sql: add method to load evolutions in batch (#7015)

tests/test_sql.py

@@ -254,6 +254,27 @@ def test_sql_evolution_change():
     assert len(formdata.evolution) == 2
     assert formdata.evolution[-1].comment == 'foobar'
 
+@postgresql
+def test_sql_multiple_evolutions():
+    data_class = formdef.data_class(mode='sql')
+    for i in range(20):
+        formdata = data_class()
+        formdata.just_created()
+        formdata.store()
+        id = formdata.id
+
+        formdata = data_class.get(id)
+
+        evo = Evolution()
+        evo.time = time.localtime()
+        evo.status = formdata.status
+        evo.comment = 'hello world %d' % i
+        formdata.evolution.append(evo)
+        formdata.store()
+
+    values = data_class.select()
+    data_class.load_all_evolutions(values)
+    assert [x._evolution for x in values]
 
 @postgresql
 def test_sql_get_ids_with_indexed_value():

wcs/backoffice/root.py

@@ -1116,6 +1116,10 @@ class FormPage(Directory):
         do_graphs = get_publisher().is_using_postgresql()
 
         values = self.formdef.data_class().select(criterias)
+        if get_publisher().is_using_postgresql():
+            # load all evolutions in a single batch, to avoid as many query as
+            # there are formdata when computing resolution times statistics.
+            self.formdef.data_class().load_all_evolutions(values)
 
         r += htmltext('<div id="statistics">')
         if do_graphs:

wcs/sql.py

@@ -883,6 +883,40 @@ class SqlFormData(SqlMixin, wcs.formdata.FormData):
 
     evolution = property(get_evolution, set_evolution)
 
+
+    @guard_postgres
+    def load_all_evolutions(cls, values):
+        # Typically formdata.evolution is loaded on-demand (see above
+        # property()) and this is fine to minimize queries, especially when
+        # dealing with a single formdata.  However in some places (to compute
+        # statistics for example) it is sometimes useful to access .evolution
+        # on a serie of formdata and in that case, it's more efficient to
+        # optimize the process loading all evolutions in a single batch query.
+        object_dict = dict([(x.id, x) for x in values if x.id and x._evolution is None])
+        conn, cur = get_connection_and_cursor()
+        sql_statement = '''SELECT id, who, status, time, comment, parts, formdata_id
+                             FROM %s_evolutions''' % cls._table_name
+        sql_statement += ''' WHERE formdata_id IN %(object_ids)s ORDER BY id'''
+        cur.execute(sql_statement, {'object_ids': tuple(object_dict.keys())})
+
+        for value in values:
+            value._evolution = []
+
+        while True:
+            row = cur.fetchone()
+            if row is None:
+                break
+            _sql_id, who, status, time, comment, parts, formdata_id = tuple(row[:7])
+            formdata = object_dict.get(formdata_id)
+            if not formdata:
+                continue
+            formdata._evolution.append(formdata._row2evo(row))
+
+        conn.commit()
+        cur.close()
+    load_all_evolutions = classmethod(load_all_evolutions)
+
+
     @guard_postgres
     def store(self):
         sql_dict = {