Class Cast

django/db/models/functions/comparison.py:7–67

Coerce an expression to a new field type.

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 = (format_string, *params)
            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_postgresql(self, compiler, connection, **extra_context):
        # CAST would be valid too, but the :: shortcut syntax is more readable.
        # 'expressions' is wrapped in parentheses in case it's a complex
        # expression.
        return self.as_sql(
            compiler,
            connection,
            template="(%(expressions)s)::%(db_type)s",
            **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(