datafusion_physical_expr/expressions/
literal.rs

1// Licensed to the Apache Software Foundation (ASF) under one
2// or more contributor license agreements.  See the NOTICE file
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4// regarding copyright ownership.  The ASF licenses this file
5// to you under the Apache License, Version 2.0 (the
6// "License"); you may not use this file except in compliance
7// with the License.  You may obtain a copy of the License at
8//
9//   http://www.apache.org/licenses/LICENSE-2.0
10//
11// Unless required by applicable law or agreed to in writing,
12// software distributed under the License is distributed on an
13// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17
18//! Literal expressions for physical operations
19
20use std::hash::Hash;
21use std::sync::Arc;
22
23use crate::physical_expr::PhysicalExpr;
24
25use arrow::datatypes::{Field, FieldRef};
26use arrow::{
27    datatypes::{DataType, Schema},
28    record_batch::RecordBatch,
29};
30use datafusion_common::metadata::FieldMetadata;
31use datafusion_common::{Result, ScalarValue};
32use datafusion_expr::Expr;
33use datafusion_expr_common::columnar_value::ColumnarValue;
34use datafusion_expr_common::interval_arithmetic::Interval;
35use datafusion_expr_common::placement::ExpressionPlacement;
36use datafusion_expr_common::sort_properties::{ExprProperties, SortProperties};
37
38/// Represents a literal value
39#[derive(Debug, PartialEq, Eq, Clone)]
40pub struct Literal {
41    value: ScalarValue,
42    field: FieldRef,
43}
44
45impl Hash for Literal {
46    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
47        self.value.hash(state);
48        let metadata = self.field.metadata();
49        let mut keys = metadata.keys().collect::<Vec<_>>();
50        keys.sort();
51        for key in keys {
52            key.hash(state);
53            metadata.get(key).unwrap().hash(state);
54        }
55    }
56}
57
58impl Literal {
59    /// Create a literal value expression
60    pub fn new(value: ScalarValue) -> Self {
61        Self::new_with_metadata(value, None)
62    }
63
64    /// Create a literal value expression
65    pub fn new_with_metadata(
66        value: ScalarValue,
67        metadata: Option<FieldMetadata>,
68    ) -> Self {
69        let mut field = Field::new("lit".to_string(), value.data_type(), value.is_null());
70
71        if let Some(metadata) = metadata {
72            field = metadata.add_to_field(field);
73        }
74
75        Self {
76            value,
77            field: field.into(),
78        }
79    }
80
81    /// Get the scalar value
82    pub fn value(&self) -> &ScalarValue {
83        &self.value
84    }
85}
86
87impl std::fmt::Display for Literal {
88    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
89        write!(f, "{}", self.value)
90    }
91}
92
93impl PhysicalExpr for Literal {
94    fn data_type(&self, _input_schema: &Schema) -> Result<DataType> {
95        Ok(self.value.data_type())
96    }
97
98    fn nullable(&self, _input_schema: &Schema) -> Result<bool> {
99        Ok(self.value.is_null())
100    }
101
102    fn return_field(&self, _input_schema: &Schema) -> Result<FieldRef> {
103        Ok(Arc::clone(&self.field))
104    }
105
106    fn evaluate(&self, _batch: &RecordBatch) -> Result<ColumnarValue> {
107        Ok(ColumnarValue::Scalar(self.value.clone()))
108    }
109
110    fn children(&self) -> Vec<&Arc<dyn PhysicalExpr>> {
111        vec![]
112    }
113
114    fn with_new_children(
115        self: Arc<Self>,
116        _children: Vec<Arc<dyn PhysicalExpr>>,
117    ) -> Result<Arc<dyn PhysicalExpr>> {
118        Ok(self)
119    }
120
121    fn get_properties(&self, _children: &[ExprProperties]) -> Result<ExprProperties> {
122        Ok(ExprProperties {
123            sort_properties: SortProperties::Singleton,
124            range: Interval::try_new(self.value().clone(), self.value().clone())?,
125            preserves_lex_ordering: true,
126            // Vacuously true: a literal has no ordered inputs.
