Add template filters to convert objects to and from JSON strings (#27909)

* Added filters to convert objects to and from JSON strings.

* Added extra spacing.

* Removed try/catch to get native exceptions

* Added tests.

homeassistant/helpers/template.py

@@ -884,6 +884,16 @@ def ordinal(value):
     )
 
 
+def from_json(value):
+    """Convert a JSON string to an object."""
+    return json.loads(value)
+
+
+def to_json(value):
+    """Convert an object to a JSON string."""
+    return json.dumps(value)
+
+
 @contextfilter
 def random_every_time(context, values):
     """Choose a random value.
@@ -916,6 +926,8 @@ class TemplateEnvironment(ImmutableSandboxedEnvironment):
         self.filters["timestamp_custom"] = timestamp_custom
         self.filters["timestamp_local"] = timestamp_local
         self.filters["timestamp_utc"] = timestamp_utc
+        self.filters["to_json"] = to_json
+        self.filters["from_json"] = from_json
         self.filters["is_defined"] = fail_when_undefined
         self.filters["max"] = max
         self.filters["min"] = min

tests/helpers/test_template.py

@@ -501,6 +501,30 @@ def test_timestamp_local(hass):
         )
 
 
+def test_to_json(hass):
+    """Test the object to JSON string filter."""
+
+    # Note that we're not testing the actual json.loads and json.dumps methods,
+    # only the filters, so we don't need to be exhaustive with our sample JSON.
+    expected_result = '{"Foo": "Bar"}'
+    actual_result = template.Template(
+        "{{ {'Foo': 'Bar'} | to_json }}", hass
+    ).async_render()
+    assert actual_result == expected_result
+
+
+def test_from_json(hass):
+    """Test the JSON string to object filter."""
+
+    # Note that we're not testing the actual json.loads and json.dumps methods,
+    # only the filters, so we don't need to be exhaustive with our sample JSON.
+    expected_result = "Bar"
+    actual_result = template.Template(
+        '{{ (\'{"Foo": "Bar"}\' | from_json).Foo }}', hass
+    ).async_render()
+    assert actual_result == expected_result
+
+
 def test_min(hass):
     """Test the min filter."""
     assert template.Template("{{ [1, 2, 3] | min }}", hass).async_render() == "1"