[ADD] util.convert_many2one_field_to_many2many

src/util/fields.py

@@ -51,6 +51,7 @@ def make_index_name(table_name, column_name):
     alter_column_type,
     column_exists,
     column_type,
+    create_m2m,
     explode_execute,
     explode_query_range,
     format_query,
@@ -60,6 +61,7 @@ def make_index_name(table_name, column_name):
     pg_text2html,
     remove_column,
     table_exists,
+    target_of,
 )
 from .records import _remove_import_export_paths
 from .report import add_to_migration_reports, get_anchor_link_to_record
@@ -731,6 +733,49 @@ def convert_field_to_html(cr, model, field, skip_inherit=()):
         convert_field_to_html(cr, inh.model, field, skip_inherit=skip_inherit)
 
 
+def convert_many2one_field_to_many2many(cr, model, field, new_name=None, m2m_table=None, col1=None, col2=None):
+    _validate_model(model)
+    if new_name is None:
+        if not field.endswith("_id"):
+            raise ValueError("Please specify the new name explicitly")
+        new_name = field + "s"
+
+    table1 = table_of_model(cr, model)
+    table2, _, _ = target_of(cr, table1, field)
+
+    if m2m_table is None:
+        m2m_table = "{}_{}_rel".format(*sorted([table1, table2]))
+
+    if col1 is None:
+        col1 = "{}_id".format(table1)
+    if col2 is None:
+        col2 = "{}_id".format(table2)
+
+    create_m2m(cr, m2m_table, table1, table2, col1, col2)
+
+    fill_query = format_query(
+        cr,
+        """
+            INSERT INTO {m2m}({col1}, {col2})
+                 SELECT id, {field}
+                   FROM {table}
+                  WHERE {field} IS NOT NULL
+        """,
+        m2m=m2m_table,
+        col1=col1,
+        col2=col2,
+        field=field,
+        table=table1,
+    )
+    cr.execute(fill_query)
+    remove_column(cr, table1, field)
+    rename_field(cr, model, field, new_name)
+
+
+# Because we can.
+m2o2m2m = convert_many2one_field_to_many2many
+
+
 def _convert_field_to_company_dependent(
     cr, model, field, type, target_model=None, default_value=None, default_value_ref=None, company_field="company_id"
 ):