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)
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