for performance only add a fromdbvalue method if the base field implements it remove the field name checks as they are not needed here assume we re deserializing don t wrap arrays that contains only none values psycopg doesn t allow this distinguish null and empty arrays in processrhs expects values to be hashable so convert lists to tuples for performance only add a from_db_value method if the base field implements it remove the field name checks as they are not needed here assume we re deserializing postgres uses 1 indexing don t add one here because postgres slices are weird don t wrap arrays that contains only none values psycopg doesn t allow this distinguish null and empty arrays in process_rhs expects values to be hashable so convert lists to tuples
import json

from django.contrib.postgres import lookups
from django.contrib.postgres.forms import SimpleArrayField
from django.contrib.postgres.validators import ArrayMaxLengthValidator
from django.core import checks, exceptions
from django.db.models import Field, Func, IntegerField, Transform, Value
from django.db.models.fields.mixins import CheckFieldDefaultMixin
from django.db.models.lookups import Exact, In
from django.utils.translation import gettext_lazy as _

from ..utils import prefix_validation_error
from .utils import AttributeSetter

__all__ = ["ArrayField"]


class ArrayField(CheckFieldDefaultMixin, Field):
    empty_strings_allowed = False
    default_error_messages = {
        "item_invalid": _("Item %(nth)s in the array did not validate:"),
        "nested_array_mismatch": _("Nested arrays must have the same length."),
    }
    _default_hint = ("list", "[]")

    def __init__(self, base_field, size=None, **kwargs):
        self.base_field = base_field
        self.db_collation = getattr(self.base_field, "db_collation", None)
        self.size = size
        if self.size:
            self.default_validators = [
                *self.default_validators,
                ArrayMaxLengthValidator(self.size),
            ]
        
        
        if hasattr(self.base_field, "from_db_value"):
            self.from_db_value = self._from_db_value
        super().__init__(**kwargs)

    @property
    def model(self):
        try:
            return self.__dict__["model"]
        except KeyError:
            raise AttributeError(
                "'%s' object has no attribute 'model'" % self.__class__.__name__
            )

    @model.setter
    def model(self, model):
        self.__dict__["model"] = model
        self.base_field.model = model

    @classmethod
    def _choices_is_value(cls, value):
        return isinstance(value, (list, tuple)) or super()._choices_is_value(value)

    def check(self, **kwargs):
        errors = super().check(**kwargs)
        if self.base_field.remote_field:
            errors.append(
                checks.Error(
                    "Base field for array cannot be a related field.",
                    obj=self,
                    id="postgres.E002",
                )
            )
        else:
            
            base_checks = self.base_field.check()
            if base_checks:
                error_messages = "\n    ".join(
                    "%s (%s)" % (base_check.msg, base_check.id)
                    for base_check in base_checks
                    if isinstance(base_check, checks.Error)
                )
                if error_messages:
                    errors.append(
                        checks.Error(
                            "Base field for array has errors:\n    %s" % error_messages,
                            obj=self,
                            id="postgres.E001",
                        )
                    )
                warning_messages = "\n    ".join(
                    "%s (%s)" % (base_check.msg, base_check.id)
                    for base_check in base_checks
                    if isinstance(base_check, checks.Warning)
                )
                if warning_messages:
                    errors.append(
                        checks.Warning(
                            "Base field for array has warnings:\n    %s"
                            % warning_messages,
                            obj=self,
                            id="postgres.W004",
                        )
                    )
        return errors

    def set_attributes_from_name(self, name):
        super().set_attributes_from_name(name)
        self.base_field.set_attributes_from_name(name)

    @property
    def description(self):
        return "Array of %s" % self.base_field.description

    def db_type(self, connection):
        size = self.size or ""
        return "%s[%s]" % (self.base_field.db_type(connection), size)

    def cast_db_type(self, connection):
        size = self.size or ""
        return "%s[%s]" % (self.base_field.cast_db_type(connection), size)

    def db_parameters(self, connection):
        db_params = super().db_parameters(connection)
        db_params["collation"] = self.db_collation
        return db_params

    def get_placeholder(self, value, compiler, connection):
        return "%s::{}".format(self.db_type(connection))

    def get_db_prep_value(self, value, connection, prepared=False):
        if isinstance(value, (list, tuple)):
            return [
                self.base_field.get_db_prep_value(i, connection, prepared=False)
                for i in value
            ]
        return value

    def deconstruct(self):
        name, path, args, kwargs = super().deconstruct()
        if path == "django.contrib.postgres.fields.array.ArrayField":
            path = "django.contrib.postgres.fields.ArrayField"
        kwargs.update(
            {
                "base_field": self.base_field.clone(),
                "size": self.size,
            }
        )
        return name, path, args, kwargs

    def to_python(self, value):
        if isinstance(value, str):
            
            vals = json.loads(value)
            value = [self.base_field.to_python(val) for val in vals]
        return value

    def _from_db_value(self, value, expression, connection):
        if value is None:
            return value
        return [
            self.base_field.from_db_value(item, expression, connection)
            for item in value
        ]

    def value_to_string(self, obj):
        values = []
        vals = self.value_from_object(obj)
        base_field = self.base_field

