How to create a dynamic filter?

Question

I have a table with equipment and each of them has dates for level of maintenance. The user can select the maintenance level. So, I should adjust my SQLAlchemy for each combination of maintenance level chosen. For example:

SELECT * WHERE (equipment IN []) AND m_level1 = DATE AND m_level2 = DATE ....)

So it is possible to have combinations for each if condition, depending on checkboxes I used multiple strings to reach my goal, but I want to improve the query using SQLAlchemy.

Asked By: Lorenzo Simonassi

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Source

Answer 1

I assume you are using the ORM.

in that case, the filter function returns a query object. You can conditionaly build the query by doing something like

query = Session.query(schema.Object).filter_by(attribute=value)
if condition:
    query = query.filter_by(condition_attr=condition_val)
if another_condition:
    query = query.filter_by(another=another_val)

#then finally execute it

results = query.all()

Answered By: Busturdust

Answer 2

The function filter(*criterion) means you can use tuple as it’s argument, @Wolph has detail here:
SQLALchemy dynamic filter_by for detail

Answered By: chenxin

Answer 3

if we speak of SQLAlchemy core, there is another way:

from sqlalchemy import and_


filters = [table.c.col1 == filter1, table.c.col2 > filter2]
query = table.select().where(and_(*filters))

If you’re trying to filter based on incoming form criteria:

form = request.form.to_dict()
filters = []
for col in form:
    sqlalchemybinaryexpression = (getattr(MODEL, col) == form[col])
    filters.append(sqlalchemybinaryexpression)
query = table.select().where(and_(*filters))

Where MODEL is your SQLAlchemy Model

Answered By: igolkotek

Answer 4

Another resolution to this question, this case is raised in a more secure way, since it verifies if the field to be filtered exists in the model.

To add operators to the value to which you want to filter. And not having to add a new parameter to the query, we can add an operator before the value e.g ?foo=>1, ‘?foo=<1,?foo=>=1, ?foo=<=1 ‘, ?foo=!1,?foo=1, and finally between which would be like this `?foo=a, b’.

from sqlalchemy.orm import class_mapper
import re

# input parameters
filter_by = {
  "column1": "!1", # not equal to
  "column2": "1",   # equal to
  "column3": ">1",  # great to. etc...
}

def computed_operator(column, v):
  if re.match(r"^!", v):
    """__ne__"""
    val = re.sub(r"!", "", v)
    return column.__ne__(val)
  if re.match(r">(?!=)", v):
    """__gt__"""
    val = re.sub(r">(?!=)", "", v)
    return column.__gt__(val)
  if re.match(r"<(?!=)", v):
    """__lt__"""
    val = re.sub(r"<(?!=)", "", v)
    return column.__lt__(val)
  if re.match(r">=", v):
    """__ge__"""
    val = re.sub(r">=", "", v)
    return column.__ge__(val)
  if re.match(r"<=", v):
    """__le__"""
    val = re.sub(r"<=", "", v)
    return column.__le__(val)
  if re.match(r"(w*),(w*)", v):
    """between"""
    a, b = re.split(r",", v)
    return column.between(a, b)
  """ default __eq__ """
  return column.__eq__(v)

query = Table.query
filters = []
for k, v in filter_by.items():
  mapper = class_mapper(Table)
  if not hasattr(mapper.columns, k):
    continue
  filters.append(computed_operator(mapper.columns[k], "{}".format(v))
query = query.filter(*filters)
query.all()

Answered By: frfernandezdev

Answer 5

Here is a solution that works both for AND or OR…

Just replace or_ with and_ in the code if you need that case:

from sqlalchemy import or_, and_

my_filters = set() ## <-- use a set to contain only unique values, avoid duplicates

if condition_1:
    my_filters.add(MySQLClass.id == some_id)
if condition_2:
    my_filters.add(MySQLClass.name == some_name)

fetched = db_session.execute(select(MySQLClass).where(or_(*my_filters))).scalars().all()

Answered By: elano7

How to create a dynamic filter?

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