Organize app queries in an annotated SQL file.
Query selector allows one treat a file full of SQL queries as a record, with one attribute for each annotated query. This makes working with long, ad-hoc SQL queries more hygienic, and has the benefit of making it easy to find the queries.
The QuerySelector constructor accepts a string, file handle or (<package>, <resource) pair and parses the SQL into groups annotated with --@ <name> <mode>. The <name> is any Python compatible name; it will become an attribute of the object. The <mode> is merely metadata, and can be omitted; it describes whether a query should have one, none or many results.
For example, a file like this:
--@ t one SELECT now();
becomes an object with a single attribute t:
>>> q.t Query(args=, mode=u'one', readonly=False, text=u'SELECT * FROM now();')
A QuerySelector object is iterable, providing pairs of name and query in the order that the queries originally appeared in the file.
>>> for name, q in qs: ... print '%s: %s' % (name, q) t: Query(args=, mode=u'one', readonly=True, text='SELECT now();')
Modes can be one of none, one, one? and many. When not specified, default is many. A mode string can also be followed with the single word ro as a clue that the query is read-only.
Realistically, SELECT now() is a read-only query. We can annotate it as such, the resulting query datastructure records this:
>>> QuerySelector(""" ... --@ t one ro ... SELECT now(); ... """).t Query(args=, mode=u'one', readonly=True, text=u'SELECT * FROM now();')
query-selector recognizes the %(...)s style parameter references defined in Python DBI 2.0. Say that we’d like to pass a timezone when selecting the server time. We can do so by adding AT TIME ZONE %(tz)s to our query. The presence of this parameter is stored in the args field of the parsed result. (The parameters in .args are listed in the order of their first appearance in the query.)
>>> QuerySelector(""" ... --@ t one ro ... SELECT now() AT TIME ZONE %(tz)s AS t; ... """).t Query(args=[u'tz'], mode=u'one', readonly=True, text=u'SELECT now() AT TIME ZONE %(tz)s AS t;')