• Language: en
  • 2.1
  • Documentation version: development

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

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


class BytesToCharFieldConversionMixin:
    """
    Convert CharField results from bytes to str.

    MySQL returns long data types (bytes) instead of chars when it can't
    determine the length of the result string. For example:
        LPAD(column1, CHAR_LENGTH(column2), ' ')
    returns the LONGTEXT (bytes) instead of VARCHAR.
    """
    def convert_value(self, value, expression, connection):
        if connection.features.db_functions_convert_bytes_to_str:
            if self.output_field.get_internal_type() == 'CharField' and isinstance(value, bytes):
                return value.decode()
        return super().convert_value(value, expression, connection)


[docs]class Chr(Transform): function = 'CHR' lookup_name = 'chr' def as_mysql(self, compiler, connection, **extra_context): return super().as_sql( compiler, connection, function='CHAR', template='%(function)s(%(expressions)s USING utf16)', **extra_context ) def as_oracle(self, compiler, connection, **extra_context): return super().as_sql( compiler, connection, template='%(function)s(%(expressions)s USING NCHAR_CS)', **extra_context ) def as_sqlite(self, compiler, connection, **extra_context): return super().as_sql(compiler, connection, function='CHAR', **extra_context)
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, **extra_context): coalesced = self.coalesce() return super(ConcatPair, coalesced).as_sql( compiler, connection, template='%(expressions)s', arg_joiner=' || ', **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() 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 Left(Func): function = 'LEFT' arity = 2 def __init__(self, expression, length, **extra): """ expression: the name of a field, or an expression returning a string length: the number of characters to return from the start of the string """ if not hasattr(length, 'resolve_expression'): if length < 1: raise ValueError("'length' must be greater than 0.") super().__init__(expression, length, **extra) def get_substr(self): return Substr(self.source_expressions[0], Value(1), self.source_expressions[1]) def use_substr(self, compiler, connection, **extra_context): return self.get_substr().as_oracle(compiler, connection, **extra_context) as_oracle = use_substr as_sqlite = use_substr
[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, **extra_context): return super().as_sql(compiler, connection, function='CHAR_LENGTH', **extra_context)
[docs]class Lower(Transform): function = 'LOWER' lookup_name = 'lower'
[docs]class LPad(BytesToCharFieldConversionMixin, Func): function = 'LPAD' def __init__(self, expression, length, fill_text=Value(' '), **extra): if not hasattr(length, 'resolve_expression') and length is not None and length < 0: raise ValueError("'length' must be greater or equal to 0.") super().__init__(expression, length, fill_text, **extra)
[docs]class LTrim(Transform): function = 'LTRIM' lookup_name = 'ltrim'
[docs]class Ord(Transform): function = 'ASCII' lookup_name = 'ord' output_field = IntegerField() def as_mysql(self, compiler, connection, **extra_context): return super().as_sql(compiler, connection, function='ORD', **extra_context) def as_sqlite(self, compiler, connection, **extra_context): return super().as_sql(compiler, connection, function='UNICODE', **extra_context)
[docs]class Repeat(BytesToCharFieldConversionMixin, Func): function = 'REPEAT' def __init__(self, expression, number, **extra): if not hasattr(number, 'resolve_expression') and number is not None and number < 0: raise ValueError("'number' must be greater or equal to 0.") super().__init__(expression, number, **extra) def as_oracle(self, compiler, connection, **extra_context): expression, number = self.source_expressions length = None if number is None else Length(expression) * number rpad = RPad(expression, length, expression) return rpad.as_sql(compiler, connection, **extra_context)
[docs]class Replace(Func): function = 'REPLACE' def __init__(self, expression, text, replacement=Value(''), **extra): super().__init__(expression, text, replacement, **extra)
[docs]class RPad(LPad): function = 'RPAD'
[docs]class RTrim(Transform): function = 'RTRIM' lookup_name = 'rtrim'
[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, **extra_context): return super().as_sql(compiler, connection, function='STRPOS', **extra_context)
[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, **extra_context): return super().as_sql(compiler, connection, function='SUBSTR', **extra_context) def as_oracle(self, compiler, connection, **extra_context): return super().as_sql(compiler, connection, function='SUBSTR', **extra_context)
[docs]class Trim(Transform): function = 'TRIM' lookup_name = 'trim'
[docs]class Upper(Transform): function = 'UPPER' lookup_name = 'upper'
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