fix Field.__init__ (#742)

Author: WH-2099

pypika/terms.py

@@ -548,6 +548,10 @@ def __init__(
     ) -> None:
         super().__init__(alias=alias)
         self.name = name
+        if isinstance(table, str):
+            # avoid circular import at load time
+            from pypika.queries import Table
+            table = Table(table)
         self.table = table
 
     def nodes_(self) -> Iterator[NodeT]:

pypika/tests/test_terms.py

@@ -15,6 +15,13 @@ def test_when_alias_specified(self):
         self.assertEqual('bar', str(c1.alias))
 
 
+class FieldInitTests(TestCase):
+    def test_init_with_str_table(self):
+        test_table_name = "test_table"
+        field = Field(name="name", table=test_table_name)
+        self.assertEqual(field.table, Table(name=test_table_name))
+    
+
 class FieldHashingTests(TestCase):
     def test_tabled_eq_fields_equally_hashed(self):
         client_name1 = Field(name="name", table=Table("clients"))