[PYTHON DB-SIG] DB-Modules returning lists of dicts
Thu, 09 Jan 1997 10:25:00 -0500
I'm afraid that I don't have enough time to participate in this list
like I would like to. I haven't been able to follow this thread very
closely, but I feel that I need to spend a little badwidth here to make
some points I've made before, but that have probably been forgotten.
1. At one point, I thought there was agreement that data should be
returned in Database tuple objects, not Python tuples. Database
tuple objects provide sequence, mapping, and getattr interfaces.
For example, assume that you have a table with columns a, b, and c.
If I have a database tuple, t, then I can:
t # Get value of b for t
t.b # ditto
t['b'] # ditto
t=42 # Set value of b for t to 42
#(for database interfacess that allow this)
t.b=42 # ditto
t['b']=42 # ditto
Database tuples store data internally as a C array of object pointers
and a pointer to a shared meta-data object that has the data
to do name->column mappings. So the implementation is essentially as
efficient as Python tuples and yet provides name-based interfaces.
I have implemented this mechanism for several database interfaces
I did at USGS, but these were never released. :-(
I feel very strongly that this is the "right" way to model result
2. I don't particularly like the current database API. I favor an
API that I consider far more natural. Unfortunately, I don't have
to develop a detailed proposal. Here is a high-level sketch:
Replace "cursors" with database table objects.
db=spamdb.Database(whatever) # Create a database connection
table=db.execute("select * from spam") # This creates a database
# table object
Note that, on systems that use cursors, table objects wrap cursors
make the cursor look like a sequence of database records. We don't
all of the data into memory at once. Rather, as we sequentially
data, the data are fetched, one row at a time. The most common way
to access the data will be via a for loop:
for row in table:
# Do stuff with the row, like, maybe printing out the values
# for column a
Note that we could combine the table creation with the for:
for row in db.execute("select * from spam"): ...
We can also do non-select statements, as in:
db.execute("create table eggs ...")
If you want to get all of the data at once, you can use a slice:
data=db.execute("select * from spam")[:]
And we can compile parameterized statements for use later as
f=db.prepare("select * from spam where ni=%s")
This creates a compiled statement that has a single string parameter.
A database-independent string format should be used, IMO. Now the
compiled statement is used like any other Python callable object:
for t in f("bar")
Databse connections may be closed explicitly:
or implicitly when the database is GCed, as with file objects.
My $0.02. Sorry it isn't more. Silence is not assent.
Jim Fulton Digital Creations
## Python is my favorite language ##
## http://www.python.org/ ##
DB-SIG - SIG on Tabular Databases in Python
send messages to: email@example.com
administrivia to: firstname.lastname@example.org