Add default param for array_agg

CHANGES.rst

@@ -4,10 +4,11 @@ Changelog
 Here you can see the full list of changes between each SQLAlchemy-Utils release.
 
 
-0.30.9 (2015-06-05)
+0.30.9 (2015-06-08)
 ^^^^^^^^^^^^^^^^^^^
 
 - Added get_type utility function
+- Added default parameter for array_agg function
 
 
 0.30.8 (2015-06-05)

sqlalchemy_utils/__init__.py

@@ -8,7 +8,7 @@ from .asserts import (  # noqa
 )
 from .exceptions import ImproperlyConfigured  # noqa
 from .expression_parser import ExpressionParser  # noqa
-from .expressions import array_agg, Asterisk, row_to_json  # noqa
+from .expressions import Asterisk, row_to_json  # noqa
 from .functions import (  # noqa
     analyze,
     create_database,

sqlalchemy_utils/expressions.py

@@ -1,5 +1,5 @@
 import sqlalchemy as sa
-from sqlalchemy.dialects.postgresql import ARRAY, JSON
+from sqlalchemy.dialects.postgresql import array, ARRAY, JSON
 from sqlalchemy.ext.compiler import compiles
 from sqlalchemy.sql.expression import (
     _literal_as_text,
@@ -116,14 +116,21 @@ class array_agg(GenericFunction):
     name = 'array_agg'
     type = ARRAY
 
-    def __init__(self, arg, **kw):
+    def __init__(self, arg, default=None, **kw):
         self.type = ARRAY(arg.type)
+        self.default = default
         GenericFunction.__init__(self, arg, **kw)
 
 
 @compiles(array_agg, 'postgresql')
 def compile_array_agg(element, compiler, **kw):
-    return "%s(%s)" % (element.name, compiler.process(element.clauses))
+    compiled = "%s(%s)" % (element.name, compiler.process(element.clauses))
+    if element.default is None:
+        return compiled
+    return str(sa.func.coalesce(
+        sa.text(compiled),
+        sa.cast(array(element.default), element.type)
+    ).compile(compiler))
 
 
 class Asterisk(ColumnElement):

tests/functions/test_get_type.py

@@ -2,7 +2,6 @@ import sqlalchemy as sa
 from sqlalchemy.ext.declarative import declarative_base
 
 from sqlalchemy_utils import get_type
-from tests import TestCase
 
 
 class TestGetType(object):

tests/test_expressions.py

@@ -2,7 +2,7 @@ import sqlalchemy as sa
 from pytest import raises
 from sqlalchemy.dialects import postgresql
 
-from sqlalchemy_utils import array_agg, Asterisk, row_to_json
+from sqlalchemy_utils import Asterisk, row_to_json
 from sqlalchemy_utils.expressions import explain, explain_analyze
 from tests import TestCase
 
@@ -129,10 +129,10 @@ class TestRowToJson(object):
 class TestArrayAgg(object):
     def test_compiler_with_default_dialect(self):
         with raises(sa.exc.CompileError):
-            str(array_agg(sa.text('u.name')))
+            str(sa.func.array_agg(sa.text('u.name')))
 
     def test_compiler_with_postgresql(self):
-        assert str(array_agg(sa.text('u.name')).compile(
+        assert str(sa.func.array_agg(sa.text('u.name')).compile(
             dialect=postgresql.dialect()
         )) == "array_agg(u.name)"
 
@@ -141,3 +141,17 @@ class TestArrayAgg(object):
             sa.func.array_agg(sa.text('u.name')).type,
             postgresql.ARRAY
         )
+
+    def test_array_agg_with_default(self):
+        Base = sa.ext.declarative.declarative_base()
+
+        class Article(Base):
+            __tablename__ = 'article'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+        assert str(sa.func.array_agg(Article.id, [1]).compile(
+            dialect=postgresql.dialect()
+        )) == (
+            'coalesce(array_agg(article.id), CAST(ARRAY[%(param_1)s]'
+            ' AS INTEGER[]))'
+        )