• 1.8
  • dev
  • Documentation version: 1.9

Source code for django.db.models.functions

"""
Classes that represent database functions.
"""
from django.db.models import (
    DateTimeField, Func, IntegerField, Transform, Value,
)


[docs]class Coalesce(Func): """ Chooses, from left to right, the first non-null expression and returns it. """ function = 'COALESCE' def __init__(self, *expressions, **extra): if len(expressions) < 2: raise ValueError('Coalesce must take at least two expressions') super(Coalesce, self).__init__(*expressions, **extra) def as_oracle(self, compiler, connection): # we can't mix TextField (NCLOB) and CharField (NVARCHAR), so convert # all fields to NCLOB when we expect NCLOB if self.output_field.get_internal_type() == 'TextField': class ToNCLOB(Func): function = 'TO_NCLOB' expressions = [ ToNCLOB(expression) for expression in self.get_source_expressions()] self.set_source_expressions(expressions) return super(Coalesce, self).as_sql(compiler, connection)
class ConcatPair(Func): """ A helper class that concatenates two arguments together. This is used by `Concat` because not all backend databases support more than two arguments. """ function = 'CONCAT' def __init__(self, left, right, **extra): super(ConcatPair, self).__init__(left, right, **extra) def as_sqlite(self, compiler, connection): coalesced = self.coalesce() coalesced.arg_joiner = ' || ' coalesced.template = '%(expressions)s' return super(ConcatPair, coalesced).as_sql(compiler, connection) def as_mysql(self, compiler, connection): # Use CONCAT_WS with an empty separator so that NULLs are ignored. self.function = 'CONCAT_WS' self.template = "%(function)s('', %(expressions)s)" return super(ConcatPair, self).as_sql(compiler, connection) 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): """ Concatenates 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 we always get 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(Concat, self).__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 Greatest(Func): """ Chooses the maximum expression and returns it. If any expression is null the return value is database-specific: On Postgres, the maximum not-null expression is returned. On MySQL, Oracle, and SQLite, if any expression is null, null is returned. """ function = 'GREATEST' def __init__(self, *expressions, **extra): if len(expressions) < 2: raise ValueError('Greatest must take at least two expressions') super(Greatest, self).__init__(*expressions, **extra) def as_sqlite(self, compiler, connection): """Use the MAX function on SQLite.""" return super(Greatest, self).as_sql(compiler, connection, function='MAX')
[docs]class Least(Func): """ Chooses the minimum expression and returns it. If any expression is null the return value is database-specific: On Postgres, the minimum not-null expression is returned. On MySQL, Oracle, and SQLite, if any expression is null, null is returned. """ function = 'LEAST' def __init__(self, *expressions, **extra): if len(expressions) < 2: raise ValueError('Least must take at least two expressions') super(Least, self).__init__(*expressions, **extra) def as_sqlite(self, compiler, connection): """Use the MIN function on SQLite.""" return super(Least, self).as_sql(compiler, connection, function='MIN')
[docs]class Length(Transform): """Returns the number of characters in the expression""" function = 'LENGTH' lookup_name = 'length' def __init__(self, expression, **extra): output_field = extra.pop('output_field', IntegerField()) super(Length, self).__init__(expression, output_field=output_field, **extra) def as_mysql(self, compiler, connection): self.function = 'CHAR_LENGTH' return super(Length, self).as_sql(compiler, connection)
[docs]class Lower(Transform): function = 'LOWER' lookup_name = 'lower' def __init__(self, expression, **extra): super(Lower, self).__init__(expression, **extra)
[docs]class Now(Func): template = 'CURRENT_TIMESTAMP' def __init__(self, output_field=None, **extra): if output_field is None: output_field = DateTimeField() super(Now, self).__init__(output_field=output_field, **extra) def as_postgresql(self, compiler, connection): # Postgres' CURRENT_TIMESTAMP means "the time at the start of the # transaction". We use STATEMENT_TIMESTAMP to be cross-compatible with # other databases. self.template = 'STATEMENT_TIMESTAMP()' return self.as_sql(compiler, connection)
[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") pos = Value(pos) expressions = [expression, pos] if length is not None: if not hasattr(length, 'resolve_expression'): length = Value(length) expressions.append(length) super(Substr, self).__init__(*expressions, **extra) def as_sqlite(self, compiler, connection): self.function = 'SUBSTR' return super(Substr, self).as_sql(compiler, connection) def as_oracle(self, compiler, connection): self.function = 'SUBSTR' return super(Substr, self).as_sql(compiler, connection)
[docs]class Upper(Transform): function = 'UPPER' lookup_name = 'upper' def __init__(self, expression, **extra): super(Upper, self).__init__(expression, **extra)
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