# Django 3.2.12 documentation

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

    """Database functions that do comparisons or type conversions."""
    from django.db import NotSupportedError
    from django.db.models.expressions import Func, Value
    from django.db.models.fields.json import JSONField
    from django.utils.regex_helper import _lazy_re_compile

    class Cast(Func):
        """Coerce an expression to a new field type."""
        function = 'CAST'
        template = '%(function)s(%(expressions)s AS %(db_type)s)'

        def __init__(self, expression, output_field):
            super().__init__(expression, output_field=output_field)

        def as_sql(self, compiler, connection, **extra_context):
            extra_context['db_type'] = self.output_field.cast_db_type(connection)
            return super().as_sql(compiler, connection, **extra_context)

        def as_sqlite(self, compiler, connection, **extra_context):
            db_type = self.output_field.db_type(connection)
            if db_type in {'datetime', 'time'}:
                # Use strftime as datetime/time don't keep fractional seconds.
                template = 'strftime(%%s, %(expressions)s)'
                sql, params = super().as_sql(compiler, connection, template=template, **extra_context)
                format_string = '%H:%M:%f' if db_type == 'time' else '%Y-%m-%d %H:%M:%f'
                params.insert(0, format_string)
                return sql, params
            elif db_type == 'date':
                template = 'date(%(expressions)s)'
                return super().as_sql(compiler, connection, template=template, **extra_context)
            return self.as_sql(compiler, connection, **extra_context)

        def as_mysql(self, compiler, connection, **extra_context):
            template = None
            output_type = self.output_field.get_internal_type()
            # MySQL doesn't support explicit cast to float.
            if output_type == 'FloatField':
                template = '(%(expressions)s + 0.0)'
            # MariaDB doesn't support explicit cast to JSON.
            elif output_type == 'JSONField' and connection.mysql_is_mariadb:
                template = "JSON_EXTRACT(%(expressions)s, '$')"
            return self.as_sql(compiler, connection, template=template, **extra_context)

        def as_oracle(self, compiler, connection, **extra_context):
            if self.output_field.get_internal_type() == 'JSONField':
                # Oracle doesn't support explicit cast to JSON.
                template = "JSON_QUERY(%(expressions)s, '$')"
                return super().as_sql(compiler, connection, template=template, **extra_context)
            return self.as_sql(compiler, connection, **extra_context)

    class Coalesce(Func):
        """Return, from left to right, the first non-null expression."""
        function = 'COALESCE'

        def __init__(self, *expressions, **extra):
            if len(expressions) < 2:
                raise ValueError('Coalesce must take at least two expressions')
            super().__init__(*expressions, **extra)

        def as_oracle(self, compiler, connection, **extra_context):
            # Oracle prohibits mixing TextField (NCLOB) and CharField (NVARCHAR2),
            # so convert all fields to NCLOB when that type is expected.
            if self.output_field.get_internal_type() == 'TextField':
                clone = self.copy()
                clone.set_source_expressions([
                    Func(expression, function='TO_NCLOB') for expression in self.get_source_expressions()
                ])
                return super(Coalesce, clone).as_sql(compiler, connection, **extra_context)
            return self.as_sql(compiler, connection, **extra_context)

    class Collate(Func):
        function = 'COLLATE'
        template = '%(expressions)s %(function)s %(collation)s'
        # Inspired from https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
        collation_re = _lazy_re_compile(r'^[\w\-]+$')

        def __init__(self, expression, collation):
            if not (collation and self.collation_re.match(collation)):
                raise ValueError('Invalid collation name: %r.' % collation)
            self.collation = collation
            super().__init__(expression)

        def as_sql(self, compiler, connection, **extra_context):
            extra_context.setdefault('collation', connection.ops.quote_name(self.collation))
            return super().as_sql(compiler, connection, **extra_context)

    class Greatest(Func):
        """
        Return the maximum expression.

        If any expression is null the return value is database-specific:
        On PostgreSQL, the maximum not-null expression is returned.
        On MySQL, Oracle, and SQLite, if any expression is null, null is returned.
        """
        function = 'GREATEST'

        def __init__(self, *expressions, **extra):
            if len(expressions) < 2:
                raise ValueError('Greatest must take at least two expressions')
            super().__init__(*expressions, **extra)

        def as_sqlite(self, compiler, connection, **extra_context):
            """Use the MAX function on SQLite."""
            return super().as_sqlite(compiler, connection, function='MAX', **extra_context)

    class JSONObject(Func):
        function = 'JSON_OBJECT'
        output_field = JSONField()

        def __init__(self, **fields):
            expressions = []
            for key, value in fields.items():
                expressions.extend((Value(key), value))
            super().__init__(*expressions)

        def as_sql(self, compiler, connection, **extra_context):
            if not connection.features.has_json_object_function:
                raise NotSupportedError(
                    'JSONObject() is not supported on this database backend.'
                )
            return super().as_sql(compiler, connection, **extra_context)

        def as_postgresql(self, compiler, connection, **extra_context):
            return self.as_sql(
                compiler,
                connection,
                function='JSONB_BUILD_OBJECT',
                **extra_context,
            )

        def as_oracle(self, compiler, connection, **extra_context):
            class ArgJoiner:
                def join(self, args):
                    args = [' VALUE '.join(arg) for arg in zip(args[::2], args[1::2])]
                    return ', '.join(args)

            return self.as_sql(
                compiler,
                connection,
                arg_joiner=ArgJoiner(),
                template='%(function)s(%(expressions)s RETURNING CLOB)',
                **extra_context,
            )

    class Least(Func):
        """
        Return the minimum expression.

        If any expression is null the return value is database-specific:
        On PostgreSQL, return the minimum not-null expression.
        On MySQL, Oracle, and SQLite, if any expression is null, return null.
        """
        function = 'LEAST'

        def __init__(self, *expressions, **extra):
            if len(expressions) < 2:
                raise ValueError('Least must take at least two expressions')
            super().__init__(*expressions, **extra)

        def as_sqlite(self, compiler, connection, **extra_context):
            """Use the MIN function on SQLite."""
            return super().as_sqlite(compiler, connection, function='MIN', **extra_context)

    class NullIf(Func):
        function = 'NULLIF'
        arity = 2

        def as_oracle(self, compiler, connection, **extra_context):
            expression1 = self.get_source_expressions()[0]
            if isinstance(expression1, Value) and expression1.value is None:
                raise ValueError('Oracle does not allow Value(None) for expression1.')
            return super().as_sql(compiler, connection, **extra_context)