# Django 2.2.9.dev20191202104323 文档

# django.contrib.postgres.fields.array 源代码

    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, IntegerField, Transform
    from django.db.models.lookups import Exact, In
    from django.utils.inspect import func_supports_parameter
    from django.utils.translation import gettext_lazy as _

    from ..utils import prefix_validation_error
    from .mixins import CheckFieldDefaultMixin
    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.size = size
            if self.size:
                self.default_validators = [*self.default_validators, ArrayMaxLengthValidator(self.size)]
            # For performance, only add a from_db_value() method if the base field
            # implements it.
            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

        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:
                # Remove the field name checks as they are not needed here.
                base_errors = self.base_field.check()
                if base_errors:
                    messages = '\n    '.join('%s (%s)' % (error.msg, error.id) for error in base_errors)
                    errors.append(
                        checks.Error(
                            'Base field for array has errors:\n    %s' % messages,
                            obj=self,
                            id='postgres.E001'
                        )
                    )
            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 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):
                # Assume we're deserializing
                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, {})
                if func_supports_parameter(self.base_field.from_db_value, 'context')  # RemovedInDjango30Warning
                else 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  # postgres uses 1-indexing
                    return IndexTransformFactory(index, self.base_field)
            try:
                start, end = name.split('_')
                start = int(start) + 1
                end = int(end)  # don't add one here because postgres slices are weird
            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,
            })

    @ArrayField.register_lookup
    class ArrayContains(lookups.DataContains):
        def as_sql(self, qn, connection):
            sql, params = super().as_sql(qn, connection)
            sql = '%s::%s' % (sql, self.lhs.output_field.db_type(connection))
            return sql, params

    @ArrayField.register_lookup
    class ArrayContainedBy(lookups.ContainedBy):
        def as_sql(self, qn, connection):
            sql, params = super().as_sql(qn, connection)
            sql = '%s::%s' % (sql, self.lhs.output_field.db_type(connection))
            return sql, params

    @ArrayField.register_lookup
    class ArrayExact(Exact):
        def as_sql(self, qn, connection):
            sql, params = super().as_sql(qn, connection)
            sql = '%s::%s' % (sql, self.lhs.output_field.db_type(connection))
            return sql, params

    @ArrayField.register_lookup
    class ArrayOverlap(lookups.Overlap):
        def as_sql(self, qn, connection):
            sql, params = super().as_sql(qn, connection)
            sql = '%s::%s' % (sql, self.lhs.output_field.db_type(connection))
            return sql, params

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

        def as_sql(self, compiler, connection):
            lhs, params = compiler.compile(self.lhs)
            # Distinguish NULL and empty arrays
            return (
                'CASE WHEN %(lhs)s IS NULL THEN NULL ELSE '
                'coalesce(array_length(%(lhs)s, 1), 0) END'
            ) % {'lhs': lhs}, params

    @ArrayField.register_lookup
    class ArrayInLookup(In):
        def get_prep_lookup(self):
            values = super().get_prep_lookup()
            if hasattr(self.rhs, '_prepare'):
                # Subqueries don't need further preparation.
                return values
            # In.process_rhs() expects values to be hashable, so convert lists
            # to tuples.
            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)
            return '%s[%s]' % (lhs, self.index), params

        @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)
            return '%s[%s:%s]' % (lhs, self.start, self.end), params

    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)