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iter_fetchmany

Author:
jdunck
Posted:
January 8, 2009
Language:
Python
Version:
1.0
Tags:
sql db db-api fetchmany
Score:
0 (after 0 ratings)

When executing custom sql, the temptation is to use fetchall or fetchone, since the API for fetchmany is a bit awkward. (fetchall makes all records resident in client memory at once; fetchone takes a network round-trip to the DB for each record.)

This snippet, hoisted from django.db.models.sql.query.results_iter, presents a nice, simple iterator over multiple fetchmany calls which hits a sweet spot of minimizing memory and network usage.

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def iter_fetchmany(cursor, size=100): 
    """ 
    Handles the awkwardness of iterating using fetchmany, and exposes all records as a (generated) iterable. 
 
    Assumes django.db is the connection for the given cursor.  FIXME for multi-db support. 
    """ 
    from django.db import connection 
    rowset_iter = iter((lambda: cursor.fetchmany(size)), 
            connection.features.empty_fetchmany_value) 
    for rows in rowset_iter: 
        for row in rows: 
            yield row 

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