Coverage for python/lsst/daf/butler/core/simpleQuery.py : 32%

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1# This file is part of daf_butler.
2#
3# Developed for the LSST Data Management System.
4# This product includes software developed by the LSST Project
5# (http://www.lsst.org).
6# See the COPYRIGHT file at the top-level directory of this distribution
7# for details of code ownership.
8#
9# This program is free software: you can redistribute it and/or modify
10# it under the terms of the GNU General Public License as published by
11# the Free Software Foundation, either version 3 of the License, or
12# (at your option) any later version.
13#
14# This program is distributed in the hope that it will be useful,
15# but WITHOUT ANY WARRANTY; without even the implied warranty of
16# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17# GNU General Public License for more details.
18#
19# You should have received a copy of the GNU General Public License
20# along with this program. If not, see <http://www.gnu.org/licenses/>.
22from __future__ import annotations
24__all__ = ("SimpleQuery",)
26from typing import (
27 Any,
28 ClassVar,
29 List,
30 Optional,
31 Union,
32 Type,
33 TypeVar,
34)
36import sqlalchemy
39T = TypeVar("T")
42class SimpleQuery:
43 """A struct that combines SQLAlchemy objects.
45 Represents SELECT, FROM, and WHERE clauses.
46 """
48 def __init__(self) -> None:
49 self.columns = []
50 self.where = []
51 self._from: Optional[sqlalchemy.sql.FromClause] = None
53 class Select:
54 """Tag class for SELECT queries.
56 Used to indicate that a field should be returned in
57 a SELECT query.
58 """
60 Or: ClassVar[Any]
62 Select.Or = Union[T, Type[Select]]
63 """A type annotation for arguments that can take the `Select` type or some
64 other value.
65 """
67 def join(self, table: sqlalchemy.sql.FromClause, *,
68 onclause: Optional[sqlalchemy.sql.ColumnElement] = None,
69 isouter: bool = False,
70 full: bool = False,
71 **kwargs: Any) -> None:
72 """Add a table or subquery join to the query.
74 Possibly also adding SELECT columns or WHERE expressions at the same
75 time.
77 Parameters
78 ----------
79 table : `sqlalchemy.sql.FromClause`
80 Table or subquery to include.
81 onclause : `sqlalchemy.sql.ColumnElement`, optional
82 Expression used to join the new table or subquery to those already
83 present. Passed directly to `sqlalchemy.sql.FromClause.join`, but
84 ignored if this is the first call to `SimpleQuery.join`.
85 isouter : `bool`, optional
86 If `True`, make this an LEFT OUTER JOIN. Passed directly to
87 `sqlalchemy.sql.FromClause.join`.
88 full : `bool`, optional
89 If `True`, make this a FULL OUTER JOIN. Passed directly to
90 `sqlalchemy.sql.FromClause.join`.
91 **kwargs
92 Additional keyword arguments correspond to columns in the joined
93 table or subquery. Values may be:
95 - `Select` (a special tag type) to indicate that this column
96 should be added to the SELECT clause as a query result;
97 - `None` to do nothing (equivalent to no keyword argument);
98 - Any other value to add an equality constraint to the WHERE
99 clause that constrains this column to the given value. Note
100 that this cannot be used to add ``IS NULL`` constraints, because
101 the previous condition for `None` is checked first.
102 """
103 if self._from is None:
104 self._from = table
105 elif onclause is not None:
106 self._from = self._from.join(table, onclause=onclause, isouter=isouter, full=full)
107 else:
108 # New table is completely unrelated to all already-included
109 # tables. We need a cross join here but SQLAlchemy does not
110 # have a specific method for that. Using join() without
111 # `onclause` will try to join on FK and will raise an exception
112 # for unrelated tables, so we have to use `onclause` which is
113 # always true.
114 self._from = self._from.join(table, sqlalchemy.sql.literal(True))
115 for name, arg in kwargs.items():
116 if arg is self.Select:
117 self.columns.append(table.columns[name].label(name))
118 elif arg is not None:
119 self.where.append(table.columns[name] == arg)
121 def combine(self) -> sqlalchemy.sql.Select:
122 """Combine all terms into a single query object.
124 Returns
125 -------
126 sql : `sqlalchemy.sql.Select`
127 A SQLAlchemy object representing the full query.
128 """
129 result = sqlalchemy.sql.select(*self.columns)
130 if self._from is not None:
131 result = result.select_from(self._from)
132 if self.where:
133 result = result.where(sqlalchemy.sql.and_(*self.where))
134 return result
136 @property
137 def from_(self) -> sqlalchemy.sql.FromClause:
138 """Return the FROM clause of the query (`sqlalchemy.sql.FromClause`).
140 This property cannot be set. To add tables to the FROM clause, call
141 `join`.
142 """
143 return self._from
145 def copy(self) -> SimpleQuery:
146 """Return a copy of this object.
148 Returns the copy with new lists for the `where` and
149 `columns` attributes that can be modified without changing the
150 original.
152 Returns
153 -------
154 copy : `SimpleQuery`
155 A copy of ``self``.
156 """
157 result = SimpleQuery()
158 result.columns = list(self.columns)
159 result.where = list(self.where)
160 result._from = self._from
161 return result
163 columns: List[sqlalchemy.sql.ColumnElement]
164 """The columns in the SELECT clause
165 (`list` [ `sqlalchemy.sql.ColumnElement` ]).
166 """
168 where: List[sqlalchemy.sql.ColumnElement]
169 """Boolean expressions that will be combined with AND to form the WHERE
170 clause (`list` [ `sqlalchemy.sql.ColumnElement` ]).
171 """