127            strictly_order_preserving: true,
128        })
129    }
130
131    fn fmt_sql(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
132        std::fmt::Display::fmt(self, f)
133    }
134
135    fn placement(&self) -> ExpressionPlacement {
136        ExpressionPlacement::Literal
137    }
138
139    #[cfg(feature = "proto")]
140    fn try_to_proto(
141        &self,
142        _ctx: &datafusion_physical_expr_common::physical_expr::proto_encode::PhysicalExprEncodeCtx<'_>,
143    ) -> Result<Option<datafusion_proto_models::protobuf::PhysicalExprNode>> {
144        use datafusion_proto_models::protobuf;
145
146        Ok(Some(protobuf::PhysicalExprNode {
147            expr_id: None,
148            expr_type: Some(protobuf::physical_expr_node::ExprType::Literal(
149                (&self.value).try_into()?,
150            )),
151        }))
152    }
153}
154
155#[cfg(feature = "proto")]
156impl Literal {
157    /// Reconstruct a [`Literal`] from its protobuf representation.
158    pub fn try_from_proto(
159        node: &datafusion_proto_models::protobuf::PhysicalExprNode,
160        _ctx: &datafusion_physical_expr_common::physical_expr::proto_decode::PhysicalExprDecodeCtx<'_>,
161    ) -> Result<Arc<dyn PhysicalExpr>> {
162        use datafusion_physical_expr_common::expect_expr_variant;
163        use datafusion_proto_models::protobuf;
164
165        let scalar_proto = expect_expr_variant!(
166            node,
167            protobuf::physical_expr_node::ExprType::Literal,
168            "Literal",
169        );
170        let value = ScalarValue::try_from(scalar_proto)?;
171        Ok(Arc::new(Literal::new(value)))
172    }
173}
174
175/// Create a literal expression
176#[expect(clippy::needless_pass_by_value)]
177pub fn lit<T: datafusion_expr::Literal>(value: T) -> Arc<dyn PhysicalExpr> {
178    match value.lit() {
179        Expr::Literal(v, _) => Arc::new(Literal::new(v)),
180        _ => unreachable!(),
181    }
182}
183
184#[cfg(test)]
185mod tests {
186    use super::*;
187
188    use arrow::array::Int32Array;
189    use datafusion_common::cast::as_int32_array;
190    use datafusion_physical_expr_common::physical_expr::fmt_sql;
191
192    #[test]
193    fn literal_i32() -> Result<()> {
194        // create an arbitrary record batch
195        let schema = Schema::new(vec![Field::new("a", DataType::Int32, true)]);
196        let a = Int32Array::from(vec![Some(1), None, Some(3), Some(4), Some(5)]);
197        let batch = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(a)])?;
198
199        // create and evaluate a literal expression
200        let literal_expr = lit(42i32);
201        assert_eq!("42", format!("{literal_expr}"));
202
203        let literal_array = literal_expr
204            .evaluate(&batch)?
205            .into_array(batch.num_rows())
206            .expect("Failed to convert to array");
207        let literal_array = as_int32_array(&literal_array)?;
208
209        // note that the contents of the literal array are unrelated to the batch contents except for the length of the array
210        assert_eq!(literal_array.len(), 5); // 5 rows in the batch
211        for i in 0..literal_array.len() {
212            assert_eq!(literal_array.value(i), 42);
213        }
214
215        Ok(())
216    }
217
218    #[test]
219    fn test_fmt_sql() -> Result<()> {
220        // create and evaluate a literal expression
221        let expr = lit(42i32);
222        let display_string = expr.to_string();
223        assert_eq!(display_string, "42");
224        let sql_string = fmt_sql(expr.as_ref()).to_string();
225        assert_eq!(sql_string, "42");
226
227        Ok(())
228    }
229}
230
231/// Tests for the `try_to_proto` / `try_from_proto` hooks.
