GROUP_CONCAT, and similar functions

[James Hooker]

Hey - loving the library, very cool, but I have a quick question.

I've searched through the docs, and the source, but can see no mention of using functions like 'GROUP_CONCAT'. Should I just execute a raw query against a result set in order to use actions like this?

I know these functions are not neccesarily available across all DB Engines, so can understand why you wouldn't include support by default.

Thanks

p.s. I am using sqlite3 currently as my DB Engine

[Charles Leifer]

You can use `fn`:

from peewee import fn

fn.Group_Concat(...)

fn.Count(...)

fn.Substr(fn.Lower(..)...)

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[James Hooker]

Hi Charles,

That's great, thanks! I was already using fn for 'count', but I guess I didn't fully grasp this functionality.

Thanks for the clarification!

James H

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[A.L. Kleijngeld]

Hi,

This post was certainly useful to me, but I was wondering if it possible to pass along an alternative separator character? Using MySQL, I now have:

fn.Group_Concat(Person.first_name, ' ', Person.last_name).alias('directors')

Which results in "Satoshi Kon,Shôgo Furuya". I would like to use the seperator ', ' (including the space, so it would result in "Satoshi Kon, Shôgo Furuya". In MySQL this is done with the seperator keyword.

Thank you!

[Charles Leifer]

Yeah this gets a little bit gross because the function call joins its arguments with commas, but the "SEPARATOR <foo>" bit needs to go after the last argument.  Here is one way that might work:

fn.GROUP_CONCAT(Person.first_name, Clause(Person.last_name, SQL("SEPARATOR ', '")))

And another way that might:

fn.GROUP_CONCAT(

  Clause(

    CommaClause(Person.first_name, Person.last_name), 

    SQL("SEPARATOR ', '")  # CommaClause is multiple nodes joined by commas

  )  # Clause is multiple nodes joined by spaces

)

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