Rename schema to database in PostgresHook

[feluelle]

In PostgresHook the "schema" field is only being called like that to make it compatible with the underlying DbApiHook which uses the schema for the sql alchemy connector. The postgres connector library however does not allow setting a schema in the connection instead a database can be set. To clarify that, we change all references in the PostgresHook code and documentation.

related: #26734

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[feluelle]

Added 1da4ee7

To clarify, the tests were testing code which is not meant to be true for every DbApiHook as it does not set the self.schema. There is even a note already in the init covering this:

# We should not make schema available in deriving hooks for backwards compatibility
# If a hook deriving from DBApiHook has a need to access schema, then it should retrieve it
# from kwargs and store it on its own. We do not run "pop" here as we want to give the
# Hook deriving from the DBApiHook to still have access to the field in it's constructor
self.__schema = schema

[feluelle]

Thanks @jedcunningham, I will also fix the other issues.

[kaxil]

Thought: Should we add schema as property and raise deprecation warning for folks relying on PostgresHook().schema? Or we rather give them AttributeError as it is wrong anyways?

[feluelle]

I don't have a strong opinion on this. @ashb @potiuk maybe?

[ashb]

I don't think we can even make it deprecated really:

This is in DbAPIHook:

    def get_conn(self):
        """Returns a connection object"""
        db = self.get_connection(getattr(self, self.conn_name_attr))
        return self.connector.connect(host=db.host, port=db.port, username=db.login, schema=db.schema)

So we need to add a

    @property
    def schema(self):
        return self.schema

I think. I can't see how we can do that without breaking anything which uses dbapi hook, such as SQLTableCheckOperator

[feluelle]

db.schema there refers to the connection schema - not the hook schema attribute.

[ashb]

Oh right yes.

In which case I think it's still worth having a deprecation warning property.

[feluelle]

Okay, will add it.

[feluelle]

Added in 4a7ae31

[potiuk]

Conflicts need fixing :(

[feluelle]

@potiuk Done. 😊