fix: make database function compatible with postgresql and mysql both

openedx_tagging/core/tagging/models/utils.py

@@ -3,6 +3,7 @@
 """
 from django.db.models import Aggregate, CharField
 from django.db.models.expressions import Func
+from django.db import connection as db_connection
 
 RESERVED_TAG_CHARS = [
     '\t',  # Used in the database to separate tag levels in the "lineage" field
@@ -34,21 +35,59 @@ def as_sqlite(self, compiler, connection, **extra_context):
         )
 
 
-class StringAgg(Aggregate):  # pylint: disable=abstract-method
+from django.db.models import Aggregate, CharField
+from django.db.models.expressions import Combinable
+
+class StringAgg(Aggregate, Combinable):
     """
     Aggregate function that collects the values of some column across all rows,
-    and creates a string by concatenating those values, with "," as a separator.
+    and creates a string by concatenating those values, with a specified separator.
 
-    This is the same as Django's django.contrib.postgres.aggregates.StringAgg,
-    but this version works with MySQL and SQLite.
+    This version supports PostgreSQL (STRING_AGG), MySQL (GROUP_CONCAT), and SQLite.
     """
+    # Default function is for MySQL (GROUP_CONCAT)
     function = 'GROUP_CONCAT'
     template = '%(function)s(%(distinct)s%(expressions)s)'
 
-    def __init__(self, expression, distinct=False, **extra):
+    def __init__(self, expression, distinct=False, delimiter=',', **extra):
+        self.delimiter = delimiter
+        # Handle the distinct option and output type
+        distinct_str = 'DISTINCT ' if distinct else ''
+
+        extra.update(dict(
+            distinct=distinct_str,
+            output_field=CharField()
+        ))
+
+        # Check the database backend (PostgreSQL, MySQL, or SQLite)
+        if 'postgresql' in db_connection.vendor.lower():
+            self.function = 'STRING_AGG'
+            self.template = '%(function)s(%(distinct)s%(expressions)s, %(delimiter)s)'
+            extra.update({"delimiter": delimiter})
+
+        # Initialize the parent class with the necessary parameters
         super().__init__(
             expression,
-            distinct='DISTINCT ' if distinct else '',
-            output_field=CharField(),
             **extra,
         )
+
+    def as_sql(self, compiler, connection, **extra_context):
+        # If PostgreSQL, we use STRING_AGG with a separator
+        if 'postgresql' in connection.vendor.lower():
+            # Ensure that expressions are cast to TEXT for PostgreSQL
+            expressions_sql, params = compiler.compile(self.source_expressions[0])
+            expressions_sql = f"({expressions_sql})::TEXT"  # Cast to TEXT for PostgreSQL
+            return f"{self.function}({expressions_sql}, {self.delimiter!r})", params
+        else:
+            # MySQL/SQLite handles GROUP_CONCAT with SEPARATOR
+            return super().as_sql(compiler, connection, **extra_context)
+
+    # Implementing abstract methods from Combinable
+    def __rand__(self, other):
+        return self._combine(other, 'AND', is_combinable=True)
+
+    def __ror__(self, other):
+        return self._combine(other, 'OR', is_combinable=True)
+
+    def __rxor__(self, other):
+        return self._combine(other, 'XOR', is_combinable=True)