• Language: en
  • Documentation version: development

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

from django.db.models import Func, Transform, Value, fields
from django.db.models.functions import Coalesce


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

    def as_mysql(self, compiler, connection):
        # 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)"
        )

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


[docs]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:]))
[docs]class Length(Transform): """Return the number of characters in the expression.""" function = 'LENGTH' lookup_name = 'length' output_field = fields.IntegerField() def as_mysql(self, compiler, connection): return super().as_sql(compiler, connection, function='CHAR_LENGTH')
[docs]class Lower(Transform): function = 'LOWER' lookup_name = 'lower'
[docs]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 = fields.IntegerField() def as_postgresql(self, compiler, connection): return super().as_sql(compiler, connection, function='STRPOS')
[docs]class Substr(Func): function = 'SUBSTRING' 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): return super().as_sql(compiler, connection, function='SUBSTR') def as_oracle(self, compiler, connection): return super().as_sql(compiler, connection, function='SUBSTR')
[docs]class Upper(Transform): function = 'UPPER' lookup_name = 'upper'
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