criteria-pattern 4.0.0

The Criteria Pattern is a Python package that simplifies and standardizes criteria based filtering, validation and selection.

🤏🏻 Criteria Pattern

The Criteria Pattern is a Python 🐍 package that simplifies and standardizes criteria based filtering 🤏🏻, validation and selection. This package provides a set of prebuilt 👷🏻 objects and utilities that you can drop into your existing projects and not have to implement yourself.

These utilities 🛠️ are useful when you need complex filtering logic. It also enforces 👮🏻 best practices so all your filtering processes follow a uniform standard.

Easy to install and integrate, this is a must have for any Python developer looking to simplify their workflow, enforce design patterns and use the full power of modern ORMs and SQL 🗄️ in their projects 🚀.

Table of Contents

• 📥 Installation
• 📚 Documentation
• ✨ Features
• 💻 Utilization
  • 🧱 Core Concepts
  • 🧮 Supported Operators
  • 🔄 Available Converters
  • 🔐 Security For User-Facing APIs
  • 🛡️ SQL Conversion And Safety
  • 📦 Request Body Examples
  • 🧭 Structured URL Query Examples
  • 🎯 Real-Life Case: Multi-tenant User Search Service
  • 🔎 Simple URL Query Examples
  • 🧪 Testing Helpers
• 🤝 Contributing
• 🔑 License

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📥 Installation

You can install Criteria Pattern using pip:

pip install criteria-pattern

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📚 Documentation

The root README is the entry point. Deeper guides live in this repository and are linked here:

• 🧱 Usage Guide: Core models, composition rules, operators and pagination.
• 🔄 Converter Guide: SQL converters, request converters, placeholder styles and mapping.
• 🔐 Security Guide: User-facing criteria safety and injection prevention.
• 🧪 Testing Guide: Object mother helpers and testing recommendations.

This project's DeepWiki documentation is also available for generated repository navigation.

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✨ Features

Criteria Pattern gives you a typed, reusable way to describe queries before deciding how they should be executed.

• 🧱 Composable criteria objects with filters, orders, page size and page number.
• 🔗 Boolean composition with &, | and ~ for AND, OR and NOT logic.
• 🔎 20 filter operators covering equality, comparison, pattern matching, ranges, null checks and list membership.
• ↕️ Ordering primitives with duplicate order-field protection.
• 📄 Pagination primitives that enforce positive integer values and consistent page-number usage.
• 🗄️ SQL converters for PostgreSQL, MySQL, MariaDB and SQLite.
• 🧾 Request converters for decoded request bodies, structured URL queries and compact suffix-based URL queries.
• 🛡️ Security-oriented allowlist validation for tables, columns, fields, operators, directions and pagination bounds.
• 🧰 Field and operator mapping so public API names can be translated to internal model or database names.
• 🧪 Object mother testing helpers for downstream projects that want realistic criteria fixtures.

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💻 Utilization

from criteria_pattern import Criteria, Filter, Operator
from criteria_pattern.converters import CriteriaToPostgresqlConverter

is_adult = Criteria(filters=[Filter(field='age', operator=Operator.GREATER_OR_EQUAL, value=18)])
email_is_gmail = Criteria(filters=[Filter(field='email', operator=Operator.ENDS_WITH, value='@gmail.com')])
email_is_yahoo = Criteria(filters=[Filter(field='email', operator=Operator.ENDS_WITH, value='@yahoo.com')])

query, parameters = CriteriaToPostgresqlConverter.convert(
    criteria=is_adult & (email_is_gmail | email_is_yahoo),
    table='user',
    valid_columns=['age', 'email'],
    valid_operators=[Operator.GREATER_OR_EQUAL, Operator.ENDS_WITH],
)
print(query)
print(parameters)
# >>> SELECT * FROM "user" WHERE ("age" >= %(parameter_0)s AND ("email" LIKE '%%' || %(parameter_1)s OR "email" LIKE '%%' || %(parameter_2)s));
# >>> {'parameter_0': 18, 'parameter_1': '@gmail.com', 'parameter_2': '@yahoo.com'}

🧱 Core Concepts

The main model is Criteria. A criteria can contain filters, orders and pagination:

from criteria_pattern import Criteria, Direction, Filter, Operator, Order


criteria = Criteria(
    filters=[
        Filter(field='status', operator=Operator.EQUAL, value='ACTIVE'),
        Filter(field='age', operator=Operator.GREATER_OR_EQUAL, value=18),
    ],
    orders=[
        Order(field='created_at', direction=Direction.DESC),
    ],
    page_size=20,
    page_number=1,
)

