Kod źródłowy modułu django.db.models.functions.base

"""
Classes that represent database functions.
"""
from django.db.models import Func, Transform, Value, fields


[dokumenty]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_postgresql(self, compiler, connection): # CAST would be valid too, but the :: shortcut syntax is more readable. return self.as_sql(compiler, connection, template='%(expressions)s::%(db_type)s')
[dokumenty]class Coalesce(Func): """Return, from left to right, the first non-null expression.""" function = 'COALESCE' def __init__(self, *expressions, **extra): if len(expressions) < 2: raise ValueError('Coalesce must take at least two expressions') super().__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()] clone = self.copy() clone.set_source_expressions(expressions) return super(Coalesce, clone).as_sql(compiler, connection) return self.as_sql(compiler, connection)
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
[dokumenty]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:]))
[dokumenty]class Greatest(Func): """ Return the maximum expression. 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().__init__(*expressions, **extra) def as_sqlite(self, compiler, connection): """Use the MAX function on SQLite.""" return super().as_sqlite(compiler, connection, function='MAX')
[dokumenty]class Least(Func): """ Return the minimum expression. If any expression is null the return value is database-specific: On Postgres, return the minimum not-null expression. On MySQL, Oracle, and SQLite, if any expression is null, return null. """ function = 'LEAST' def __init__(self, *expressions, **extra): if len(expressions) < 2: raise ValueError('Least must take at least two expressions') super().__init__(*expressions, **extra) def as_sqlite(self, compiler, connection): """Use the MIN function on SQLite.""" return super().as_sqlite(compiler, connection, function='MIN')
[dokumenty]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')
[dokumenty]class Lower(Transform): function = 'LOWER' lookup_name = 'lower'
[dokumenty]class Now(Func): template = 'CURRENT_TIMESTAMP' output_field = fields.DateTimeField() 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. return self.as_sql(compiler, connection, template='STATEMENT_TIMESTAMP()')
[dokumenty]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')
[dokumenty]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')
[dokumenty]class Upper(Transform): function = 'UPPER' lookup_name = 'upper'
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