Define json functions for old SQLite versions

beets/dbcore/db.py

@@ -27,10 +27,11 @@ import time
 from abc import ABC
 from collections import defaultdict
 from collections.abc import Generator, Iterable, Iterator, Mapping, Sequence
-from sqlite3 import Connection
+from sqlite3 import Connection, sqlite_version
 from typing import TYPE_CHECKING, Any, AnyStr, Callable, Generic, TypeVar, cast
 
 from mediafile import MediaFile
+from packaging.version import Version
 from rich import print
 from rich_tables.generic import flexitable
 from unidecode import unidecode
@@ -1128,9 +1129,71 @@ class Database:
 
             return bytestring
 
+        def json_patch(first: str, second: str) -> str:
+            """Implementation of the 'json_patch' SQL function.
+
+            This function merges two JSON strings together.
+            """
+            first_dict = json.loads(first)
+            second_dict = json.loads(second)
+            first_dict.update(second_dict)
+            return json.dumps(first_dict)
+
+        def json_extract(json_str: str, key: str) -> str | None:
+            """Simple implementation of the 'json_extract' SQLite function.
+
+            The original implementation in SQLite allows traversing objects of
+            any depth. Here, we only ever deal with a flat dictionary, thus
+            we can simplify the implementation to a single 'get' call.
+            """
+            if json_str:
+                return json.loads(json_str).get(key.replace("$.", ""))
+
+            return None
+
+        class JSONGroupObject:
+            """Implementation of the 'json_group_object' SQLite aggregate.
+
+            An aggregate function which accepts two values (key, val) and
+            groups all {key: val} pairs into a single object.
+
+            It is found in the json1 extension which is included in SQLite
+            by default since version 3.38.0 (2022-02-22). To ensure support
+            for older SQLite versions, we add our implementation.
+
+            Notably, it does not exist on Windows in Python 3.8.
+
+            Consider the following table
+
+            id  key    val
+            1   plays  "10"
+            1   skips  "20"
+            2   city   "London"
+
+            SELECT id, group_to_json(key, val) GROUP BY id
+                1, '{"plays": "10", "skips": "20"}'
+                2, '{"city": "London"}'
+            """
+
+            def __init__(self) -> None:
+                self.flex: dict[str, SQLiteType] = {}
+
+            def step(self, field: str, value: SQLiteType) -> None:
+                if field:
+                    self.flex[field] = value
+
+            def finalize(self) -> str:
+                return json.dumps(self.flex)
+
         conn.create_function("regexp", 2, regexp)
         conn.create_function("unidecode", 1, unidecode)
         conn.create_function("bytelower", 1, bytelower)
+        if Version(sqlite_version) < Version("3.38.0"):
+            # create 'json_group_object' for older SQLite versions that do
+            # not include the json1 extension by default
+            conn.create_aggregate("json_group_object", 2, JSONGroupObject)
+            conn.create_function("json_patch", 2, json_patch)
+            conn.create_function("json_extract", 2, json_extract)
 
     def _close(self):
         """Close the all connections to the underlying SQLite database