# Django 4.2.11 documentation

# Source code for django.db.models.functions.text

    from django.db import NotSupportedError
    from django.db.models.expressions import Func, Value
    from django.db.models.fields import CharField, IntegerField, TextField
    from django.db.models.functions import Cast, Coalesce
    from django.db.models.lookups import Transform

    class MySQLSHA2Mixin:
        def as_mysql(self, compiler, connection, **extra_context):
            return super().as_sql(
                compiler,
                connection,
                template="SHA2(%%(expressions)s, %s)" % self.function[3:],
                **extra_context,
            )

    class OracleHashMixin:
        def as_oracle(self, compiler, connection, **extra_context):
            return super().as_sql(
                compiler,
                connection,
                template=(
                    "LOWER(RAWTOHEX(STANDARD_HASH(UTL_I18N.STRING_TO_RAW("
                    "%(expressions)s, 'AL32UTF8'), '%(function)s')))"
                ),
                **extra_context,
            )

    class PostgreSQLSHAMixin:
        def as_postgresql(self, compiler, connection, **extra_context):
            return super().as_sql(
                compiler,
                connection,
                template="ENCODE(DIGEST(%(expressions)s, '%(function)s'), 'hex')",
                function=self.function.lower(),
                **extra_context,
            )

    class Chr(Transform):
        function = "CHR"
        lookup_name = "chr"

        def as_mysql(self, compiler, connection, **extra_context):
            return super().as_sql(
                compiler,
                connection,
                function="CHAR",
                template="%(function)s(%(expressions)s USING utf16)",
                **extra_context,
            )

        def as_oracle(self, compiler, connection, **extra_context):
            return super().as_sql(
                compiler,
                connection,
                template="%(function)s(%(expressions)s USING NCHAR_CS)",
                **extra_context,
            )

        def as_sqlite(self, compiler, connection, **extra_context):
            return super().as_sql(compiler, connection, function="CHAR", **extra_context)

    class ConcatPair(Func):
        """
        Concatenate two arguments together. This is used by `Concat` because not
        all backend databases support more than two arguments.
        """

        function = "CONCAT"

        def as_sqlite(self, compiler, connection, **extra_context):
            coalesced = self.coalesce()
            return super(ConcatPair, coalesced).as_sql(
                compiler,
                connection,
                template="%(expressions)s",
                arg_joiner=" || ",
                **extra_context,
            )

        def as_postgresql(self, compiler, connection, **extra_context):
            copy = self.copy()
            copy.set_source_expressions(
                [
                    Cast(expression, TextField())
                    for expression in copy.get_source_expressions()
                ]
            )
            return super(ConcatPair, copy).as_sql(
                compiler,
                connection,
                **extra_context,
            )

        def as_mysql(self, compiler, connection, **extra_context):
            # Use CONCAT_WS with an empty separator so that NULLs are ignored.
            return super().as_sql(
                compiler,
                connection,
                function="CONCAT_WS",
                template="%(function)s('', %(expressions)s)",
                **extra_context,
            )

        def coalesce(self):
            # null on either side results in null for expression, wrap with coalesce
            c = self.copy()
            c.set_source_expressions(
                [
                    Coalesce(expression, Value(""))
                    for expression in c.get_source_expressions()
                ]
            )
            return c

    class Concat(Func):
        """
        Concatenate text fields together. Backends that result in an entire
        null expression when any arguments are null will wrap each argument in
        coalesce functions to ensure a non-null result.
        """

        function = None
        template = "%(expressions)s"

        def __init__(self, *expressions, **extra):
            if len(expressions) < 2:
                raise ValueError("Concat must take at least two expressions")
            paired = self._paired(expressions)
            super().__init__(paired, **extra)

        def _paired(self, expressions):
            # wrap pairs of expressions in successive concat functions
            # exp = [a, b, c, d]
            # -> ConcatPair(a, ConcatPair(b, ConcatPair(c, d))))
            if len(expressions) == 2:
                return ConcatPair(*expressions)
            return ConcatPair(expressions[0], self._paired(expressions[1:]))

    class Left(Func):
        function = "LEFT"
        arity = 2
        output_field = CharField()

        def __init__(self, expression, length, **extra):
            """
            expression: the name of a field, or an expression returning a string
            length: the number of characters to return from the start of the string
            """
            if not hasattr(length, "resolve_expression"):
                if length < 1:
                    raise ValueError("'length' must be greater than 0.")
            super().__init__(expression, length, **extra)

        def get_substr(self):
            return Substr(self.source_expressions[0], Value(1), self.source_expressions[1])

        def as_oracle(self, compiler, connection, **extra_context):
            return self.get_substr().as_oracle(compiler, connection, **extra_context)

        def as_sqlite(self, compiler, connection, **extra_context):
            return self.get_substr().as_sqlite(compiler, connection, **extra_context)

    class Length(Transform):
        """Return the number of characters in the expression."""

