XWIKI-13700: The document tree is still slow on MySql

* Fix query on PostgreSQL (PSQLException: ERROR: operator does not exist: boolean <> integer)

xwiki-platform-core/xwiki-platform-index/xwiki-platform-index-tree/xwiki-platform-index-tree-api/src/main/java/org/xwiki/index/tree/internal/nestedpages/query/HiddenPageFilter.java

@@ -19,11 +19,16 @@
  */
 package org.xwiki.index.tree.internal.nestedpages.query;
 
+import javax.inject.Inject;
 import javax.inject.Named;
 import javax.inject.Singleton;
 
+import org.hibernate.dialect.Dialect;
+import org.hibernate.engine.SessionFactoryImplementor;
 import org.xwiki.component.annotation.Component;
 
+import com.xpn.xwiki.store.hibernate.HibernateSessionFactory;
+
 /**
  * Filters hidden pages. This filter works with the named <strong>native SQL</strong> queries declared in the
  * {@code queries.hbm.xml} mapping file.
@@ -36,17 +41,42 @@
 @Singleton
 public class HiddenPageFilter extends AbstractNestedPageFilter
 {
+    @Inject
+    private HibernateSessionFactory sessionFactory;
+
     @Override
     protected String filterNestedPagesStatement(String statement)
     {
         // The constraint is different depending on whether we filter a native SQL query or an HQL query.
-        String constraint = statement.indexOf("XWS_REFERENCE") < 0 ? "hidden <> true " : "XWS_HIDDEN <> 1 ";
+        String constraint =
+            statement.indexOf("XWS_REFERENCE") < 0 ? "hidden <> true " : getHiddenConstraint("XWS_HIDDEN");
         return insertWhereConstraint(statement, constraint);
     }
 
     @Override
     protected String filterTerminalPagesStatement(String statement)
     {
-        return statement + " and doc.XWD_HIDDEN <> 1 ";
+        return statement + " and " + getHiddenConstraint("doc.XWD_HIDDEN");
+    }
+
+    private String getHiddenConstraint(String field)
+    {
+        // I don't know exactly why "field = false" is not enough since the hidden field is marked as non-null so it
+        // should have only two values (true or false). I remember something related to Oracle but I don't know for
+        // sure. Let's keep this for now, but the downside of using the <> (not-equal) operator instead of = (equal) is
+        // that the database cannot use the index so the query is slower (which can be significant when we have
+        // thousands of documents and spaces in the database).
+        //
+        // Note that we can't use the boolean literal here because Oracle doesn't support it (ORA-00904: "TRUE": invalid
+        // identifier) and we can't use "1" (integer) also because PostgreSQL doesn't support automatic integer to
+        // boolean conversion (PSQLException: ERROR: operator does not exist: boolean <> integer). We're forced to get
+        // the boolean value from the SQL Dialect currently in use.
+        return String.format("%s <> %s ", field, toBooleanValueString(true));
+    }
+
+    private String toBooleanValueString(boolean value)
+    {
+        Dialect dialect = ((SessionFactoryImplementor) this.sessionFactory.getSessionFactory()).getDialect();
+        return dialect.toBooleanValueString(value);
     }
 }