feat(firestore): new generic pipeline expressions

packages/google-cloud-firestore/google/cloud/firestore_v1/pipeline_expressions.py

@@ -188,7 +188,7 @@ class Expression(ABC):
     """Represents an expression that can be evaluated to a value within the
     execution of a pipeline.
 
-    Expressionessions are the building blocks for creating complex queries and
+    Expressions are the building blocks for creating complex queries and
     transformations in Firestore pipelines. They can represent:
 
     - **Field references:** Access values from document fields.
@@ -761,6 +761,9 @@ def array_get(self, offset: Expression | int) -> "FunctionExpression":
         Creates an expression that indexes into an array from the beginning or end and returns the
         element. A negative offset starts from the end.
 
+        If the expression is evaluated against a non-array type, it evaluates to an error. See `offset`
+        for an alternative that evaluates to unset instead.
+
         Example:
             >>> Array([1,2,3]).array_get(0)
 
@@ -774,6 +777,26 @@ def array_get(self, offset: Expression | int) -> "FunctionExpression":
             "array_get", [self, self._cast_to_expr_or_convert_to_constant(offset)]
         )
 
+    @expose_as_static
+    def offset(self, offset: Expression | int) -> "FunctionExpression":
+        """
+        Creates an expression that indexes into an array from the beginning or end and returns the
+        element. A negative offset starts from the end.
+        If the expression is evaluated against a non-array type, it evaluates to unset.
+
+        Example:
+            >>> Array([1,2,3]).offset(0)
+
+        Args:
+            offset: the index of the element to return
+
+        Returns:
+            A new `Expression` representing the `offset` operation.
+        """
+        return FunctionExpression(
+            "offset", [self, self._cast_to_expr_or_convert_to_constant(offset)]
+        )
+
     @expose_as_static
     def array_contains(
         self, element: Expression | CONSTANT_TYPE
@@ -877,6 +900,70 @@ def array_reverse(self) -> "Expression":
         """
         return FunctionExpression("array_reverse", [self])
 
+    @expose_as_static
+    def array_filter(
+        self,
+        filter_expr: "BooleanExpression",
+        element_alias: str | Constant[str],
+        index_alias: str | Constant[str] | None = None,
+    ) -> "Expression":
+        """Filters an array based on a predicate.
+
+        Example:
+            >>> # Filter the 'tags' array to only include the tag "comedy"
+            >>> Field.of("tags").array_filter(Variable("tag").equal("comedy"), "tag")
+            >>> # Filter the 'tags' array to only include elements after the first element (index > 0)
+            >>> Field.of("tags").array_filter(Variable("i").greater_than(0), element_alias="tag", index_alias="i")
+
+        Args:
+            filter_expr: The predicate boolean expression used to filter the elements.
+            element_alias: A string or string constant used to refer to the current array
+                element as a variable within the filter expression.
+            index_alias: An optional string or string constant used to refer to the index
+                of the current array element as a variable within the filter expression.
+
+        Returns:
+            A new `Expression` representing the filtered array.
+        """
+        args = [self, self._cast_to_expr_or_convert_to_constant(element_alias)]
+        if index_alias is not None:
+            args.append(self._cast_to_expr_or_convert_to_constant(index_alias))
+        args.append(filter_expr)
+
+        return FunctionExpression("array_filter", args)
+
+    @expose_as_static
+    def array_transform(
+        self,
+        transform_expr: "Expression",
+        element_alias: str | Constant[str],
+        index_alias: str | Constant[str] | None = None,
+    ) -> "Expression":
+        """Creates an expression that applies a provided transformation to each element in an array.
+
+        Example:
+            >>> # Convert each tag in the 'tags' array to uppercase
+            >>> Field.of("tags").array_transform(Variable("tag").to_upper(), "tag")
+            >>> # Append the index to each tag in the 'tags' array
+            >>> Field.of("tags").array_transform(Variable("tag").string_concat(Variable("i")), element_alias="tag", index_alias="i")
+
+        Args:
+            transform_expr: The expression used to transform the elements.
+            element_alias: A string or string constant used to refer to the current array
+                element as a variable within the transform expression.
+            index_alias: An optional string or string constant used to refer to the index
+                of the current array element as a variable within the transform expression.
+
+        Returns:
+            A new `Expression` representing the transformed array.
+        """
+        args = [self, self._cast_to_expr_or_convert_to_constant(element_alias)]
+        if index_alias is not None:
+            args.append(self._cast_to_expr_or_convert_to_constant(index_alias))
+        args.append(transform_expr)
+
+        return FunctionExpression("array_transform", args)
+
     @expose_as_static
     def array_concat(
         self, *other_arrays: Array | list[Expression | CONSTANT_TYPE] | Expression
@@ -938,7 +1025,7 @@ def is_absent(self) -> "BooleanExpression":
             >>> Field.of("email").is_absent()
 
