feat(duckdb): add to_json() to Table and duckdb backend

Fixes #10413

Author: NickCrews

ibis/backends/__init__.py

@@ -586,6 +586,32 @@ def to_delta(
         with expr.to_pyarrow_batches(params=params) as batch_reader:
             write_deltalake(path, batch_reader, **kwargs)
 
+    @util.experimental
+    def to_json(
+        self,
+        expr: ir.Table,
+        path: str | Path,
+        **kwargs: Any,
+    ) -> None:
+        """Write the results of `expr` to a json file of [{column -> value}, ...] objects.
+
+        This method is eager and will execute the associated expression
+        immediately.
+
+        Parameters
+        ----------
+        expr
+            The ibis expression to execute and persist to Delta Lake table.
+        path
+            The data source. A string or Path to the Delta Lake table.
+        kwargs
+            Additional, backend-specifc keyword arguments.
+        """
+        backend = expr._find_backend(use_default=True)
+        raise NotImplementedError(
+            f"{backend.__class__.__name__} does not support writing to JSON."
+        )
+
 
 class CanListCatalog(abc.ABC):
     @abc.abstractmethod

ibis/backends/duckdb/__init__.py

@@ -8,7 +8,7 @@
 import warnings
 from operator import itemgetter
 from pathlib import Path
-from typing import TYPE_CHECKING, Any
+from typing import TYPE_CHECKING, Any, Literal
 
 import duckdb
 import pyarrow as pa
@@ -1566,6 +1566,45 @@ def to_geo(
         with self._safe_raw_sql(copy_cmd):
             pass
 
+    @util.experimental
+    def to_json(
+        self,
+        expr: ir.Table,
+        path: str | Path,
+        *,
+        compression: Literal["auto", "none", "gzip", "zstd"] = "auto",
+        dateformat: str | None = None,
+        timestampformat: str | None = None,
+    ) -> None:
+        """Write the results of `expr` to a json file of [{column -> value}, ...] objects.
+
+        This method is eager and will execute the associated expression
+        immediately.
+        See https://duckdb.org/docs/sql/statements/copy.html#json-options
+        for more info.
+
+        Parameters
+        ----------
+        expr
+            The ibis expression to execute and persist to Delta Lake table.
+        path
+            URLs such as S3 buckets are supported.
+        compression
+            Compression codec to use. One of "auto", "none", "gzip", "zstd".
+        dateformat
+            Date format string.
+        timestampformat
+            Timestamp format string.
+        """
+        opts = f", COMPRESSION '{compression.upper()}'"
+        if dateformat:
+            opts += f", DATEFORMAT '{dateformat}'"
+        if timestampformat:
+            opts += f", TIMESTAMPFORMAT '{timestampformat}'"
+        self.raw_sql(
+            f"COPY ({self.compile(expr)}) TO '{path!s}' (FORMAT JSON, ARRAY true{opts});"
+        )
+
     def _get_schema_using_query(self, query: str) -> sch.Schema:
         with self._safe_raw_sql(f"DESCRIBE {query}") as cur:
             rows = cur.fetch_arrow_table()

ibis/backends/tests/test_export.py

@@ -347,6 +347,38 @@ def test_table_to_csv(tmp_path, backend, awards_players):
     backend.assert_frame_equal(awards_players.to_pandas(), df)
 
 
+@pytest.mark.notimpl(
+    [
+        "athena",
+        "bigquery",
+        "clickhouse",
+        "databricks",
+        "datafusion",
+        "druid",
+        "exasol",
+        "flink",
+        "impala",
+        "mssql",
+        "mysql",
+        "oracle",
+        "polars",
+        "postgres",
+        "pyspark",
+        "risingwave",
+        "snowflake",
+        "sqlite",
+        "trino",
+    ],
+    reason="haven't gotten to them yet. Might be easy!",
+    raises=NotImplementedError,
+)
+def test_to_json(backend, tmp_path, awards_players):
+    out_path = tmp_path / "out.json"
+    awards_players.to_json(out_path)
+    df = pd.read_json(out_path, orient="records")
+    backend.assert_frame_equal(awards_players.to_pandas(), df)
+
+
 @pytest.mark.notimpl(
     ["duckdb"],
     reason="cannot inline WriteOptions objects",

ibis/expr/types/core.py

@@ -771,6 +771,28 @@ def to_delta(
         """
         self._find_backend(use_default=True).to_delta(self, path, **kwargs)
 
+    @experimental
+    def to_json(
+        self,
+        path: str | Path,
+        **kwargs: Any,
+    ) -> None:
+        """Write the results of `expr` to a json file of [{column -> value}, ...] objects.
+
+        This method is eager and will execute the associated expression
+        immediately.
+
+        Parameters
+        ----------
+        expr
+            The ibis expression to execute and persist to Delta Lake table.
+        path
+            The data source. A string or Path to the Delta Lake table.
+        kwargs
+            Additional, backend-specifc keyword arguments.
+        """
+        self._find_backend(use_default=True).to_json(self, path, **kwargs)
+
     @experimental
     def to_torch(
         self,