Class ConcatPair

django/db/models/functions/text.py:68–122

Concatenate two arguments together. This is used by `Concat` because not all backend databases support more than two arguments.

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

    as_sqlite = pipes_concat_sql

    def as_postgresql(self, compiler, connection, **extra_context):
        c = self.copy()
        c.set_source_expressions(
            [
                (
                    expression
                    if isinstance(expression.output_field, (CharField, TextField))
                    else Cast(expression, TextField())
                )
                for expression in c.get_source_expressions()
            ]
        )
        return c.pipes_concat_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):