Criteria can be composed without losing the boolean structure:

from criteria_pattern import Criteria, Filter, Operator


is_active = Criteria(filters=[Filter(field='status', operator=Operator.EQUAL, value='ACTIVE')])
is_adult = Criteria(filters=[Filter(field='age', operator=Operator.GREATER_OR_EQUAL, value=18)])
has_company_email = Criteria(filters=[Filter(field='email', operator=Operator.ENDS_WITH, value='@acme.com')])

criteria = is_active & (is_adult | has_company_email)
not_archived = ~Criteria(filters=[Filter(field='archived_at', operator=Operator.IS_NOT_NULL, value=None)])

Pagination is optional. page_size can be used alone for LIMIT, while page_number must be used with page_size so converters can calculate the offset.

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🧮 Supported Operators

Operator	Meaning	Expected value
EQUAL	Field equals value	scalar
NOT_EQUAL	Field does not equal value	scalar
GREATER	Field is greater than value	scalar
GREATER_OR_EQUAL	Field is greater than or equal to value	scalar
LESS	Field is less than value	scalar
LESS_OR_EQUAL	Field is less than or equal to value	scalar
LIKE	SQL-like pattern match	scalar pattern
NOT_LIKE	SQL-like pattern negation	scalar pattern
CONTAINS	Field contains value	scalar
NOT_CONTAINS	Field does not contain value	scalar
STARTS_WITH	Field starts with value	scalar
NOT_STARTS_WITH	Field does not start with value	scalar
ENDS_WITH	Field ends with value	scalar
NOT_ENDS_WITH	Field does not end with value	scalar
BETWEEN	Field is between two values	two values
NOT_BETWEEN	Field is not between two values	two values
IS_NULL	Field is null	ignored / None
IS_NOT_NULL	Field is not null	ignored / None
IN	Field is one of many values	one or more values
NOT_IN	Field is not one of many values	one or more values

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🔄 Available Converters

The package includes converters for SQL generation and request parsing:

• criteria_pattern.converters.CriteriaToPostgresqlConverter: Converts a Criteria object into PostgreSQL SQL + parameters.
• criteria_pattern.converters.CriteriaToMysqlConverter: Converts a Criteria object into MySQL SQL + parameters.
• criteria_pattern.converters.CriteriaToMariadbConverter: Converts a Criteria object into MariaDB SQL + parameters.
• criteria_pattern.converters.CriteriaToSqliteConverter: Converts a Criteria object into SQLite SQL + parameters.
• criteria_pattern.converters.SimpleUrlToCriteriaConverter: Parses simple public URL query parameters into a Criteria object.
• criteria_pattern.converters.UrlToCriteriaConverter: Parses URL query parameters into a Criteria object.
• criteria_pattern.converters.BodyToCriteriaConverter: Parses decoded request bodies into a Criteria object.

SQL converter output uses the placeholder style expected by each database family:

Converter	Placeholder style	Parameters
CriteriaToPostgresqlConverter	%(parameter_0)s	dict[str, object]
CriteriaToMysqlConverter	%s	list[object]
CriteriaToMariadbConverter	%s	list[object]
CriteriaToSqliteConverter	:parameter_0	dict[str, object]

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🔐 Security For User-Facing APIs

When criteria comes from a URL, JSON body, form, dashboard or any other user-facing surface, treat every field, operator, direction and pagination value as untrusted.

Criteria Pattern parameterizes filter values for SQL converters, quotes SQL identifiers per dialect, and enables allowlist validation by default. SQL identifiers still cannot be safely parameterized by database drivers, so for user-facing APIs you must pass explicit valid_* allowlists instead of relying on implicit defaults derived from the current criteria.

