Add support for 'constant_keyword'

Author: sethmlarson

elasticsearch_dsl/field.py

@@ -316,6 +316,10 @@ class Keyword(Field):
     name = "keyword"
 
 
+class ConstantKeyword(Keyword):
+    name = "constant_keyword"
+
+
 class Boolean(Field):
     name = "boolean"
     _coerce = True

tests/test_field.py

@@ -172,6 +172,11 @@ def test_binary():
     assert f.deserialize(None) is None
 
 
+def test_constant_keyword():
+    f = field.ConstantKeyword()
+    assert f.to_dict() == {"type": "constant_keyword"}
+
+
 def test_object_dynamic_values():
     for dynamic in True, False, "strict":
         f = field.Object(dynamic=dynamic)