        for val in vals:
            if val is None:
                values.append(None)
            else:
                obj = AttributeSetter(base_field.attname, val)
                values.append(base_field.value_to_string(obj))
        return json.dumps(values)

    def get_transform(self, name):
        transform = super().get_transform(name)
        if transform:
            return transform
        if "_" not in name:
            try:
                index = int(name)
            except ValueError:
                pass
            else:
                index += 1  
                return IndexTransformFactory(index, self.base_field)
        try:
            start, end = name.split("_")
            start = int(start) + 1
            end = int(end)  
        except ValueError:
            pass
        else:
            return SliceTransformFactory(start, end)

    def validate(self, value, model_instance):
        super().validate(value, model_instance)
        for index, part in enumerate(value):
            try:
                self.base_field.validate(part, model_instance)
            except exceptions.ValidationError as error:
                raise prefix_validation_error(
                    error,
                    prefix=self.error_messages["item_invalid"],
                    code="item_invalid",
                    params={"nth": index + 1},
                )
        if isinstance(self.base_field, ArrayField):
            if len({len(i) for i in value}) > 1:
                raise exceptions.ValidationError(
                    self.error_messages["nested_array_mismatch"],
                    code="nested_array_mismatch",
                )

    def run_validators(self, value):
        super().run_validators(value)
        for index, part in enumerate(value):
            try:
                self.base_field.run_validators(part)
            except exceptions.ValidationError as error:
                raise prefix_validation_error(
                    error,
                    prefix=self.error_messages["item_invalid"],
                    code="item_invalid",
                    params={"nth": index + 1},
                )

    def formfield(self, **kwargs):
        return super().formfield(
            **{
                "form_class": SimpleArrayField,
                "base_field": self.base_field.formfield(),
                "max_length": self.size,
                **kwargs,
            }
        )


class ArrayRHSMixin:
    def __init__(self, lhs, rhs):
        
        
        if isinstance(rhs, (tuple, list)) and any(self._rhs_not_none_values(rhs)):
            expressions = []
            for value in rhs:
                if not hasattr(value, "resolve_expression"):
                    field = lhs.output_field
                    value = Value(field.base_field.get_prep_value(value))
                expressions.append(value)
            rhs = Func(
                *expressions,
                function="ARRAY",
                template="%(function)s[%(expressions)s]",
            )
        super().__init__(lhs, rhs)

    def process_rhs(self, compiler, connection):
        rhs, rhs_params = super().process_rhs(compiler, connection)
        cast_type = self.lhs.output_field.cast_db_type(connection)
        return "%s::%s" % (rhs, cast_type), rhs_params

    def _rhs_not_none_values(self, rhs):
        for x in rhs:
            if isinstance(x, (list, tuple)):
                yield from self._rhs_not_none_values(x)
            elif x is not None:
                yield True


@ArrayField.register_lookup
class ArrayContains(ArrayRHSMixin, lookups.DataContains):
    pass


@ArrayField.register_lookup
class ArrayContainedBy(ArrayRHSMixin, lookups.ContainedBy):
    pass


@ArrayField.register_lookup
class ArrayExact(ArrayRHSMixin, Exact):
    pass


@ArrayField.register_lookup
class ArrayOverlap(ArrayRHSMixin, lookups.Overlap):
    pass


@ArrayField.register_lookup
class ArrayLenTransform(Transform):
    lookup_name = "len"
    output_field = IntegerField()

    def as_sql(self, compiler, connection):
        lhs, params = compiler.compile(self.lhs)
        
        return (
            "CASE WHEN %(lhs)s IS NULL THEN NULL ELSE "
            "coalesce(array_length(%(lhs)s, 1), 0) END"
        ) % {"lhs": lhs}, params * 2


@ArrayField.register_lookup
class ArrayInLookup(In):
    def get_prep_lookup(self):
        values = super().get_prep_lookup()
        if hasattr(values, "resolve_expression"):
            return values
        
        
        prepared_values = []
        for value in values:
            if hasattr(value, "resolve_expression"):
                prepared_values.append(value)
            else:
                prepared_values.append(tuple(value))
        return prepared_values


class IndexTransform(Transform):
    def __init__(self, index, base_field, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.index = index
        self.base_field = base_field

    def as_sql(self, compiler, connection):
        lhs, params = compiler.compile(self.lhs)
        if not lhs.endswith("]"):
            lhs = "(%s)" % lhs
        return "%s[%%s]" % lhs, (*params, self.index)

    @property
    def output_field(self):
        return self.base_field


class IndexTransformFactory:
    def __init__(self, index, base_field):
        self.index = index
        self.base_field = base_field

    def __call__(self, *args, **kwargs):
        return IndexTransform(self.index, self.base_field, *args, **kwargs)


class SliceTransform(Transform):
    def __init__(self, start, end, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.start = start
        self.end = end

    def as_sql(self, compiler, connection):
        lhs, params = compiler.compile(self.lhs)
        if not lhs.endswith("]"):
            lhs = "(%s)" % lhs
        return "%s[%%s:%%s]" % lhs, (*params, self.start, self.end)


class SliceTransformFactory:
    def __init__(self, start, end):
        self.start = start
        self.end = end

    def __call__(self, *args, **kwargs):
        return SliceTransform(self.start, self.end, *args, **kwargs)