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How to do coalesce on aggregation? #293

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dekoza opened this Issue Sep 11, 2017 · 2 comments

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@dekoza

dekoza commented Sep 11, 2017

I want to annotate results with the last time a page was displayed and then sort in descendant order. Unfortunately when there is no such date I get None which messes the order by juping in front.
When I tried to use max(i.created) if i.created else datetime(1970,1,1) I got Expression is too complex to decompile error

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kozlovsky Sep 18, 2017

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Thank you for reporting! I agree that Pony should support coalesce function, and we just added support of it in b63634b and ccbcf8c. Starting from release 0.7.3 you will be able to write

coalesce(max(i.created), datetime(1970, 1, 1))

Regarding Expression is too complex to decompile error, that arises because at this moment Pony decompiler cannot handle if-expression bytecode. In order to use if-expressions, you need to pass generator text as a string. By the way, you query looks incorrect: if-expression should be inside max function:

max(i.created if i.created is not None else datetime(1970, 1, 1))

Also, I'm not sure the query is logically correct. When you use aggregation, you need to have some grouping, and it is not clear to me what you want to place to GROUP BY section of your SQL query

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kozlovsky commented Sep 18, 2017

Thank you for reporting! I agree that Pony should support coalesce function, and we just added support of it in b63634b and ccbcf8c. Starting from release 0.7.3 you will be able to write

coalesce(max(i.created), datetime(1970, 1, 1))

Regarding Expression is too complex to decompile error, that arises because at this moment Pony decompiler cannot handle if-expression bytecode. In order to use if-expressions, you need to pass generator text as a string. By the way, you query looks incorrect: if-expression should be inside max function:

max(i.created if i.created is not None else datetime(1970, 1, 1))

Also, I'm not sure the query is logically correct. When you use aggregation, you need to have some grouping, and it is not clear to me what you want to place to GROUP BY section of your SQL query

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dekoza Sep 18, 2017

That is awesome news! Thank you! Please disregard the second part, I was indeed using Pony in the wrong way ;)

dekoza commented Sep 18, 2017

That is awesome news! Thank you! Please disregard the second part, I was indeed using Pony in the wrong way ;)

@kozlovsky kozlovsky self-assigned this Sep 19, 2017

@kozlovsky kozlovsky added this to the 0.7.3 milestone Sep 19, 2017

@kozlovsky kozlovsky closed this Sep 19, 2017

kozlovsky added a commit that referenced this issue Oct 23, 2017

Pony ORM Release 0.7.3 (2017-10-23)
# New features

* `where()` method added to query
* `coalesce()` function added
* `between(x, a, b)` function added
* #295: Add `_table_options_` for entity class to specify engine, tablespace, etc.
* Make debug flag thread-local
* `sql_debugging` context manager added
* `sql_debug` and show_values arguments to db_session added
* `set_sql_debug` function added as alias to (to be deprecated) `sql_debug` function
* Allow `db_session` to accept `ddl` parameter when used as context manager
* Add `optimistic=True` option to db_session
* Skip optimistic checks for queries in `db_session` with `serializable=True`
* `fk_name` option added for attributes in order to specify foreign key name
* #280: Now it's possible to specify `timeout` option, as well as pass other keyword arguments for `sqlite3.connect` function
* Add support of explicit casting to int in queries using `int()` function
* Added modulo division % native support in queries

# Bugfixes

* Fix bugs with composite table names
* Fix invalid foreign key & index names for tables which names include schema name
* For queries like `select(x for x in MyObject if not x.description)` add "OR x.info IS NULL" for nullable string columns
* Add optimistic checking for `delete()` method
* Show updated attributes when `OptimisticCheckError` is being raised
* Fix incorrect aliases in nested queries
* Correctly pass exception from user-defined functions in SQLite
* More clear error messages for `UnrepeatableReadError`
* Fix `db_session(strict=True)` which was broken in 2d3afb2
* Fixes #170: Problem with a primary key column used as a part of another key
* Fixes #223: incorrect result of `getattr(entity, attrname)` when the same lambda applies to different entities
* Fixes #266: Add handler to `"pony.orm"` logger does not work
* Fixes #278: Cascade delete error: FOREIGN KEY constraint failed, with complex entity relationships
* Fixes #283: Lost Json update immediately after object creation
* Fixes #284: `query.order_by()` orders Json numbers like strings
* Fixes #288: Expression text parsing issue in Python 3
* Fixes #293: translation of if-expressions in expression
* Fixes #294: Real stack traces swallowed within IPython shell
* `Collection.count()` method should check if session is alive
* Set `obj._session_cache_` to None after exiting from db session for better garbage collection
* Unload collections which are not fully loaded after exiting from db session for better garbage collection
* Raise on unknown options for attributes that are part of relationship
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