Serialize true false (#2538)

<!--
Thanks for opening a pull request!
-->

<!-- In the case this PR will resolve an issue, please replace
${GITHUB_ISSUE_ID} below with the actual Github issue id. -->
Closes #2521

# Rationale for this change
Make true/false expression serializable

## Are these changes tested?
yes

## Are there any user-facing changes?

<!-- In the case of user-facing changes, please add the changelog label.
-->

Author: nathanbijleveld

pyiceberg/expressions/__init__.py

@@ -39,7 +39,7 @@
     literal,
 )
 from pyiceberg.schema import Accessor, Schema
-from pyiceberg.typedef import L, StructProtocol
+from pyiceberg.typedef import IcebergRootModel, L, StructProtocol
 from pyiceberg.types import DoubleType, FloatType, NestedField
 from pyiceberg.utils.singleton import Singleton
 
@@ -361,10 +361,14 @@ def __getnewargs__(self) -> Tuple[BooleanExpression]:
         """Pickle the Not class."""
         return (self.child,)
 
+    """TRUE expression."""
+
 
-class AlwaysTrue(BooleanExpression, Singleton):
+class AlwaysTrue(BooleanExpression, Singleton, IcebergRootModel[str]):
     """TRUE expression."""
 
+    root: str = "true"
+
     def __invert__(self) -> AlwaysFalse:
         """Transform the Expression into its negated version."""
         return AlwaysFalse()
@@ -378,9 +382,11 @@ def __repr__(self) -> str:
         return "AlwaysTrue()"
 
 
-class AlwaysFalse(BooleanExpression, Singleton):
+class AlwaysFalse(BooleanExpression, Singleton, IcebergRootModel[str]):
     """FALSE expression."""
 
+    root: str = "false"
+
     def __invert__(self) -> AlwaysTrue:
         """Transform the Expression into its negated version."""
         return AlwaysTrue()
@@ -732,14 +738,14 @@ def bind(self, schema: Schema, case_sensitive: bool = True) -> BoundLiteralPredi
 
         if isinstance(lit, AboveMax):
             if isinstance(self, (LessThan, LessThanOrEqual, NotEqualTo)):
-                return AlwaysTrue()  # type: ignore
+                return AlwaysTrue()
             elif isinstance(self, (GreaterThan, GreaterThanOrEqual, EqualTo)):
-                return AlwaysFalse()  # type: ignore
+                return AlwaysFalse()
         elif isinstance(lit, BelowMin):
             if isinstance(self, (GreaterThan, GreaterThanOrEqual, NotEqualTo)):
-                return AlwaysTrue()  # type: ignore
+                return AlwaysTrue()
             elif isinstance(self, (LessThan, LessThanOrEqual, EqualTo)):
-                return AlwaysFalse()  # type: ignore
+                return AlwaysFalse()
 
         return self.as_bound(bound_term, lit)
 

tests/expressions/test_expressions.py

@@ -738,6 +738,7 @@ def test_not() -> None:
 
 def test_always_true() -> None:
     always_true = AlwaysTrue()
+    assert always_true.model_dump_json() == '"true"'
     assert str(always_true) == "AlwaysTrue()"
     assert repr(always_true) == "AlwaysTrue()"
     assert always_true == eval(repr(always_true))
@@ -746,6 +747,7 @@ def test_always_true() -> None:
 
 def test_always_false() -> None:
     always_false = AlwaysFalse()
+    assert always_false.model_dump_json() == '"false"'
     assert str(always_false) == "AlwaysFalse()"
     assert repr(always_false) == "AlwaysFalse()"
     assert always_false == eval(repr(always_false))