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S )� )�typesc @ s e Zd ZdZdS )�JSONa� 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
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