Hide keyboard shortcuts

Hot-keys on this page

r m x p   toggle line displays

j k   next/prev highlighted chunk

0   (zero) top of page

1   (one) first highlighted chunk

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/>. 

21 

22from __future__ import annotations 

23 

24__all__ = ("SimpleQuery",) 

25 

26from typing import ( 

27 Any, 

28 ClassVar, 

29 List, 

30 Optional, 

31 Union, 

32 Type, 

33 TypeVar, 

34) 

35 

36import sqlalchemy 

37 

38 

39T = TypeVar("T") 

40 

41 

42class SimpleQuery: 

43 """A struct that combines SQLAlchemy objects representing SELECT, FROM, 

44 and WHERE clauses. 

45 """ 

46 

47 def __init__(self) -> None: 

48 self.columns = [] 

49 self.where = [] 

50 self._from: Optional[sqlalchemy.sql.FromClause] = None 

51 

52 class Select: 

53 """Tag class used to indicate that a field should be returned in 

54 a SELECT query. 

55 """ 

56 

57 Or: ClassVar 

58 

59 Select.Or = Union[T, Type[Select]] 

60 """A type annotation for arguments that can take the `Select` type or some 

61 other value. 

62 """ 

63 

64 def join(self, table: sqlalchemy.sql.FromClause, *, 

65 onclause: Optional[sqlalchemy.sql.ColumnElement] = None, 

66 isouter: bool = False, 

67 full: bool = False, 

68 **kwargs: Any) -> None: 

69 """Add a table or subquery join to the query, possibly adding 

70 SELECT columns or WHERE expressions at the same time. 

71 

72 Parameters 

73 ---------- 

74 table : `sqlalchemy.sql.FromClause` 

75 Table or subquery to include. 

76 onclause : `sqlalchemy.sql.ColumnElement`, optional 

77 Expression used to join the new table or subquery to those already 

78 present. Passed directly to `sqlalchemy.sql.FromClause.join`, but 

79 ignored if this is the first call to `SimpleQuery.join`. 

80 isouter : `bool`, optional 

81 If `True`, make this an LEFT OUTER JOIN. Passed directly to 

82 `sqlalchemy.sql.FromClause.join`. 

83 full : `bool`, optional 

84 If `True`, make this a FULL OUTER JOIN. Passed directly to 

85 `sqlalchemy.sql.FromClause.join`. 

86 **kwargs 

87 Additional keyword arguments correspond to columns in the joined 

88 table or subquery. Values may be: 

89 

90 - `Select` (a special tag type) to indicate that this column 

91 should be added to the SELECT clause as a query result; 

92 - `None` to do nothing (equivalent to no keyword argument); 

93 - Any other value to add an equality constraint to the WHERE 

94 clause that constrains this column to the given value. Note 

95 that this cannot be used to add ``IS NULL`` constraints, because 

96 the previous condition for `None` is checked first. 

97 """ 

98 if self._from is None: 

99 self._from = table 

100 elif onclause is not None: 

101 self._from = self._from.join(table, onclause=onclause, isouter=isouter, full=full) 

102 else: 

103 # New table is completely unrelated to all already-included 

104 # tables. We need a cross join here but SQLAlchemy does not 

105 # have a specific method for that. Using join() without 

106 # `onclause` will try to join on FK and will raise an exception 

107 # for unrelated tables, so we have to use `onclause` which is 

108 # always true. 

109 self._from = self._from.join(table, sqlalchemy.sql.literal(True)) 

110 for name, arg in kwargs.items(): 

111 if arg is self.Select: 

112 self.columns.append(table.columns[name].label(name)) 

113 elif arg is not None: 

114 self.where.append(table.columns[name] == arg) 

115 

116 def combine(self) -> sqlalchemy.sql.Select: 

117 """Combine all terms into a single query object. 

118 

119 Returns 

120 ------- 

121 sql : `sqlalchemy.sql.Select` 

122 A SQLAlchemy object representing the full query. 

123 """ 

124 result = sqlalchemy.sql.select(self.columns) 

125 if self._from is not None: 

126 result = result.select_from(self._from) 

127 if self.where: 

128 result = result.where(sqlalchemy.sql.and_(*self.where)) 

129 return result 

130 

131 @property 

132 def from_(self) -> sqlalchemy.sql.FromClause: 

133 """The FROM clause of the query (`sqlalchemy.sql.FromClause`). 

134 

135 This property cannot be set. To add tables to the FROM clause, call 

136 `join`. 

137 """ 

138 return self._from 

139 

140 def copy(self) -> SimpleQuery: 

141 """Return a copy of this object, with new lists for the `where` and 

142 `columns` attributes that can be modified without changing the 

143 original. 

144 

145 Returns 

146 ------- 

147 copy : `SimpleQuery` 

148 A copy of ``self``. 

149 """ 

150 result = SimpleQuery() 

151 result.columns = list(self.columns) 

152 result.where = list(self.where) 

153 result._from = self._from 

154 return result 

155 

156 columns: List[sqlalchemy.sql.ColumnElement] 

157 """The columns in the SELECT clause 

158 (`list` [ `sqlalchemy.sql.ColumnElement` ]). 

159 """ 

160 

161 where: List[sqlalchemy.sql.ColumnElement] 

162 """Boolean expressions that will be combined with AND to form the WHERE 

163 clause (`list` [ `sqlalchemy.sql.ColumnElement` ]). 

164 """