I don't know if the title of the question is formed well enough. But essentially I would like to be able to do something like this from front end :
(name="abc" OR name="xyz") AND (status="active" OR (status="available" AND age=30))
I want to the user to send this string. I will parse it in backend and form a query.
I have looked at this answer and this but couldn't figure out how to solve the parenthesis here.
I am thinking about using a stack (the way we solve infix expressions) to do this, but don't want to go that long route unless I am sure there isn't another/ready solution available. If someone can do this with that method, would be great too.
So I got it done using by changing the 'infix expression solver' a bit.
Here's the code:
def complex_filter_by_string(mystr):
"""
Filters string by using Q objects and infix expression solver.
The input string should be of the type ( name = abc OR name = xyz ) AND ( other = fgh ) Or ( other_one = xyz )
Notice the spaces after each 'word'. We are splitting the string by space, so space is necessary.
"""
tokens = mystr.split()
# stack to store integer values.
values = []
# stack to store operators.
ops = []
i = 0
while i < len(tokens):
# Current token is a whitespace,
# skip it.
if tokens[i] == ' ':
i += 1
continue
# Current token is an opening
# brace, push it to 'ops'
elif tokens[i] == '(':
ops.append(tokens[i])
# Current token is =, convert it to a Q object and push
# it to stack for q objects.
elif tokens[i] == "=":
# if token equals '=' . It means we will have tokens[i-1]=attribute and tokens[i+1]=value (this is a constraint on string)
obj = {}
key = tokens[i-1]
value = tokens[i+1]
if isinstance(value,str):
i+=1
while i+1 < len(tokens) and (tokens[i+1] != 'OR' and tokens[i+1] != 'AND' and tokens[i+1] != ')'):
value= value + " " + tokens[i+1]
i+=1
value = value.rstrip()
obj[key]=value
val = Q(**obj)
values.append(val)
# Closing brace encountered,
# solve entire brace.
elif tokens[i] == ')':
while len(ops) != 0 and ops[-1] != '(':
val2 = values.pop()
val1 = values.pop()
op = ops.pop()
values.append(applyOp(val1, val2, op))
# pop opening brace.
ops.pop()
# Current token is an operator.
elif tokens[i] == "OR" or tokens[i] == "AND":
# While top of 'ops' has same or
# greater precedence to current
# token, which is an operator.
# Apply operator on top of 'ops'
# to top two elements in values stack.
while (len(ops) != 0 and
precedence(ops[-1]) >=
precedence(tokens[i])):
val2 = values.pop()
val1 = values.pop()
op = ops.pop()
values.append(applyOp(val1, val2, op))
# Push current token to 'ops'.
ops.append(tokens[i])
i += 1
# Entire expression has been parsed
# at this point, apply remaining ops
# to remaining values.
while len(ops) != 0:
val2 = values.pop()
val1 = values.pop()
op = ops.pop()
values.append(applyOp(val1, val2, op))
# Top of 'values' contains result,
# return it.
return values[-1]
This will return a Q object which you can pass onto your model lie MyModel.objects.filter(q_obj)
There are a few restrictions on the string though. The main restriction is 'there should be a whitespace after each keyword'. A keyword can be ' OR , AND , attribute , value , = , open_parenthesis '.
So the string that i posted in question should be : ( name = abc OR name = xyz ) AND (status = active OR ( status = available AND age = 30 ))