django/db/models/functions/comparison.py
"""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 import TextField
from django.db.models.fields.json import JSONField
from django.utils.regex_helper import _lazy_re_compile
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, '$')"
return self.as_sql(compiler, connection, template=template, **extra_context)
def as_postgresql(self, compiler, connection, **extra_context):
# CAST would be valid too, but the :: shortcut syntax is more readable.
# 'expressions' is wrapped in parentheses in case it's a complex
# expression.
return self.as_sql(
compiler,
connection,
template="(%(expressions)s)::%(db_type)s",
**extra_context,
)
def as_oracle(self, compiler, connection, **extra_context):
if self.output_field.get_internal_type() == "JSONField":
# Oracle doesn't support explicit cast to JSON.
template = "JSON_QUERY(%(expressions)s, '$')"
return super().as_sql(
compiler, connection, template=template, **extra_context
)
return self.as_sql(compiler, connection, **extra_context)
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)
@property
def empty_result_set_value(self):
for expression in self.get_source_expressions():
result = expression.empty_result_set_value
if result is NotImplemented or result is not None:
return result
return None
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)
class Collate(Func):
function = "COLLATE"
template = "%(expressions)s %(function)s %(collation)s"
allowed_default = False
# 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)
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)
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_native(self, compiler, connection, *, returning, **extra_context):
class ArgJoiner:
def join(self, args):
pairs = zip(args[::2], args[1::2], strict=True)
return ", ".join([" VALUE ".join(pair) for pair in pairs])
return self.as_sql(
compiler,
connection,
arg_joiner=ArgJoiner(),
template=f"%(function)s(%(expressions)s RETURNING {returning})",
**extra_context,
)
def as_postgresql(self, compiler, connection, **extra_context):
if not connection.features.is_postgresql_16:
copy = self.copy()
copy.set_source_expressions(
[
Cast(expression, TextField()) if index % 2 == 0 else expression
for index, expression in enumerate(copy.get_source_expressions())
]
)
return super(JSONObject, copy).as_sql(
compiler,
connection,
function="JSONB_BUILD_OBJECT",
**extra_context,
)
return self.as_native(compiler, connection, returning="JSONB", **extra_context)
def as_oracle(self, compiler, connection, **extra_context):
return self.as_native(compiler, connection, returning="CLOB", **extra_context)
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)
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)