232#[cfg(all(test, feature = "proto"))]
233mod proto_tests {
234    use super::*;
235    use crate::proto_test_util::{StubEncoder, UnreachableDecoder, column_node};
236    use datafusion_common::DataFusionError;
237    use datafusion_physical_expr_common::physical_expr::proto_decode::PhysicalExprDecodeCtx;
238    use datafusion_physical_expr_common::physical_expr::proto_encode::PhysicalExprEncodeCtx;
239    use datafusion_proto_models::protobuf::physical_expr_node;
240
241    fn i32_literal() -> Literal {
242        Literal::new(ScalarValue::Int32(Some(42)))
243    }
244
245    // ── try_to_proto ─────────────────────────────────────────────────────────
246
247    #[test]
248    fn try_to_proto_encodes_literal() {
249        let literal = i32_literal();
250        let encoder = StubEncoder::ok();
251        let ctx = PhysicalExprEncodeCtx::new(&encoder);
252
253        let node = literal
254            .try_to_proto(&ctx)
255            .unwrap()
256            .expect("Literal should encode to Some(node)");
257
258        // Literal nodes never set expr_id.
259        assert!(node.expr_id.is_none());
260        // Variant must be Literal, not any other expr type.
261        assert!(matches!(
262            node.expr_type,
263            Some(physical_expr_node::ExprType::Literal(_))
264        ));
265    }
266
267    #[test]
268    fn try_to_proto_null_literal() {
269        let literal = Literal::new(ScalarValue::Int32(None));
270        let encoder = StubEncoder::ok();
271        let ctx = PhysicalExprEncodeCtx::new(&encoder);
272
273        let node = literal
274            .try_to_proto(&ctx)
275            .unwrap()
276            .expect("null Literal should encode to Some(node)");
277
278        assert!(matches!(
279            node.expr_type,
280            Some(physical_expr_node::ExprType::Literal(_))
281        ));
282
283        // Decode and verify the null payload round-trips correctly.
284        let schema = Schema::empty();
285        let decoder = UnreachableDecoder;
286        let dec_ctx = PhysicalExprDecodeCtx::new(&schema, &decoder);
287        let decoded = Literal::try_from_proto(&node, &dec_ctx).unwrap();
288        let lit = decoded
289            .downcast_ref::<Literal>()
290            .expect("decoded expr should be a Literal");
291        assert_eq!(lit.value(), &ScalarValue::Int32(None));
292    }
293
294    // ── try_from_proto ───────────────────────────────────────────────────────
295
296    #[test]
297    fn try_from_proto_roundtrip() {
298        let original = i32_literal();
299        let encoder = StubEncoder::ok();
300        let enc_ctx = PhysicalExprEncodeCtx::new(&encoder);
301
302        let node = original
303            .try_to_proto(&enc_ctx)
304            .unwrap()
305            .expect("should encode");
306
307        let schema = Schema::empty();
308        let decoder = UnreachableDecoder;
309        let dec_ctx = PhysicalExprDecodeCtx::new(&schema, &decoder);
310
311        let decoded = Literal::try_from_proto(&node, &dec_ctx).unwrap();
312        let lit = decoded
313            .downcast_ref::<Literal>()
314            .expect("decoded expr should be a Literal");
315        assert_eq!(lit.value(), &ScalarValue::Int32(Some(42)));
316    }
317
318    #[test]
319    fn try_from_proto_rejects_non_literal_node() {
320        let node = column_node("a");
321        let schema = Schema::empty();
322        let decoder = UnreachableDecoder;
323        let ctx = PhysicalExprDecodeCtx::new(&schema, &decoder);
324        let err = Literal::try_from_proto(&node, &ctx).unwrap_err();
325        assert!(
326            matches!(err, DataFusionError::Internal(ref msg) if msg.contains("PhysicalExprNode is not a Literal"))
327        );
328    }
329}
datafusion_physical_expr/expressions/literal.rs

datafusion_physical_expr/expressions/
literal.rs
