Changes between Version 47 and Version 48 of DeveloperGuidelines/Optimisation

Timestamp:

06/18/10 09:25:15 (15 years ago)

Author:

Dominic König

Comment:

--

DeveloperGuidelines/Optimisation

@@ -71 +71 @@
 == Golden Rules for DB Queries ==
 
-These "rules" might seem a matter of course, however, sometimes you need to take a second look at your code:
- * Insert a temporary {{{print >> sys.stderr, self.query}}} into web2py's {{{select()}}} function and take a look at what it says.
+  These "rules" might seem a matter of course, however, sometimes you need to take a second look at your code:
 
 === Use Joins ===
@@ -174 +173 @@
 }}}
 
+Or more complex:
+
+{{{
+for x in y:
+    if x.a == some_value or other_variable == other_value:
+        record = db(db.mytable.id == x.key).select()
+        ...<branch 1>
+    else:
+        record = db(db.othertable.id == x.other_key).select()
+        ...<branch 2>
+}}}
+
+could be:
+
+{{{
+if other_variable == other_value:
+    ids1 = [x.key for x in y]
+    ids2 = []
+else:
+    ids1 = filter(lambda x: (x.a == some_value) and x.key or None, y)
+    ids2 = filter(lambda x: (x.a != some_value) and x.other_key or None, y)
+if ids1:
+    records = db(db.mytable.id.belongs(ids1)).select()
+    for record in records:
+        ...<branch 1>
+if ids2:
+    records = db(db.othertable.id.belongs(ids2)).select()
+    for record in records:
+        ...<branch 2>
+}}}
+
 ----
 DeveloperGuidelines
+DeveloperGuidelines