default schema / schema translation map as an execution argument

[Mike Bayer]

this comes up a lot, the need to swap in a schema name for all tables. this is an easy add as an execution option, most of a patch is attached, needs tests.

[Mike Bayer]

the usage pattern would be like:

conn = connection.execution_options(default_schema="foo")
conn.execute(stmt)

to generate the SQL plain looks like:

from sqlalchemy import *
from sqlalchemy import schema

m = MetaData()
t1 = Table('t1', m, Column('x', Integer))

print t1.select().compile()
print t1.select().compile(compile_kwargs={'default_schema': 'foo'})

print schema.CreateTable(t1).compile(compile_kwargs={'default_schema': 'foo'})

[Mike Bayer]

this patch works for rendering but isn't taken into account by the inspector. needs that also.

[Mike Bayer]

we might want to look into providing a "swap" feature, e.g. if an app has tables in "(default)", "schema_a", "schema_b", a lookup table can be sent in such that any of these three can be exchanged for another.

[Mike Bayer]

wip at b243f5b340b9a0bee4f2bd4e50398f9cfa1ab6bd

[Mike Bayer]

• Multi-tenancy schema translation for :class:.Table objects is added. This supports the use case of an application that uses the same set of :class:.Table objects in many schemas, such as schema-per-user. A new execution option :paramref:.Connection.execution_options.schema_translate_map is added. fixes #2685
• latest tox doesn't like the {posargs} in the profile rerunner

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