Source code for django.db.models.functions.comparison
"""Database functions that do comparisons or type conversions."""
from django.db import NotSupportedError
from django.db.models.expressions import Func, Value
from django.db.models.fields.json import JSONField
from django.utils.regex_helper import _lazy_re_compile
[docs]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_sqlite(self, compiler, connection, **extra_context):
db_type = self.output_field.db_type(connection)
if db_type in {'datetime', 'time'}:
# Use strftime as datetime/time don't keep fractional seconds.
template = 'strftime(%%s, %(expressions)s)'
sql, params = super().as_sql(compiler, connection, template=template, **extra_context)
format_string = '%H:%M:%f' if db_type == 'time' else '%Y-%m-%d %H:%M:%f'
params.insert(0, format_string)
return sql, params
elif db_type == 'date':
template = 'date(%(expressions)s)'
return super().as_sql(compiler, connection, template=template, **extra_context)
return self.as_sql(compiler, connection, **extra_context)
def as_mysql(self, compiler, connection, **extra_context):
template = None
output_type = self.output_field.get_internal_type()
# MySQL doesn't support explicit cast to float.
if output_type == 'FloatField':
template = '(%(expressions)s + 0.0)'
# MariaDB doesn't support explicit cast to JSON.
elif output_type == 'JSONField' and connection.mysql_is_mariadb:
template = "JSON_EXTRACT(%(expressions)s, '$')"
return self.as_sql(compiler, connection, template=template, **extra_context)
def as_oracle(self, compiler, connection, **extra_context):
if self.output_field.get_internal_type() == 'JSONField':
# Oracle doesn't support explicit cast to JSON.
template = "JSON_QUERY(%(expressions)s, '$')"
return super().as_sql(compiler, connection, template=template, **extra_context)
return self.as_sql(compiler, connection, **extra_context)
[docs]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, **extra_context):
# Oracle prohibits mixing TextField (NCLOB) and CharField (NVARCHAR2),
# so convert all fields to NCLOB when that type is expected.
if self.output_field.get_internal_type() == 'TextField':
clone = self.copy()
clone.set_source_expressions([
Func(expression, function='TO_NCLOB') for expression in self.get_source_expressions()
])
return super(Coalesce, clone).as_sql(compiler, connection, **extra_context)
return self.as_sql(compiler, connection, **extra_context)
[docs]class Collate(Func):
function = 'COLLATE'
template = '%(expressions)s %(function)s %(collation)s'
# Inspired from https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
collation_re = _lazy_re_compile(r'^[\w\-]+$')
def __init__(self, expression, collation):
if not (collation and self.collation_re.match(collation)):
raise ValueError('Invalid collation name: %r.' % collation)
self.collation = collation
super().__init__(expression)
def as_sql(self, compiler, connection, **extra_context):
extra_context.setdefault('collation', connection.ops.quote_name(self.collation))
return super().as_sql(compiler, connection, **extra_context)
[docs]class Greatest(Func):
"""
Return the maximum expression.
If any expression is null the return value is database-specific:
On PostgreSQL, 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, **extra_context):
"""Use the MAX function on SQLite."""
return super().as_sqlite(compiler, connection, function='MAX', **extra_context)
[docs]class JSONObject(Func):
function = 'JSON_OBJECT'
output_field = JSONField()
def __init__(self, **fields):
expressions = []
for key, value in fields.items():
expressions.extend((Value(key), value))
super().__init__(*expressions)
def as_sql(self, compiler, connection, **extra_context):
if not connection.features.has_json_object_function:
raise NotSupportedError(
'JSONObject() is not supported on this database backend.'
)
return super().as_sql(compiler, connection, **extra_context)
def as_postgresql(self, compiler, connection, **extra_context):
return self.as_sql(
compiler,
connection,
function='JSONB_BUILD_OBJECT',
**extra_context,
)
def as_oracle(self, compiler, connection, **extra_context):
class ArgJoiner:
def join(self, args):
args = [' VALUE '.join(arg) for arg in zip(args[::2], args[1::2])]
return ', '.join(args)
return self.as_sql(
compiler,
connection,
arg_joiner=ArgJoiner(),
template='%(function)s(%(expressions)s RETURNING CLOB)',
**extra_context,
)
[docs]class Least(Func):
"""
Return the minimum expression.
If any expression is null the return value is database-specific:
On PostgreSQL, 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, **extra_context):
"""Use the MIN function on SQLite."""
return super().as_sqlite(compiler, connection, function='MIN', **extra_context)
[docs]class NullIf(Func):
function = 'NULLIF'
arity = 2
def as_oracle(self, compiler, connection, **extra_context):
expression1 = self.get_source_expressions()[0]
if isinstance(expression1, Value) and expression1.value is None:
raise ValueError('Oracle does not allow Value(None) for expression1.')
return super().as_sql(compiler, connection, **extra_context)
