# Django 4.2.11 documentation

# Source code for django.db.models.indexes

    from django.db.backends.utils import names_digest, split_identifier
    from django.db.models.expressions import Col, ExpressionList, F, Func, OrderBy
    from django.db.models.functions import Collate
    from django.db.models.query_utils import Q
    from django.db.models.sql import Query
    from django.utils.functional import partition

    __all__ = ["Index"]

    class Index:
        suffix = "idx"
        # The max length of the name of the index (restricted to 30 for
        # cross-database compatibility with Oracle)
        max_name_length = 30

        def __init__(
            self,
            *expressions,
            fields=(),
            name=None,
            db_tablespace=None,
            opclasses=(),
            condition=None,
            include=None,
        ):
            if opclasses and not name:
                raise ValueError("An index must be named to use opclasses.")
            if not isinstance(condition, (type(None), Q)):
                raise ValueError("Index.condition must be a Q instance.")
            if condition and not name:
                raise ValueError("An index must be named to use condition.")
            if not isinstance(fields, (list, tuple)):
                raise ValueError("Index.fields must be a list or tuple.")
            if not isinstance(opclasses, (list, tuple)):
                raise ValueError("Index.opclasses must be a list or tuple.")
            if not expressions and not fields:
                raise ValueError(
                    "At least one field or expression is required to define an index."
                )
            if expressions and fields:
                raise ValueError(
                    "Index.fields and expressions are mutually exclusive.",
                )
            if expressions and not name:
                raise ValueError("An index must be named to use expressions.")
            if expressions and opclasses:
                raise ValueError(
                    "Index.opclasses cannot be used with expressions. Use "
                    "django.contrib.postgres.indexes.OpClass() instead."
                )
            if opclasses and len(fields) != len(opclasses):
                raise ValueError(
                    "Index.fields and Index.opclasses must have the same number of "
                    "elements."
                )
            if fields and not all(isinstance(field, str) for field in fields):
                raise ValueError("Index.fields must contain only strings with field names.")
            if include and not name:
                raise ValueError("A covering index must be named.")
            if not isinstance(include, (type(None), list, tuple)):
                raise ValueError("Index.include must be a list or tuple.")
            self.fields = list(fields)
            # A list of 2-tuple with the field name and ordering ('' or 'DESC').
            self.fields_orders = [
                (field_name[1:], "DESC") if field_name.startswith("-") else (field_name, "")
                for field_name in self.fields
            ]
            self.name = name or ""
            self.db_tablespace = db_tablespace
            self.opclasses = opclasses
            self.condition = condition
            self.include = tuple(include) if include else ()
            self.expressions = tuple(
                F(expression) if isinstance(expression, str) else expression
                for expression in expressions
            )

        @property
        def contains_expressions(self):
            return bool(self.expressions)

        def _get_condition_sql(self, model, schema_editor):
            if self.condition is None:
                return None
            query = Query(model=model, alias_cols=False)
            where = query.build_where(self.condition)
            compiler = query.get_compiler(connection=schema_editor.connection)
            sql, params = where.as_sql(compiler, schema_editor.connection)
            return sql % tuple(schema_editor.quote_value(p) for p in params)

        def create_sql(self, model, schema_editor, using="", **kwargs):
            include = [
                model._meta.get_field(field_name).column for field_name in self.include
            ]
            condition = self._get_condition_sql(model, schema_editor)
            if self.expressions:
                index_expressions = []
                for expression in self.expressions:
                    index_expression = IndexExpression(expression)
                    index_expression.set_wrapper_classes(schema_editor.connection)
                    index_expressions.append(index_expression)
                expressions = ExpressionList(*index_expressions).resolve_expression(
                    Query(model, alias_cols=False),
                )
                fields = None
                col_suffixes = None
            else:
                fields = [
                    model._meta.get_field(field_name)
                    for field_name, _ in self.fields_orders
                ]
                if schema_editor.connection.features.supports_index_column_ordering:
                    col_suffixes = [order[1] for order in self.fields_orders]
                else:
                    col_suffixes = [""] * len(self.fields_orders)
                expressions = None
            return schema_editor._create_index_sql(
                model,
                fields=fields,
                name=self.name,
                using=using,
                db_tablespace=self.db_tablespace,
                col_suffixes=col_suffixes,
                opclasses=self.opclasses,
                condition=condition,
                include=include,
                expressions=expressions,
                **kwargs,
            )

        def remove_sql(self, model, schema_editor, **kwargs):
            return schema_editor._delete_index_sql(model, self.name, **kwargs)

        def deconstruct(self):
            path = "%s.%s" % (self.__class__.__module__, self.__class__.__name__)
            path = path.replace("django.db.models.indexes", "django.db.models")
            kwargs = {"name": self.name}
            if self.fields:
                kwargs["fields"] = self.fields
            if self.db_tablespace is not None:
                kwargs["db_tablespace"] = self.db_tablespace
            if self.opclasses:
                kwargs["opclasses"] = self.opclasses
            if self.condition:
                kwargs["condition"] = self.condition
            if self.include:
                kwargs["include"] = self.include
            return (path, self.expressions, kwargs)

        def clone(self):
            """Create a copy of this Index."""
            _, args, kwargs = self.deconstruct()
            return self.__class__(*args, **kwargs)

        def set_name_with_model(self, model):
            """
            Generate a unique name for the index.

