select} expression.
  * <p>
- * This is an alternative to defining a database view and mapping the entity to
- * the view using the {@link jakarta.persistence.Table @Table} annotation.
+ * For example:
+ * <pre>
+ * &#64;Immutable &#64;Entity
+ * &#64;Subselect("""
+ *            select type, sum(amount) as total, avg(amount) as average
+ *            from details
+ *            group by type
+ *            """)
+ * &#64;Synchronize("details")
+ * public class Summary {
+ *     &#64;Id String type;
+ *     Double total;
+ *     Double average;
+ * }
+ * </pre>
+ * <p>
+ * This is an alternative to defining a {@linkplain View view} and mapping
+ * the entity to the view using the {@link jakarta.persistence.Table @Table}
+ * annotation.
+ * <p>
+ * It's possible to have an entity class which maps a table, and another
+ * entity which is defined by a {@code @Subselect} involving the same table.
+ * In this case, a stateful session is vulnerable to data aliasing effects,
+ * and it's the responsibility of client code to ensure that changes to the
+ * first entity are flushed to the database before reading the same data via
+ * the second entity. The {@link Synchronize @Synchronize} annotation can
+ * help alleviate this problem, but it's an incomplete solution. We therefore
+ * recommend the use of {@linkplain org.hibernate.StatelessSession stateless
+ * sessions} in this situation.
  *
  * @see Synchronize
+ * @see View
  *
  * @author Sharath Reddy
  */
 @Target(TYPE)
 @Retention(RUNTIME)
 public @interface Subselect {
 	/**
-	 * The query.
+	 * The subquery, written in native SQL.
 	 */
 	String value();
 }

hibernate-core/src/main/java/org/hibernate/annotations/Synchronize.java

@@ -25,7 +25,7 @@
  * Ordinarily, Hibernate knows the tables containing the state of an
  * entity or collection. This annotation might be necessary if:
  * <ul>
- * <li>an entity or collection maps a database view,
+ * <li>an entity or collection maps a database {@linkplain View view},
  * <li>an entity or collection is persisted using handwritten SQL,
  *     that is, using {@link SQLSelect @SQLSelect} and friends, or
  * <li>an entity is mapped using {@link Subselect @Subselect}.
@@ -41,6 +41,9 @@
  * @author Sharath Reddy
  *
  * @see org.hibernate.query.SynchronizeableQuery
+ * @see View
+ * @see Subselect
+ * @see SQLSelect
  */
 @Target({TYPE, FIELD, METHOD})
 @Retention(RUNTIME)

hibernate-core/src/main/java/org/hibernate/annotations/View.java

@@ -26,19 +26,24 @@
  * <pre>
  * &#64;Immutable &#64;Entity
  * &#64;Table(name="summary")
- * &#64;View(query="select type, sum(amount) as total, avg(amount) as average from details group by type")
+ * &#64;View(query="""
+ *             select type, sum(amount) as total, avg(amount) as average
+ *             from details
+ *             group by type
+ *             """)
  * &#64;Synchronize("details")
  * public class Summary {
  *     &#64;Id String type;
  *     Double total;
  *     Double average;
  * }
  * </pre>
- * <p>
  * results in the following generated DDL:
  * <pre>
  * create view summary
- * as select type, sum(amount) as total, avg(amount) as average from details group by type
+ * as select type, sum(amount) as total, avg(amount) as average
+ *    from details
+ *    group by type
  * </pre>
  * <p>
  * If a view is not updatable, we recommend annotating the
@@ -47,7 +52,7 @@
  * It's possible to have an entity class which maps a table,
  * and another entity which maps a view defined as a query
  * against that table. In this case, a stateful session is
- * vulnerable to data aliasing effects, and it is the
+ * vulnerable to data aliasing effects, and it's the
  * responsibility of client code to ensure that changes to
  * the first entity are flushed to the database before
  * reading the same data via the second entity. The
@@ -61,6 +66,8 @@
  * @since 6.3
  *
  * @author Gavin King
+ *
+ * @see Synchronize
  */
 @Incubating
 @Target(TYPE)