         Returns:
-            A new `BooleanExpressionession` representing the isAbsent operation.
+            A new `BooleanExpression` representing the isAbsent operation.
         """
         return BooleanExpression("is_absent", [self])
 
@@ -1006,6 +1093,76 @@ def exists(self) -> "BooleanExpression":
         """
         return BooleanExpression("exists", [self])
 
+    @expose_as_static
+    def coalesce(self, *others: Expression | CONSTANT_TYPE) -> "Expression":
+        """Creates an expression that evaluates to the first non-null, non-error value.
+
+        Example:
+            >>> # Return the "preferredName" field if it exists.
+            >>> # Otherwise, check the "fullName" field.
+            >>> # Otherwise, return the literal string "Anonymous".
+            >>> Field.of("preferredName").coalesce(Field.of("fullName"), "Anonymous")
+
+            >>> # Equivalent static call:
+            >>> Expression.coalesce(Field.of("preferredName"), Field.of("fullName"), "Anonymous")
+
+        Args:
+            *others: Additional expressions or constants to evaluate if the current
+                expression evaluates to null or error.
+
+        Returns:
+            An Expression representing the coalesce operation.
+        """
+        return FunctionExpression(
+            "coalesce",
+            [self]
+            + [Expression._cast_to_expr_or_convert_to_constant(x) for x in others],
+        )
+
+    @expose_as_static
+    def switch_on(
+        self, result: Expression | CONSTANT_TYPE, *others: Expression | CONSTANT_TYPE
+    ) -> "Expression":
+        """Creates an expression that evaluates to the result corresponding to the first true condition.
+
+        This function behaves like a `switch` statement. It accepts an alternating sequence of
+        conditions and their corresponding results. If an odd number of arguments is provided, the
+        final argument serves as a default fallback result. If no default is provided and no condition
+        evaluates to true, it throws an error.
+
+        Example:
+            >>> # Return "Pending" if status is 1, "Active" if status is 2, otherwise "Unknown"
+            >>> Field.of("status").equal(1).switch_on(
+            ...     "Pending", Field.of("status").equal(2), "Active", "Unknown"
+            ... )
+
+        Args:
+            result: The result to return if this condition is true.
+            *others: Additional alternating conditions and results, optionally followed by a default value.
+
+        Returns:
+            An Expression representing the "switch_on" operation.
+        """
+        return FunctionExpression(
+            "switch_on",
+            [self, Expression._cast_to_expr_or_convert_to_constant(result)]
+            + [Expression._cast_to_expr_or_convert_to_constant(x) for x in others],
+        )
+
+    @expose_as_static
+    def storage_size(self) -> "Expression":
+        """Calculates the Firestore storage size of a given value.
+
+        Mirrors the sizing rules detailed in Firebase/Firestore documentation.
+
+        Example:
+            >>> Field.of("content").storage_size()
+
+        Returns:
+            A new `Expression` representing the storage size.
+        """
+        return FunctionExpression("storage_size", [self])
+
     @expose_as_static
     def sum(self) -> "Expression":
         """Creates an aggregation that calculates the sum of a numeric field across multiple stage inputs.
@@ -1366,6 +1523,7 @@ def join(self, delimeter: Expression | str) -> "Expression":
     @expose_as_static
     def map_get(self, key: str | Constant[str]) -> "Expression":
         """Accesses a value from the map produced by evaluating this expression.
+        If the expression is evaluated against a non-map type, it evaluates to an error.
 
         Example:
             >>> Map({"city": "London"}).map_get("city")
@@ -2808,6 +2966,22 @@ def __init__(self, *conditions: "BooleanExpression"):
         super().__init__("or", conditions, use_infix_repr=False)
 
 
+class Nor(BooleanExpression):
+    """
+    Represents an expression that performs a logical 'NOR' operation on multiple filter conditions.
+
+    Example:
+        >>> # Check if neither the 'age' field is greater than 18 nor the 'city' field is "London"
+        >>> Nor(Field.of("age").greater_than(18), Field.of("city").equal("London"))
+
+    Args:
+        *conditions: The filter conditions to 'NOR' together.
+    """
+
+    def __init__(self, *conditions: "BooleanExpression"):
+        super().__init__("nor", conditions, use_infix_repr=False)
+
+
 class Xor(BooleanExpression):
     """
     Represents an expression that performs a logical 'XOR' (exclusive OR) operation on multiple filter conditions.