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# dialects/mssql/json.py
# Copyright (C) 2005-2024 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://www.opensource.org/licenses/mit-license.php
# mypy: ignore-errors
from ... import types as sqltypes
# technically, all the dialect-specific datatypes that don't have any special
# behaviors would be private with names like _MSJson. However, we haven't been
# doing this for mysql.JSON or sqlite.JSON which both have JSON / JSONIndexType
# / JSONPathType in their json.py files, so keep consistent with that
# sub-convention for now. A future change can update them all to be
# package-private at once.
class JSON(sqltypes.JSON):
"""MSSQL JSON type.
MSSQL supports JSON-formatted data as of SQL Server 2016.
The :class:`_mssql.JSON` datatype at the DDL level will represent the
datatype as ``NVARCHAR(max)``, but provides for JSON-level comparison
functions as well as Python coercion behavior.
:class:`_mssql.JSON` is used automatically whenever the base
:class:`_types.JSON` datatype is used against a SQL Server backend.
.. seealso::
:class:`_types.JSON` - main documentation for the generic
cross-platform JSON datatype.
The :class:`_mssql.JSON` type supports persistence of JSON values
as well as the core index operations provided by :class:`_types.JSON`
datatype, by adapting the operations to render the ``JSON_VALUE``
or ``JSON_QUERY`` functions at the database level.
The SQL Server :class:`_mssql.JSON` type necessarily makes use of the
``JSON_QUERY`` and ``JSON_VALUE`` functions when querying for elements
of a JSON object. These two functions have a major restriction in that
they are **mutually exclusive** based on the type of object to be returned.
The ``JSON_QUERY`` function **only** returns a JSON dictionary or list,
but not an individual string, numeric, or boolean element; the
``JSON_VALUE`` function **only** returns an individual string, numeric,
or boolean element. **both functions either return NULL or raise
an error if they are not used against the correct expected value**.
To handle this awkward requirement, indexed access rules are as follows:
1. When extracting a sub element from a JSON that is itself a JSON
dictionary or list, the :meth:`_types.JSON.Comparator.as_json` accessor
should be used::
stmt = select(
data_table.c.data["some key"].as_json()
).where(
data_table.c.data["some key"].as_json() == {"sub": "structure"}
)
2. When extracting a sub element from a JSON that is a plain boolean,
string, integer, or float, use the appropriate method among
:meth:`_types.JSON.Comparator.as_boolean`,
:meth:`_types.JSON.Comparator.as_string`,
:meth:`_types.JSON.Comparator.as_integer`,
:meth:`_types.JSON.Comparator.as_float`::
stmt = select(
data_table.c.data["some key"].as_string()
).where(
data_table.c.data["some key"].as_string() == "some string"
)
.. versionadded:: 1.4
"""
# note there was a result processor here that was looking for "number",
# but none of the tests seem to exercise it.
# Note: these objects currently match exactly those of MySQL, however since
# these are not generalizable to all JSON implementations, remain separately
# implemented for each dialect.
class _FormatTypeMixin:
def _format_value(self, value):
raise NotImplementedError()
def bind_processor(self, dialect):
super_proc = self.string_bind_processor(dialect)
def process(value):
value = self._format_value(value)
if super_proc:
value = super_proc(value)
return value
return process
def literal_processor(self, dialect):
super_proc = self.string_literal_processor(dialect)
def process(value):
value = self._format_value(value)
if super_proc:
value = super_proc(value)
return value
return process
class JSONIndexType(_FormatTypeMixin, sqltypes.JSON.JSONIndexType):
def _format_value(self, value):
if isinstance(value, int):
value = "$[%s]" % value
else:
value = '$."%s"' % value
return value
class JSONPathType(_FormatTypeMixin, sqltypes.JSON.JSONPathType):
def _format_value(self, value):
return "$%s" % (
"".join(
[
"[%s]" % elem if isinstance(elem, int) else '."%s"' % elem
for elem in value
]
)
)