optimization: use SELECT 1 instead of SELECT count(*) (#65362)

wcs/admin/forms.py

@@ -1875,7 +1875,7 @@ class FormsDirectory(AccessControlled, Directory):
 
     def new(self):
         get_response().breadcrumb.append(('new', _('New')))
-        if get_publisher().role_class.count() == 0:
+        if not (get_publisher().role_class.exists()):
             return template.error_page(self.section, _('You first have to define roles.'))
         formdefui = self.formdef_ui_class(None)
         form = formdefui.new_form_ui()

wcs/admin/users.py

@@ -498,7 +498,7 @@ class UsersDirectory(Directory):
         # XXX: user must be logged in to get here
         user = get_publisher().user_class()
         user_ui = UserUI(user)
-        first_user = get_publisher().user_class.count() == 0
+        first_user = not (get_publisher().user_class.exists())
         if first_user:
             user.is_admin = first_user
         form = user_ui.form()

wcs/api.py

@@ -428,7 +428,7 @@ class ApiFormsDirectory(Directory):
         if get_request().form.get('full') == 'on':
             raise RequestError('no such parameter "full"')
 
-        if FormDef.count() == 0:
+        if not (FormDef.exists()):
             # early return, this avoids running a query against a missing SQL view.
             get_response().set_content_type('application/json')
             return json.dumps({'data': []}, cls=misc.JSONEncoder)
@@ -908,7 +908,7 @@ class ApiUserDirectory(Directory):
         return json.dumps(user_info, cls=misc.JSONEncoder)
 
     def get_user_forms(self, user):
-        if FormDef.count() == 0:
+        if not (FormDef.exists()):
             # early return, this avoids running a query against a missing SQL view.
             return []
 

wcs/backoffice/data_management.py

@@ -92,7 +92,7 @@ class DataManagementDirectory(ManagementDirectory):
 
     def _q_index(self):
         html_top('data_management', _('Cards'))
-        if CardDef.count() == 0:
+        if not (CardDef.exists()):
             return self.empty_site_message(_('Cards'))
         return template.QommonTemplateResponse(
             templates=['wcs/backoffice/data-management.html'], context={'view': self}

wcs/backoffice/management.py

@@ -409,7 +409,7 @@ class ManagementDirectory(Directory):
         html_top('management', _('Global statistics'))
         get_response().breadcrumb.append(('statistics', _('Global statistics')))
 
-        if FormDef.count() == 0:
+        if not (FormDef.exists()):
             r = TemplateIO(html=True)
             r += htmltext('<div class="top-title">')
             r += htmltext('<h2>%s</h2>') % _('Global statistics')
@@ -605,7 +605,7 @@ class ManagementDirectory(Directory):
 
         html_top('management', _('Management'))
 
-        if FormDef.count() == 0:
+        if not (FormDef.exists()):
             return self.empty_site_message(_('Global View'))
 
         limit = misc.get_int_or_400(
@@ -733,7 +733,7 @@ class ManagementDirectory(Directory):
     def count(self):
         if not get_publisher().is_using_postgresql():
             raise errors.TraversalError()
-        if FormDef.count() == 0:
+        if not (FormDef.exists()):
             return misc.json_response({'count': 0})
         from wcs import sql
 
@@ -853,7 +853,7 @@ class FormPage(Directory):
     def check_access(self, api_name=None):
         session = get_session()
         user = get_request().user
-        if user is None and get_publisher().user_class.count() == 0:
+        if user is None and not (get_publisher().user_class.exists()):
             user = get_publisher().user_class()
             user.is_admin = True
         if not user:

wcs/backoffice/root.py

@@ -92,7 +92,7 @@ class RootDirectory(BackofficeRootDirectory):
             return True
 
         if not get_request().user:
-            if get_publisher().user_class.count() == 0:
+            if not (get_publisher().user_class.exists()):
                 # setting up the site, access is granted to settings and users
                 # sections
                 return subdirectory in ('settings', 'users')
@@ -146,7 +146,7 @@ class RootDirectory(BackofficeRootDirectory):
             get_response().filter['admin_for_all'] = True
             return
 
-        if get_publisher().user_class.count() > 0:
+        if get_publisher().user_class.exists():
             user = req.user
             if not user:
                 raise errors.AccessUnauthorizedError(

wcs/formdef.py

@@ -466,7 +466,7 @@ class FormDef(StorableObject):
             # or if there are not yet any submitted forms (or if site
             # is using the SQL storage as internal identifier is not used
             # in that mode.
-            if self.id is None or get_publisher().is_using_postgresql() or self.data_class().count() == 0:
+            if self.id is None or get_publisher().is_using_postgresql() or not (self.data_class().exists()):
                 self.internal_identifier = new_internal_identifier
         object_only = kwargs.pop('object_only', False)
 

wcs/qommon/ident/idp.py

@@ -200,7 +200,7 @@ class MethodDirectory(Directory):
             user.set_attributes_from_formdata(data)
             user.form_data = data
 
-        if get_publisher().user_class.count() == 0:
+        if not (get_publisher().user_class.exists()):
             user.is_admin = True
 
         session = get_session()

wcs/qommon/ident/password.py

@@ -592,7 +592,7 @@ class MethodDirectory(Directory):
             if identities_cfg.get('email-as-username', False):
                 user.email = username
 
-        if get_publisher().user_class.count() == 0:
+        if not (get_publisher().user_class.exists()):
             user.is_admin = True
         user.store()
 

wcs/qommon/storage.py

@@ -456,6 +456,10 @@ class StorableObject:
             return len(cls.select(clause))
         return len(cls.keys())
 
+    @classmethod
+    def exists(cls, clause=None):
+        return bool(cls.count(clause))
+
     @classmethod
     def sort_results(cls, objects, order_by):
         if not order_by:

wcs/sql.py

@@ -1878,6 +1878,25 @@ class SqlMixin:
         cur.close()
         return count
 
+    @classmethod
+    @guard_postgres
+    def exists(cls, clause=None):
+        where_clauses, parameters, func_clause = parse_clause(clause)
+        if func_clause:
+            # fallback to counting the result of a select()
+            return len(cls.select(clause))
+        sql_statement = 'SELECT 1 FROM %s' % cls._table_name
+        if where_clauses:
+            sql_statement += ' WHERE ' + ' AND '.join(where_clauses)
+        sql_statement += ' LIMIT 1'
+        conn, cur = get_connection_and_cursor()
+        cur.execute(sql_statement, parameters)
+        check = cur.fetchone()
+        result = check is not None
+        conn.commit()
+        cur.close()
+        return result
+
     @classmethod
     @guard_postgres
     def get_with_indexed_value(