In the description of filtering records in Peewee, there are examples of two alternative syntaxes: using commas to separate multiple conditions, such as the following example,
Tweet.select().where(Tweet.user == user, Tweet.is_published == True)
and using bitwise operators. I cannot figure out (and cannot find a description of) the difference between using the comma syntax and using bitwise operators. What does the comma syntax actually do? From the (single) documented example of using a comma, it seems like it might be equivalent to using &, as in
Tweet.select().where( (Tweet.user == user) & (Tweet.is_published == True) )
Is that the case?
Yes, they are equivalent, as per the code:
def where(self, *expressions):
if self._where is not None:
expressions = (self._where,) + expressions
self._where = reduce(operator.and_, expressions)
Related
How do we write conditions in arango, that includes for loops. I can elaborate the requirement below.
My requirement is if a particular attribute(array type) exists in the arango collection, i would read data from the collection(that requires a loop) or else, might do the following :
return null
return empty string ""
do nothing.
Is this possible to achieve in arango?
The helping methods could be -->
-- has(collectionname, attributename)
-- The ternary operator ?:
let attribute1 = has(doc,"attribute1") ?(
for name in doc.attribute1.names
filter name.language == "xyz"
return name.name
) : ""
But this dosent work. Seems like arango compiler first attempts to compile the for loop, finds nulls and reports error as below. Instead, it should have compiled "has" function first for the ternary operator being used.
collection or array expected as operand to FOR loop; you provided a value of type 'null' (while executing)
If there is a better way of doing it, would appreciate the advice!!
Thanks in advance!
Nilotpal
Fakhrany here from ArangoDB.
Regarding your question, this is a known limitation.
From https://www.arangodb.com/docs/3.8/aql/fundamentals-limitations.html:
The following other limitations are known for AQL queries:
Subqueries that are used inside expressions are pulled out of these
expressions and executed beforehand. That means that subqueries do not
participate in lazy evaluation of operands, for example in the ternary
operator. Also see evaluation of subqueries.
Also noted here for the ternary operator:
https://www.arangodb.com/docs/3.8/aql/operators.html#ternary-operator.
An answer to the question what to do may be to use a FILTER before enumerating over the attributes:
FOR doc IN collection
/* the following filter will only let those documents passed in which "attribute1.names" is an array */
FILTER IS_ARRAY(doc.attribute1.names)
FOR name IN doc.attribute1.names
FILTER name.language == "xyz"
RETURN name.name
Other solutions are also possible. Depends a bit on the use case.
I can find similar strings with the following command, but instead of using a string, I need to use a variable to find similar values between two columns.
df.filter(df.column_name.like("%Spark%")).show()
pattern = "Spark"
df.filter(df.column_name.like("%" + pattern + "%")).show()
A perhaps better way is to use rlike with a regex pattern to take care of word boundaries:
pattern = "Spark"
df.filter(df.column_name.rlike("\\b" + pattern + "\\b")).show()
I cannot find where to quote a field name that has a space in it, for example when doing
FILTER s._key = a.`Supplier Id`
The above, sql-style quote doesn't work, neither does array access. What's the correct way?
Figured it out now, I got bitten by SQL and forgot that equality comparison is made with == in AQL. Then the array access worked, so the way to use field names with spaces is this:
FILTER s._key == a['Supplier Id']
If the field is without spaces but has some special characters, it works to use backtick instead of array access:
FILTER s._key == a.`ÅterförsäljareId`
Edit: Another option is to use bind variables:
FILTER s._key == a.#field
// Passing this to the API as bind variables:
{
"field": "Supplier Id"
}
I currently have an assignemnt where i have to handle data from a lot of countries. My customer have given me a list of acceptable characters, lets call it:
'aber =*'
All other characters should just be changed to '_'.
I know the conversion for my country's specific chars (æøå), easily done with something like
select replace ('Ål', 'Å', 'AA') from dual;
But how would i go about removing all unwanted "noise" without splitting it up in char-by-char comparison?
For example "bear*2 = fear" should become "bear*_ = _ear" as 2 and f are not in the accepted list.
Oracle 10g and up. As one of the approaches, you can use regular expression function regexp_replace():
select regexp_replace('bear*2 = fear', '[^aber =*]', '_') as res
from dual
res
------------------------------
bear*_ = _ear
Find out more about regexp_replace() function.
I need to validate for valid code name.
So, my string can have values like below:
String test = "C000. ", "C010. ", "C020. ", "C030. ", "CA00. ","C0B0. ","C00C. "
So my function needs to validate below conditions:
It should start with C
After that next 3 characters should be numeric before .
Rest it can be anything.
So in above string values, only ["C000.", "C010.", "C020.", "C030."] are valid ones.
EDIT:
Below is the code I tried:
if (nameObject.Title.StartsWith(String.Format("^[C][0-9]{3}$",nameObject.Title)))
I'd suggest a regex, for example (written off the top of my head, may need work):
string s = "C030.";
Regex reg = new Regex("C[0-9]{3,3}\\.");
bool isMatch = reg.IsMatch(s);
This regex should do the trick:
Regex.IsMatch(input, #"C[0-9]{3}\..*")
Check out http://www.techotopia.com/index.php/Working_with_Strings_in_C_Sharp
for a quick tutorial on (among other things) individual access of string elements, so you can test each element for your criteria.
If you think your criteria may change, using regular expressions gives you maximum flexibility (but is more runtime intensive than regular string-element evaluation). In your case, it may be overkill, IMHO.