JSON keys order

[yoch....@gmail.com]

Hi,

I have a problem with a custom JSON type, which is not preserving keys order, despite that I'm using python 3.8.

Here is the type definition and usage:

```

import json

from sqlalchemy import Column, Integer

from sqlalchemy.types import TypeDecorator, TEXT

from sqlalchemy.ext.mutable import MutableDict

class JSONType(TypeDecorator):

    impl = TEXT

    def process_bind_param(self, value, dialect):

        if value is not None:

            value = json.dumps(value)

        return value

    def process_result_value(self, value, dialect):

        if value is not None:

            value = json.loads(value)

        return value

JSONDict = MutableDict.as_mutable(JSONType)

Base = automap_base()

class Picture(Base):

    __tablename__ = 'picture'

    id = Column(Integer, primary_key=True)

    data = Column(JSONDict)

```

When I'm storing values in the data field (values are nested elements of different types), store the picture in database and reload it, the keys order of data dict is not preserved. I'm don't understand why, because the version of python I'm using is supposed to keep the dict insertion order.

Have you some idea how to solve that ? The JSON keys order is important for my application.

Thank you

[Mike Bayer]

perhaps Python's json encoder does not maintain ordering?   I don't know either.   Can you set echo='debug' on your create_engine() and examine the parameters being passed as well as the data being returned?   also I'm not seeing which database backend or driver you're using which may be significant (particularly if its PostgreSQL which has a fully native JSON datatype).

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[yoch....@gmail.com]

Thank you for your answer.

I'm using MySQL 8 with pymysql.

The `data` column has JSON type, and it seems that MySQL is actually reordering keys.

[Mike Bayer]

thanks, indeed mysql 8 reorders the keys

https://stackoverflow.com/a/48382771

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