funnydman · December 1, 2020 12:56 · Dec 1, 2020
diff --git a/combined_expressions.py b/combined_expressions.py
@@ -0,0 +1,82 @@
+# https://stackoverflow.com/questions/58877390/how-to-collect-results-into-array-from-annotation
+
+"""
+Some different ways:
+
+"""
+
+
+class CombinedExpressions(SQLiteNumericMixin, Expression):
+    def __init__(self, *expressions, connector, output_field=None):
+        super().__init__(output_field=output_field)
+        self.connector = connector
+        self.expressions = expressions
+
+    def get_source_expressions(self):
+        return self.expressions
+
+    def as_sql(self, compiler, connection):
+        output_fields = []
+        not_supported_fields = {'DateField', 'DateTimeField', 'TimeField', 'DurationField'}
+        for expr in self.expressions:
+            output_field = getattr(expr, 'output_field')
+            if output_field:
+                output_fields.append(output_field.get_internal_type())
+        if set(output_fields) & not_supported_fields:
+            raise NotImplementedError(f'Not support for such output fields: {", ".join(not_supported_fields)}')
+
+        expressions = []
+        expression_params = []
+        # compile every expression
+        for expression in self.expressions:
+            sql, params = compiler.compile(expression)
+            expressions.append(sql)
+            expression_params.extend(params)
+
+        # order of precedence
+        expression_wrapper = '(%s)'
+        sql = connection.ops.combine_expression(self.connector, expressions)
+        return expression_wrapper % sql, expression_params
+
+    def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
+        c = self.copy()
+        c.is_summary = summarize
+        # resolving stuff
+        expressions = []
+        for exp in c.expressions:
+            exp = exp.resolve_expression(query, allow_joins, reuse, summarize, for_save)
+            expressions.append(exp)
+        c.expressions = expressions
+        return c
+
+
+class FruitManager(Manager):
+    def get_queryset(self):
+        query = super().get_queryset()
+
+        query = query.annotate(
+            result=(
+                CombinedExpressions(
+                    ArrayAgg(Case(
+                        When(
+                            type='tropicals',
+                            then=Value('This fruit is tropical...'),
+
+                        ),
+                        output_field=CharField()
+                    )),
+                    ArrayAgg(Case(
+                        When(
+                            country_of_import='Africa',
+                            then=Value('This fruit is citrus...'),
+
+                        ),
+                        output_field=CharField(),
+                        default=Value('here we go')),
+                    ),
+                    connector='||'
+                )
+            )
+        )
+
+        return query