            The name is divided into 3 parts - table name (12 chars), field name
            (8 chars) and unique hash + suffix (10 chars). Each part is made to
            fit its size by truncating the excess length.
            """
            _, table_name = split_identifier(model._meta.db_table)
            column_names = [
                model._meta.get_field(field_name).column
                for field_name, order in self.fields_orders
            ]
            column_names_with_order = [
                (("-%s" if order else "%s") % column_name)
                for column_name, (field_name, order) in zip(
                    column_names, self.fields_orders
                )
            ]
            # The length of the parts of the name is based on the default max
            # length of 30 characters.
            hash_data = [table_name] + column_names_with_order + [self.suffix]
            self.name = "%s_%s_%s" % (
                table_name[:11],
                column_names[0][:7],
                "%s_%s" % (names_digest(*hash_data, length=6), self.suffix),
            )
            if len(self.name) > self.max_name_length:
                raise ValueError(
                    "Index too long for multiple database support. Is self.suffix "
                    "longer than 3 characters?"
                )
            if self.name[0] == "_" or self.name[0].isdigit():
                self.name = "D%s" % self.name[1:]

        def __repr__(self):
            return "<%s:%s%s%s%s%s%s%s>" % (
                self.__class__.__qualname__,
                "" if not self.fields else " fields=%s" % repr(self.fields),
                "" if not self.expressions else " expressions=%s" % repr(self.expressions),
                "" if not self.name else " name=%s" % repr(self.name),
                ""
                if self.db_tablespace is None
                else " db_tablespace=%s" % repr(self.db_tablespace),
                "" if self.condition is None else " condition=%s" % self.condition,
                "" if not self.include else " include=%s" % repr(self.include),
                "" if not self.opclasses else " opclasses=%s" % repr(self.opclasses),
            )

        def __eq__(self, other):
            if self.__class__ == other.__class__:
                return self.deconstruct() == other.deconstruct()
            return NotImplemented

    class IndexExpression(Func):
        """Order and wrap expressions for CREATE INDEX statements."""

        template = "%(expressions)s"
        wrapper_classes = (OrderBy, Collate)

        def set_wrapper_classes(self, connection=None):
            # Some databases (e.g. MySQL) treats COLLATE as an indexed expression.
            if connection and connection.features.collate_as_index_expression:
                self.wrapper_classes = tuple(
                    [
                        wrapper_cls
                        for wrapper_cls in self.wrapper_classes
                        if wrapper_cls is not Collate
                    ]
                )

        @classmethod
        def register_wrappers(cls, *wrapper_classes):
            cls.wrapper_classes = wrapper_classes

        def resolve_expression(
            self,
            query=None,
            allow_joins=True,
            reuse=None,
            summarize=False,
            for_save=False,
        ):
            expressions = list(self.flatten())
            # Split expressions and wrappers.
            index_expressions, wrappers = partition(
                lambda e: isinstance(e, self.wrapper_classes),
                expressions,
            )
            wrapper_types = [type(wrapper) for wrapper in wrappers]
            if len(wrapper_types) != len(set(wrapper_types)):
                raise ValueError(
                    "Multiple references to %s can't be used in an indexed "
                    "expression."
                    % ", ".join(
                        [wrapper_cls.__qualname__ for wrapper_cls in self.wrapper_classes]
                    )
                )
            if expressions[1 : len(wrappers) + 1] != wrappers:
                raise ValueError(
                    "%s must be topmost expressions in an indexed expression."
                    % ", ".join(
                        [wrapper_cls.__qualname__ for wrapper_cls in self.wrapper_classes]
                    )
                )
            # Wrap expressions in parentheses if they are not column references.
            root_expression = index_expressions[1]
            resolve_root_expression = root_expression.resolve_expression(
                query,
                allow_joins,
                reuse,
                summarize,
                for_save,
            )
            if not isinstance(resolve_root_expression, Col):
                root_expression = Func(root_expression, template="(%(expressions)s)")

            if wrappers:
                # Order wrappers and set their expressions.
                wrappers = sorted(
                    wrappers,
                    key=lambda w: self.wrapper_classes.index(type(w)),
                )
                wrappers = [wrapper.copy() for wrapper in wrappers]
                for i, wrapper in enumerate(wrappers[:-1]):
                    wrapper.set_source_expressions([wrappers[i + 1]])
                # Set the root expression on the deepest wrapper.
                wrappers[-1].set_source_expressions([root_expression])
                self.set_source_expressions([wrappers[0]])
            else:
                # Use the root expression, if there are no wrappers.
                self.set_source_expressions([root_expression])
            return super().resolve_expression(
                query, allow_joins, reuse, summarize, for_save
            )

        def as_sqlite(self, compiler, connection, **extra_context):
            # Casting to numeric is unnecessary.
            return self.as_sql(compiler, connection, **extra_context)