Add JSON type compiler support

Fixes #399

Author: SandeepAkode

sqlalchemy_bigquery/_types.py

@@ -47,6 +47,7 @@
     "STRUCT": STRUCT,
     "TIMESTAMP": sqlalchemy.types.TIMESTAMP,
     "TIME": sqlalchemy.types.TIME,
+    "JSON": sqlalchemy.types.JSON,
 }
 
 # By convention, dialect-provided types are spelled with all upper case.
@@ -66,6 +67,7 @@
 STRING = _type_map["STRING"]
 TIMESTAMP = _type_map["TIMESTAMP"]
 TIME = _type_map["TIME"]
+JSON = _type_map["JSON"]
 
 try:
     _type_map["GEOGRAPHY"] = GEOGRAPHY

sqlalchemy_bigquery/base.py

@@ -641,6 +641,9 @@ def visit_NUMERIC(self, type_, **kw):
 
     visit_DECIMAL = visit_NUMERIC
 
+    def visit_JSON(self, type_, **kw):
+        return "JSON"
+
 
 class BigQueryDDLCompiler(DDLCompiler):
     option_datatype_mapping = {