Code Challenge: database searching with peewee

Question

The objective was to write a function that would "Return all Challenges [database records] where the name field contains name argument and where the language field is equal to the language argument. "
Since this is a Python course, I interpreted "and" as boolean, to mean both
the name and language must match in a single record. Unaware (and too lazy to find out) how to combine
criteria in a single search/filter, I chose to filter the criteria sequentially:
```Python
from models import Challenge
def create_challenge(name, language, steps=1):
    Challenge.create(name=name,
                     language=language,
                     steps=steps)
def search_challenges(name, language):
    challenges = Challenge.select().where(Challenge.name == name)
    return challenges.where(Challenge.language == language)  
```
The "check work" feedback responded with "Bummer! Didn't find the right number of records". 
Trying to understand why, I wrote a script to test
filter criteria as arguments in a .where() function.
my test database has only 5 entries and 2 fields:  
    name: 'a' or 'b'  
    language: '1', '2', or '3'  
I combined name == 'a' and language = '1' in various searches. My script follows the output below.
2 questions:  
1) Why did sequential filtering of name then language fail the Treehouse challenge?
2) Can someone explain the 'and' and 'or' search results below?
output:  
.select()  
a 1  
a 2  
a 3  
b 1  
b 2  
name == 'a'  
a 1  
a 2  
a 3  
name == 'a' followed by language == '1'  
a 1  
(name == 'a') and (language == '1')  
a 1  
b 1  
(name == 'a') or (language == '1')  
a 1  
a 2  
a 3  
(name == 'a') & (language == '1')  
a 1  
(name == 'a') | (language == '1')  
a 1  
a 2  
a 3  
b 1  
```Python
from peewee import *
db = SqliteDatabase('throwaway.db')
class Test(Model):
    name = CharField(maxlength=10)
    language = CharField(maxlength=10)
class Meta:
    database = db
db.connect()
db.create_tables([Test], safe=True)
data = [('a', '1'), 
        ('a', '2'), 
        ('a', '3'), 
        ('b', '1'), 
        ('b', '2')]
for f1, f2 in data:
    Test.create(name=f1, language=f2)
def show(label, entries):
    print(label)
    for entry in entries:
        print('{} {}'.format(entry.name, entry.language))
    print()
allentries = Test.select()
show('.select()', allentries)
onlya = allentries.where(Test.name == 'a')
show("name == 'a'", only_a)
only1inonlya = onlya.where(Test.language == '1')
show("name == 'a' followed by language == '1'", only1inonly_a)
only1anda = allentries.where((Test.name == 'a') and 
                                 (Test.language == '1'))
show("(name == 'a') and (language == '1')", only1and_a)
only1ora = allentries.where((Test.name == 'a') or 
                                (Test.language == '1'))
show("(name == 'a') or (language == '1')", only1or_a)
only1ampa = allentries.where((Test.name == 'a') & 
                                 (Test.language == '1'))
show("(name == 'a') & (language == '1')", only1amp_a)
only1pipea = allentries.where((Test.name == 'a') | 
                                 (Test.language == '1'))
show("(name == 'a') | (language == '1')", only1pipe_a)
cleanup = Test.delete().where((Test.name == 'a'))
cleanup.execute()
cleanup = Test.delete().where((Test.name == 'b'))
cleanup.execute()
db.close()
```

Kenneth Love · Accepted Answer

You actually only need to include both criteria in your where.
python
Challenge.select().where(
    Challenge.name.contains(name),
    Challenge.language==language
)

But it's pretty awesome that you all went so far in researching/experimenting for this. I'll see about rewording the prompt a bit to make it less ambiguous.

