Class Coalesce

django/db/models/functions/comparison.py:70–101

Return, from left to right, the first non-null expression.

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)

    @property
    def empty_result_set_value(self):
        for expression in self.get_source_expressions():
            result = expression.empty_result_set_value
            if result is NotImplemented or result is not None:
                return result
        return None

    def as_oracle(self, compiler, connection, **extra_context):
        # Oracle prohibits mixing TextField, JSONField (NCLOB) and CharField
        # (NVARCHAR2), so convert all fields to NCLOB when that type is
        # expected.
        if self.output_field.get_internal_type() in ("TextField", "JSONField"):
            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):