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 

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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__ = ("Select", "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 Select: 

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

44 a SELECT query. 

45 """ 

46 

47 Or: ClassVar 

48 

49 

50Select.Or = Union[T, Type[Select]] 

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

52other value. 

53""" 

54 

55 

56class SimpleQuery: 

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

58 and WHERE clauses. 

59 """ 

60 

61 def __init__(self) -> None: 

62 self.columns = [] 

63 self.where = [] 

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

65 

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

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

68 isouter: bool = False, 

69 full: bool = False, 

70 **kwargs: Any) -> None: 

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

72 SELECT columns or WHERE expressions at the same time. 

73 

74 Parameters 

75 ---------- 

76 table : `sqlalchemy.sql.FromClause` 

77 Table or subquery to include. 

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

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

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

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

82 isouter : `bool`, optional 

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

84 `sqlalchemy.sql.FromClause.join`. 

85 full : `bool`, optional 

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

87 `sqlalchemy.sql.FromClause.join`. 

88 **kwargs 

89 Additional keyword arguments correspond to columns in the joined 

90 table or subquery. Values may be: 

91 

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

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

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

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

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

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

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

99 """ 

100 if self._from is None: 

101 self._from = table 

102 else: 

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

104 for name, arg in kwargs.items(): 

105 if arg is Select: 

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

107 elif arg is not None: 

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

109 

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

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

112 

113 Returns 

114 ------- 

115 sql : `sqlalchemy.sql.Select` 

116 A SQLAlchemy object representing the full query. 

117 """ 

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

119 if self._from is not None: 

120 result = result.select_from(self._from) 

121 if self.where: 

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

123 return result 

124 

125 @property 

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

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

128 

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

130 `join`. 

131 """ 

132 return self._from 

133 

134 columns: List[sqlalchemy.sql.ColumnElement] 

135 """The columns in the SELECT clause 

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

137 """ 

138 

139 where: List[sqlalchemy.sql.ColumnElement] 

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

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

142 """