ericb2 · Answer

(This is a comment, but posted as an answer because I have no idea how to post a single comment to multiple answers.  My ignorance of Markdown, HTML, tagging, and forums conspire to make this response very awkward.  I especially apologize to @Kenneth Love (https://teamtreehouse.com/kennethlove) and Chris Freeman if they were not tagged in this response; neither editor nor preview mode shows any indication that my selecting their names from the pop-up menu was successful.)
Thank you @chris freeman (https://teamtreehouse.com/chrisfreeman3) and Kenneth Love for your help. I wouldn't have understood my problem without both of your responses.  Chris, if this discussion has value to the forum, I think it will be because of the insights you shared and summarized so neatly.
I now see that my confusion about the challenge was due to misreading, arising from a bias towards the ways one might search search a string, list, dict, etc with two criteria, and from my unfamiliarity with peewee. My mind locked onto the 'and' as a familiar python concept but overlooked the peewee meaning of 'contains'. I also thought the statement to use '==' meant we were to apply it to each criteria.  
My tests only aggravated my misunderstanding because of a flawed premise; I failed to include a name that would match contains(name) but does not == name.
I notice Kenneth has thoughtfully changed the wording of the challenge.  
(ifIKnewHowToIndentI'dStartHere)  
Create a function named search_challenges that takes two arguments, name and language. Return all Challenges where the name field contains name argument and where the language field is equal to the language argument. Use == for equality. You don't need boolean and or binary & for this, just put both conditions in your where().  
(ifIKnewHowToIndentI'dEndHere)  
But, of all the people who have taken the challenge, no one else expressed any difficulty with it, so his re-wording is for people who think like me (a frightening thought).  The complication is, (a) the new wording might not have helped my original confusion, and (b) I worry that adding extra instruction may simply plant unnecessary concerns in people's minds, like telling someone to go to the grocery store and not to worry about elephants: it is more distraction than help. Perhaps simply monospacing the word 'contains' and make the tip about using '==' parenthetical inside the preceding sentence:
(ifIKnewHowToIndentI'dStartHere)  
Create a function named search_challenges that takes two arguments, name and language. Return all Challenges where the name field contains name argument and where the language field is equal (Use ==) to the language argument.  
(ifIKnewHowToIndentI'dEndHere)  
It's just a thought.
p.s.  
Kenneth, while I have your attention, I just finished your Python Track and wanted to say,
Python
        kenneth_love_videos == (clear * educational * FUN)

Thank you!

Chris Freeman · Answer

The CRUD: Search Function (/library/using-databases-in-python/gettin-crudy-with-it/crud-search-function) challenge definitely stretches the readers interpretation.
Original wording: Return all Challenges where the name field contains name argument and where the language field is equal to the language argument. Use == for equality.
It wasn't until after trying to logically "and" the two requirements, that I eventually tried a logical-OR.
The wording should have include the wording:
using either/or: Return all Challenges where either the name field contains name argument or where the language field is equal to the language argument. Use == for equality.
or it should have had a comma after the first where to emphasize a "plus" type "and" instead of a logical-and, but that is also very subtle:
Adding a comma: Return all Challenges where the name field contains name argument, and where the language field is equal to the language argument. Use == for equality.
As for your questions regarding the difference between "and" vs "&"; "or" vs "|", I looked through the peewee (http://peewee.readthedocs.org/en/latest/index.html) documentation.  In your test examples the logical operators "&", and "|" appear to work as expected..  Specifically the "&" matching the chaining of where() filters.  So what is the difference between "&" and "and"?
The peewee docs section on query operators (http://peewee.readthedocs.org/en/latest/peewee/querying.html#query-operators)
has a stern warning:
Warning
Although you may be tempted to use python’s in, and, or and not operators in your query expressions, these will not work. The return value of an in expression is always coerced to a boolean value. Similarly, and, or and not all treat their arguments as boolean values and cannot be overloaded.
So just remember:
Use << instead of in
Use & instead of and
Use | instead of or
Use ~ instead of not
Don’t forget to wrap your comparisons in parentheses when using logical operators.
Perhaps, @Kenneth Love (https://teamtreehouse.com/kennethlove) might want to consider rewording the challenge question.

Kenneth Love · Answer

Oh, also, if I mean the and boolean, it'll be in our code font (like the one in this sentence) and not just in the regular font.

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ericb2

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Code Challenge: database searching with peewee

Chris Freeman

Chris Freeman

4 Answers

Kenneth Love

Kenneth Love

Chris Freeman

Chris Freeman

Yuda Leh

Yuda Leh

Kenneth Love

Kenneth Love

kyle madson

kyle madson

Chris Freeman

Chris Freeman

Cristian Romero

Cristian Romero

ericb2

ericb2

Chris Freeman

Chris Freeman

Kenneth Love

Kenneth Love