Use this rule of thumb:

Input kind	Risk	Recommended protection
Filter values like 'Doe', 18 or ['ACTIVE']	SQL value injection	Handled by converter parameters
Table names	SQL identifier injection	valid_tables allowlist (validation on by default)
Selected columns	SQL identifier injection	valid_columns allowlist (validation on by default)
Filter and order fields	SQL identifier injection	valid_fields when parsing; valid_columns with mapped SQL column names when converting
Operators	Query behavior abuse	valid_operators allowlist with only the operators you expose
Directions	Query behavior abuse	valid_directions allowlist
Page size and page number	Expensive queries / overflow	strict max_page_size / max_page_number (validation on by default)

The safest user-facing flow is:

1. Keep allowlists in application code, not in request data.
2. Parse request input with BodyToCriteriaConverter, UrlToCriteriaConverter or SimpleUrlToCriteriaConverter.
3. Map public field names to internal field or column names with fields_mapping.
4. Enable field, operator, direction and pagination validation in the request converter.
5. Enable table, column, criteria, operator, direction and pagination validation again in the SQL converter.

from criteria_pattern import Direction, Operator
from criteria_pattern.converters import BodyToCriteriaConverter, CriteriaToPostgresqlConverter


body = {
    'filters': [{'field': 'q', 'operator': 'contains', 'value': 'Doe'}],
    'orders': [{'field': 'created', 'direction': 'DESC'}],
    'page_size': 20,
    'page_number': 1,
}

fields_mapping = {'q': 'name', 'created': 'created_at'}
valid_fields = ['name', 'created_at']
valid_operators = [Operator.CONTAINS]
valid_directions = [Direction.DESC]

criteria = BodyToCriteriaConverter.convert(
    body=body,
    fields_mapping=fields_mapping,
    check_field_injection=True,
    check_operator_injection=True,
    check_direction_injection=True,
    check_pagination_bounds=True,
    valid_fields=valid_fields,
    valid_operators=valid_operators,
    valid_directions=valid_directions,
    max_page_size=100,
    max_page_number=1000,
)

query, parameters = CriteriaToPostgresqlConverter.convert(
    criteria=criteria,
    table='users',
    columns=['id', 'name', 'created_at'],
    check_table_injection=True,
    check_column_injection=True,
    check_criteria_injection=True,
    check_operator_injection=True,
    check_direction_injection=True,
    check_pagination_bounds=True,
    valid_tables=['users'],
    valid_columns=['id', 'name', 'created_at'],
    valid_operators=valid_operators,
    valid_directions=valid_directions,
    max_page_size=100,
    max_page_number=1000,
)

This keeps the public API flexible while ensuring SQL identifiers and query behavior are constrained by code you control.

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🛡️ SQL Conversion And Safety

Filter values are parameterized, which protects the values passed to predicates. Identifier validation is separate and must be enabled explicitly when identifiers can be influenced by users.

from criteria_pattern import Criteria, Direction, Filter, Operator, Order
from criteria_pattern.converters import CriteriaToPostgresqlConverter


criteria = Criteria(
    filters=[Filter(field='public_name', operator=Operator.CONTAINS, value='Doe')],
    orders=[Order(field='created_at', direction=Direction.DESC)],
    page_size=20,
    page_number=2,
)

query, parameters = CriteriaToPostgresqlConverter.convert(
    criteria=criteria,
    table='users',
    columns=['id', 'name', 'email'],
    columns_mapping={'public_name': 'name'},
    check_table_injection=True,
    check_column_injection=True,
    check_criteria_injection=True,
    check_operator_injection=True,
    check_direction_injection=True,
    check_pagination_bounds=True,
    valid_tables=['users'],
    valid_columns=['id', 'name', 'email', 'created_at', 'public_name'],
    valid_operators=[Operator.CONTAINS],
    valid_directions=[Direction.DESC],
    max_page_size=100,
    max_page_number=1000,
)

print(query)
print(parameters)
# >>> SELECT "id", "name", "email" FROM "users" WHERE "name" LIKE '%%' || %(parameter_0)s || '%%' ORDER BY "created_at" DESC LIMIT %(limit_1)s OFFSET %(offset_2)s;
# >>> {'parameter_0': 'Doe', 'limit_1': 20, 'offset_2': 20}

Use columns_mapping when your public API fields should not expose your database column names directly. When check_criteria_injection is enabled, include the accepted public criteria field names in valid_columns too.

