On Tue, Jan 21, 2020, at 6:39 AM, Andrei Pashkin wrote:
> Let's suppose I have a compiled SA expression statement which I want to cache
> to avoid repetitive compilation. Let's also suppose that I can't use
> "literal_binds" because I want to provide parameter values late, after
> getting the compiled query from the cache.
>
> Is it somehow possible to inject values into compiled query without executing
> it?
>
> Here is a full example:
> https://gist.github.com/AndreiPashkin/9b497233e2a7668d0da67dc74d169812
When you execute a compiled statement using Core there is always a dictionary
of parameters you pass along. Whatever parameters you put here take precedence.
in your example you're using bindparam() directly, so this is the easiest case,
just pass "id":
def my_cached_thing():
cache = {}
stmt = sa.select([User.__table__]).where(User.__table__.c.id ==
sa.bindparam('id'))
def go(engine, id):
with engine.connect() as conn:
return conn.execution_options(compiled_cache=cache).execute(stmt, id=id)
return go
# in your code
cached_lookup = my_cached_thing()
for id in [1, 10, 15, 27, 19, 38]:
result = cached_lookup(engine, id) # will only compile the statement once
# ... etc
The above thing I did with the nested function etc. is arbitrary, just the main
point is, same statement object and same cache dictionary. as stated before,
1.4 will hopefully have an improvement to make all of this transparent.
Also note you can use Core select() constructs etc with the ORM classes
directly:
select([User]).where(User.id == bindparam('id'))
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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SQLAlchemy -
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http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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