        function = "LENGTH"
        lookup_name = "length"
        output_field = IntegerField()

        def as_mysql(self, compiler, connection, **extra_context):
            return super().as_sql(
                compiler, connection, function="CHAR_LENGTH", **extra_context
            )

    class Lower(Transform):
        function = "LOWER"
        lookup_name = "lower"

    class LPad(Func):
        function = "LPAD"
        output_field = CharField()

        def __init__(self, expression, length, fill_text=Value(" "), **extra):
            if (
                not hasattr(length, "resolve_expression")
                and length is not None
                and length < 0
            ):
                raise ValueError("'length' must be greater or equal to 0.")
            super().__init__(expression, length, fill_text, **extra)

    class LTrim(Transform):
        function = "LTRIM"
        lookup_name = "ltrim"

    class MD5(OracleHashMixin, Transform):
        function = "MD5"
        lookup_name = "md5"

    class Ord(Transform):
        function = "ASCII"
        lookup_name = "ord"
        output_field = IntegerField()

        def as_mysql(self, compiler, connection, **extra_context):
            return super().as_sql(compiler, connection, function="ORD", **extra_context)

        def as_sqlite(self, compiler, connection, **extra_context):
            return super().as_sql(compiler, connection, function="UNICODE", **extra_context)

    class Repeat(Func):
        function = "REPEAT"
        output_field = CharField()

        def __init__(self, expression, number, **extra):
            if (
                not hasattr(number, "resolve_expression")
                and number is not None
                and number < 0
            ):
                raise ValueError("'number' must be greater or equal to 0.")
            super().__init__(expression, number, **extra)

        def as_oracle(self, compiler, connection, **extra_context):
            expression, number = self.source_expressions
            length = None if number is None else Length(expression) * number
            rpad = RPad(expression, length, expression)
            return rpad.as_sql(compiler, connection, **extra_context)

    class Replace(Func):
        function = "REPLACE"

        def __init__(self, expression, text, replacement=Value(""), **extra):
            super().__init__(expression, text, replacement, **extra)

    class Reverse(Transform):
        function = "REVERSE"
        lookup_name = "reverse"

        def as_oracle(self, compiler, connection, **extra_context):
            # REVERSE in Oracle is undocumented and doesn't support multi-byte
            # strings. Use a special subquery instead.
            return super().as_sql(
                compiler,
                connection,
                template=(
                    "(SELECT LISTAGG(s) WITHIN GROUP (ORDER BY n DESC) FROM "
                    "(SELECT LEVEL n, SUBSTR(%(expressions)s, LEVEL, 1) s "
                    "FROM DUAL CONNECT BY LEVEL <= LENGTH(%(expressions)s)) "
                    "GROUP BY %(expressions)s)"
                ),
                **extra_context,
            )

    class Right(Left):
        function = "RIGHT"

        def get_substr(self):
            return Substr(
                self.source_expressions[0], self.source_expressions[1] * Value(-1)
            )

    class RPad(LPad):
        function = "RPAD"

    class RTrim(Transform):
        function = "RTRIM"
        lookup_name = "rtrim"

    class SHA1(OracleHashMixin, PostgreSQLSHAMixin, Transform):
        function = "SHA1"
        lookup_name = "sha1"

    class SHA224(MySQLSHA2Mixin, PostgreSQLSHAMixin, Transform):
        function = "SHA224"
        lookup_name = "sha224"

        def as_oracle(self, compiler, connection, **extra_context):
            raise NotSupportedError("SHA224 is not supported on Oracle.")

    class SHA256(MySQLSHA2Mixin, OracleHashMixin, PostgreSQLSHAMixin, Transform):
        function = "SHA256"
        lookup_name = "sha256"

    class SHA384(MySQLSHA2Mixin, OracleHashMixin, PostgreSQLSHAMixin, Transform):
        function = "SHA384"
        lookup_name = "sha384"

    class SHA512(MySQLSHA2Mixin, OracleHashMixin, PostgreSQLSHAMixin, Transform):
        function = "SHA512"
        lookup_name = "sha512"

    class StrIndex(Func):
        """
        Return a positive integer corresponding to the 1-indexed position of the
        first occurrence of a substring inside another string, or 0 if the
        substring is not found.
        """

        function = "INSTR"
        arity = 2
        output_field = IntegerField()

        def as_postgresql(self, compiler, connection, **extra_context):
            return super().as_sql(compiler, connection, function="STRPOS", **extra_context)

    class Substr(Func):
        function = "SUBSTRING"
        output_field = CharField()

        def __init__(self, expression, pos, length=None, **extra):
            """
            expression: the name of a field, or an expression returning a string
            pos: an integer > 0, or an expression returning an integer
            length: an optional number of characters to return
            """
            if not hasattr(pos, "resolve_expression"):
                if pos < 1:
                    raise ValueError("'pos' must be greater than 0")
            expressions = [expression, pos]
            if length is not None:
                expressions.append(length)
            super().__init__(*expressions, **extra)

        def as_sqlite(self, compiler, connection, **extra_context):
            return super().as_sql(compiler, connection, function="SUBSTR", **extra_context)

        def as_oracle(self, compiler, connection, **extra_context):
            return super().as_sql(compiler, connection, function="SUBSTR", **extra_context)

    class Trim(Transform):
        function = "TRIM"
        lookup_name = "trim"

    class Upper(Transform):
        function = "UPPER"
        lookup_name = "upper"