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📦 Request Body Examples

Use BodyToCriteriaConverter when your API receives a decoded dictionary, for example from JSON.

from criteria_pattern import Direction, Operator
from criteria_pattern.converters import BodyToCriteriaConverter


body = {
    'filters': [
        {'field': 'full_name', 'operator': 'contains', 'value': 'Doe'},
        {'field': 'status', 'operator': 'IN', 'value': ['ACTIVE', 'PENDING']},
        {'field': 'price', 'operator': 'BETWEEN', 'value': [10, 100]},
    ],
    'orders': [
        {'field': 'created_at', 'direction': 'desc'},
    ],
    'page_size': 20,
    'page_number': 1,
}

criteria = BodyToCriteriaConverter.convert(
    body=body,
    fields_mapping={'full_name': 'name'},
    operator_mapping={'after': Operator.GREATER},
    check_field_injection=True,
    check_operator_injection=True,
    check_direction_injection=True,
    valid_fields=['name', 'status', 'price', 'created_at'],
    valid_operators=[Operator.CONTAINS, Operator.IN, Operator.BETWEEN],
    valid_directions=[Direction.DESC],
)

print(criteria.filters[0].field, criteria.filters[0].operator, criteria.filters[0].value)
# >>> name CONTAINS Doe

Accepted body keys are filters, orders, page_size and page_number. Unknown keys, missing required filter/order keys and invalid value shapes raise IntegrityError.

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🧭 Structured URL Query Examples

Use UrlToCriteriaConverter when you want an explicit URL format that can express filters, orders and pagination.

from criteria_pattern import Direction, Operator
from criteria_pattern.converters import UrlToCriteriaConverter


url = (
    'https://api.example.com/users?'
    'filters[0][field]=name&filters[0][operator]=CONTAINS&filters[0][value]=Doe&'
    'filters[1][field]=age&filters[1][operator]=GREATER_OR_EQUAL&filters[1][value]=18&'
    'orders[0][field]=created_at&orders[0][direction]=DESC&'
    'page_size=20&page_number=1'
)

criteria = UrlToCriteriaConverter.convert(
    url=url,
    valid_fields=['name', 'age', 'created_at'],
    valid_operators=[Operator.CONTAINS, Operator.GREATER_OR_EQUAL],
    valid_directions=[Direction.DESC],
)

print(criteria.filters[0].field, criteria.filters[0].operator, criteria.filters[0].value)
# >>> name CONTAINS Doe

print(criteria.orders[0].field, criteria.orders[0].direction)
# >>> created_at DESC

Structured URL values are converted to useful primitive types where possible: booleans, null / none, integers and floats.

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🎯 Real-Life Case: Multi-tenant User Search Service

Imagine an admin dashboard where each request must:

1. Always restrict results to the current tenant.
2. Optionally filter active users.
3. Search only users with company emails.
4. Sort by newest users first.

With Criteria Pattern, each concern is a small reusable criteria object. You combine them using & and |, then convert once to SQL:

from criteria_pattern import Criteria, Direction, Filter, Operator, Order
from criteria_pattern.converters import CriteriaToPostgresqlConverter


class UserSearchService:
    def __init__(self, tenant_id: str) -> None:
        self.tenant_id = tenant_id

    def build_query(self, *, only_active: bool, corporate_domain: str) -> tuple[str, dict[str, object]]:
        tenant_scope = Criteria(filters=[Filter(field='tenant_id', operator=Operator.EQUAL, value=self.tenant_id)])
        active_scope = Criteria(filters=[Filter(field='is_active', operator=Operator.EQUAL, value=True)])
        email_scope = Criteria(filters=[Filter(field='email', operator=Operator.ENDS_WITH, value=corporate_domain)])
        sort_scope = Criteria(orders=[Order(field='created_at', direction=Direction.DESC)])

        criteria = tenant_scope & email_scope & sort_scope
        if only_active:
            criteria = criteria & active_scope

        return CriteriaToPostgresqlConverter.convert(
            criteria=criteria,
            table='users',
            valid_columns=['tenant_id', 'is_active', 'email', 'created_at'],
            valid_operators=[Operator.EQUAL, Operator.ENDS_WITH],
            valid_directions=[Direction.DESC],
        )


service = UserSearchService(tenant_id='tenant_123')
query, parameters = service.build_query(only_active=True, corporate_domain='@acme.com')

print(query)
print(parameters)

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🔎 Simple URL Query Examples

Use SimpleUrlToCriteriaConverter when you want a compact public query format where each parameter becomes one AND filter. Plain parameters use equality, and suffixes map to operators.

from criteria_pattern import Operator
from criteria_pattern.converters import SimpleUrlToCriteriaConverter


criteria = SimpleUrlToCriteriaConverter.convert(
    url='https://api.example.com/users?name=Doe&age_gte=18&page_size=20&page_number=1',
    valid_fields=['name', 'age'],
    valid_operators=[Operator.EQUAL, Operator.GREATER_OR_EQUAL],
)

print(criteria.filters[0].field, criteria.filters[0].operator, criteria.filters[0].value)
# >>> name EQUAL Doe

print(criteria.filters[1].field, criteria.filters[1].operator, criteria.filters[1].value)
# >>> age GREATER_OR_EQUAL 18

print(criteria.page_size, criteria.page_number)
# >>> 20 1

Common suffixes:

