226 lines
7.9 KiB
Python
226 lines
7.9 KiB
Python
"""
|
|
Classes that represent database functions.
|
|
"""
|
|
from django.db.models import Func, Transform, Value, fields
|
|
|
|
|
|
class Cast(Func):
|
|
"""
|
|
Coerce an expression to a new field type.
|
|
"""
|
|
function = 'CAST'
|
|
template = '%(function)s(%(expressions)s AS %(db_type)s)'
|
|
|
|
mysql_types = {
|
|
fields.CharField: 'char',
|
|
fields.IntegerField: 'signed integer',
|
|
fields.FloatField: 'signed',
|
|
}
|
|
|
|
def __init__(self, expression, output_field):
|
|
super(Cast, self).__init__(expression, output_field=output_field)
|
|
|
|
def as_sql(self, compiler, connection, **extra_context):
|
|
if 'db_type' not in extra_context:
|
|
extra_context['db_type'] = self._output_field.db_type(connection)
|
|
return super(Cast, self).as_sql(compiler, connection, **extra_context)
|
|
|
|
def as_mysql(self, compiler, connection):
|
|
extra_context = {}
|
|
output_field_class = type(self._output_field)
|
|
if output_field_class in self.mysql_types:
|
|
extra_context['db_type'] = self.mysql_types[output_field_class]
|
|
return self.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')
|
|
|
|
|
|
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()]
|
|
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):
|
|
"""
|
|
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()
|
|
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(ConcatPair, self).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
|
|
|
|
|
|
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:]))
|
|
|
|
|
|
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')
|
|
|
|
|
|
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')
|
|
|
|
|
|
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', fields.IntegerField())
|
|
super(Length, self).__init__(expression, output_field=output_field, **extra)
|
|
|
|
def as_mysql(self, compiler, connection):
|
|
return super(Length, self).as_sql(compiler, connection, function='CHAR_LENGTH')
|
|
|
|
|
|
class Lower(Transform):
|
|
function = 'LOWER'
|
|
lookup_name = 'lower'
|
|
|
|
|
|
class Now(Func):
|
|
template = 'CURRENT_TIMESTAMP'
|
|
|
|
def __init__(self, output_field=None, **extra):
|
|
if output_field is None:
|
|
output_field = fields.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.
|
|
return self.as_sql(compiler, connection, template='STATEMENT_TIMESTAMP()')
|
|
|
|
|
|
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):
|
|
return super(Substr, self).as_sql(compiler, connection, function='SUBSTR')
|
|
|
|
def as_oracle(self, compiler, connection):
|
|
return super(Substr, self).as_sql(compiler, connection, function='SUBSTR')
|
|
|
|
|
|
class Upper(Transform):
|
|
function = 'UPPER'
|
|
lookup_name = 'upper'
|