I'm using SQLAlchemy Core. A user prepares an "on" expression for a join query
and passes it to a function. The goal of the function is to hide some messy
details the must be done to perform the join. Part of these details include
doing a subselect. So in the implentation, the subselect is turned into an
alias, but now the on clause that was passed in no longer references the proper
table. I'd like to know how to transform an expression so that all references
to tableA are replaced with alias name tableB.
Pseudocode:
cols = [... in terms of tableA and tableB]
onclause = tableA.c.colX == tableB.c.colX
alias = sqla.select(cols).alias('hi')
updated_onclause = magic(onclause, tableA, alias)
So I need magic() to return an expression equal to:
alias.c.colX == tableB.c.colX
My hack it to manipulate the generated sql and then use sqla.text(), which is
certainly not ideal.
So how can I manipulate an arbitrary expression (intended for use as a join
clause or where clause), replacing all appearances of a table with an alias of
that same table?
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