Add contrib module with utilities that have been helpful over the years

Author: Photonios

psqlextra/contrib/README.md

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+# psqlextra.contrib
+
+This module contains a arbitrary collection of utilities and snippets that build on top of core functionality provided by django-postgres-extra.
+
+This collection is UNTESTED, UNSUPPORTED and UNDOCUMENTED. They are only provided here as an inspiration. Use at your own risk.

psqlextra/contrib/__init__.py

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+from .model_data_migrator import PostgresModelDataMigrator
+from .static_row import StaticRowQueryCompiler, StaticRowQuerySet
+from .transaction import no_transaction
+
+__all__ = [
+    "PostgresModelDataMigrator",
+    "PostgresModelDataMigratorState" "StaticRowQuery",
+    "StaticRowQueryCompiler",
+    "StaticRowQuerySet",
+    "no_transaction",
+]

psqlextra/contrib/expressions.py

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+from django.db import models
+from django.db.models.expressions import CombinedExpression, Func
+
+
+class Equals(CombinedExpression):
+    """Expression that constructs `{lhs} = {rhs}`.
+
+    Used as an alternative to Django's `Q` object when the
+    left-hand side is a aliased field not known to Django.
+    """
+
+    connector: str = "="
+
+    def __init__(self, lhs, rhs) -> None:
+        super().__init__(
+            lhs, self.connector, rhs, output_field=models.BooleanField()
+        )
+
+
+class Is(Equals):
+    """Expression that constructs `{lhs} IS {rhs}`."""
+
+    connector: str = "IS"
+
+
+class GreaterThen(Equals):
+    """Expression that constructs `{lhs} > {rhs}`."""
+
+    connector: str = ">"
+
+
+class LowerThenOrEqual(Equals):
+    """Expression that constructs `{lhs} <= {rhs}`."""
+
+    connector: str = "<="
+
+
+class And(Equals):
+    """Expression that constructs `{lhs} AND {rhs}`."""
+
+    connector: str = "AND"
+
+
+class Bool(Func):
+    """Cast to a boolean."""
+
+    function = "BOOL"