URL parameter	Parsed filter
name=Doe	Filter(field='name', operator=Operator.EQUAL, value='Doe')
name_eq=Doe	Filter(field='name', operator=Operator.EQUAL, value='Doe')
status_ne=DELETED	Filter(field='status', operator=Operator.NOT_EQUAL, value='DELETED')
price_gt=10	Filter(field='price', operator=Operator.GREATER, value=10)
price_gte=10	Filter(field='price', operator=Operator.GREATER_OR_EQUAL, value=10)
price_lt=100	Filter(field='price', operator=Operator.LESS, value=100)
price_lte=100	Filter(field='price', operator=Operator.LESS_OR_EQUAL, value=100)
email_contains=gmail.com	Filter(field='email', operator=Operator.CONTAINS, value='gmail.com')
name_starts_with=Ad	Filter(field='name', operator=Operator.STARTS_WITH, value='Ad')
email_ends_with=.com	Filter(field='email', operator=Operator.ENDS_WITH, value='.com')
price_between=10,100	Filter(field='price', operator=Operator.BETWEEN, value=[10, 100])
age_not_between=18&age_not_between=30	Filter(field='age', operator=Operator.NOT_BETWEEN, value=[18, 30])
status_in=ACTIVE&status_in=PENDING	Filter(field='status', operator=Operator.IN, value=['ACTIVE', 'PENDING'])
status_not_in=DELETED	Filter(field='status', operator=Operator.NOT_IN, value=['DELETED'])
deleted_at_is_null=true	Filter(field='deleted_at', operator=Operator.IS_NULL, value=None)
deleted_at_is_not_null=true	Filter(field='deleted_at', operator=Operator.IS_NOT_NULL, value=None)

Comma-separated values are also supported for list operators:

criteria = SimpleUrlToCriteriaConverter.convert(
    url='https://api.example.com/users?status_in=ACTIVE,PENDING,BLOCKED',
    valid_fields=['status'],
    valid_operators=[Operator.IN],
)

print(criteria.filters[0].value)
# >>> ['ACTIVE', 'PENDING', 'BLOCKED']

You can map public field names to internal field names:

criteria = SimpleUrlToCriteriaConverter.convert(
    url='https://api.example.com/users?full_name_contains=Doe',
    fields_mapping={'full_name': 'name'},
    valid_fields=['name'],
    valid_operators=[Operator.CONTAINS],
)

print(criteria.filters[0].field, criteria.filters[0].operator, criteria.filters[0].value)
# >>> name CONTAINS Doe

You can also extend or override URL suffixes:

criteria = SimpleUrlToCriteriaConverter.convert(
    url='https://api.example.com/users?created_at_after=2026-05-18',
    suffix_operator_mapping={'after': Operator.GREATER},
    valid_fields=['created_at'],
    valid_operators=[Operator.GREATER],
)

print(criteria.filters[0].field, criteria.filters[0].operator, criteria.filters[0].value)
# >>> created_at GREATER 2026-05-18

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🧪 Testing Helpers

The package includes object mother helpers for tests in downstream projects. They are useful when you need valid random criteria objects and want to override only the fields that matter for a specific test.

from criteria_pattern import Filter, Operator
from criteria_pattern.models.testing.mothers import CriteriaMother
from criteria_pattern.models.testing.mothers.filter import FilterMother


criteria = CriteriaMother.with_filters(
    filters=[
        Filter(field='status', operator=Operator.EQUAL, value='ACTIVE'),
        FilterMother.create(field='age', operator=Operator.GREATER_OR_EQUAL, value=18),
    ]
)

print(criteria.has_filters())
# >>> True

Available helpers include CriteriaMother, FilterMother, FiltersMother, OrderMother, OrdersMother, PageSizeMother, PageNumberMother, plus field/operator/direction mothers under the filter and order testing packages.

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🤝 Contributing

We love community help! Before you open an issue or pull request, please read:

• 🤝 How to Contribute
• 🧭 Code of Conduct
• 🔐 Security Policy

Thank you for helping make 🤏🏻 Criteria Pattern package awesome! 🌟

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🔑 License

This project is licensed under the terms of the MIT license.

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