On 06/15/2016 01:37 PM, Mike Bayer wrote: > > > On 06/15/2016 01:34 PM, Mike Bayer wrote: >> >> >> On 06/15/2016 12:40 PM, Jonathan Rogers wrote: >>> On Friday, February 25, 2011 at 10:27:34 AM UTC-5, Michael Bayer wrote: >>> >>> >>> On Feb 25, 2011, at 10:20 AM, Jon Nelson wrote: >>> >>> > On Fri, Feb 25, 2011 at 9:15 AM, Michael Bayer >>> <mik...@zzzcomputing.com <javascript:>> wrote: >>> >> % is significant in DBAPIs like postgresql and mysqldb where >>> pyformat and format: %(foo)s and %s, are allowed, so % must be >>> doubled. >>> > >>> > So does psycopg2 send '%' or '%%' ? >>> >>> psycopg2 is the DBAPI here, % is significant so the client of DBAPI >>> must escape % that is not part of a string format. >>> >>> >>> > It seems to me that if the >>> > strings are held as atoms (individual arguments rather than a >>> single, >>> >>> sorry, I don't know what you mean by "individual arguments", do you >>> mean bind params, i.e. :p1 + :p2 + :p3 ? >>> >>> > concatenated string) then '%%' is unnecessary. >>> >>> >>> The compiler most certainly needs to escape literal-rendered % signs >>> across the board on those DBAPIs where the symbol has other >>> meanings, since a user might use literal_column() with a '%' sign in >>> it, and would like this symbol to behave the same way on all >>> backends. >>> >>> >>> >>> I can understand why a '%' needs to be doubled in a typical statement >>> such as a select. However, I also see a '%' doubled inside the >>> definition of a CheckConstraint when I compile and print a Table >>> containing the CheckConstraint object for the purpose of generating a >>> DDL script. The constraint expression should be left alone. In Postgres, >>> '%%' means the same as '%' when used with LIKE, but I'd still like to >>> avoid the unnecessary doubling. >> >> the escaping is to get around the DBAPI itself (e.g. psycopg2) which >> wishes to apply pyformat substitution to the string. > > also note, using the non-DBAPI level dialect (in this case PGDialect), > you don't get the percent signs: > > from sqlalchemy.dialects import postgresql > from sqlalchemy.schema import CreateTable > print CreateTable(t).compile(dialect=postgresql.base.PGDialect()) > > CREATE TABLE t ( > x VARCHAR(50), > CHECK (x != 'foo%') > ) > > > so I'd use that for DDL rendering as scripts.
That's exactly what I needed to know. I had been using sqlalchemy.dialects.postgresql.dialect(). Thanks for the swift reply as usual. -- Jonathan Rogers -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
