Hi,
I'm working on an application where queries are created completely by
the user. (The goal is to make it easy for the user). Because of this
I have to support dynamic query creation and manipulation. My current
model has a query class with my own created specification for queries
which is manipulated by the user via the GUI. This is then turned into
an SQLA query when it's run. Well, it will be turned into one.
I'm trying to wrap my head around building the WHERE clause. I find
that when a function returns a condition (age > 18 for example) it
comes with brackets around it. However, when I enter it into the where
function directly it doesn't unless it uses an SQLA method like
column.in_(stuff) .
I have some test code I've been playing with below:
def condition(age,b):
return age > b
name = tableObjects['users'].c['name']
age = tableObjects['users'].c['age']
password = tableObjects['users'].c['password']
q = select([tableObjects['users']])
names = ('Mark','Joel')
#the query construction
a = (name.in_(names))
# I enter it into the where method directly:
q = q.where(name.in_(names)+age>18+~password.like('v'))
#Results in:
#WHERE (users.name IN (?, ?)) + users.age > ? + (users.password NOT
LIKE ?)
# If functions build the term:
expr = name.in_(names) + condition(age,18)
q = q.where(expr) # If placed in where(expr) it results in WHERE
(users.name IN (?, ?)) + (users.age > ?)
# Note extra brackets
result = dataConnections['sqlite:///tutorial.db'].execute(q)
for row in result:
print row
Would the brackets make any difference to the performance? (They
wouldn't make any meaningful difference to the result as far as I can
see)
I've recently noticed the serializer for SQLA queries. How easy would
it be to save them with IDs? Also, is it easy to manipulate and adjust
a specific piece of a query? Like, the second element of a nested
where clause? If it is, my separate class system may be unnecessary
overhead (unless I decide the ability to port to other libraries is
really important...).
Thanks,
Edward
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