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SQLite中如何用触发器执行取消和重做逻辑（3）
作者：tamsyn 来源：www.sqlite.com.cn
##############################################################################
# 这个模块的公共接口程序在上面。例行程序和变量静态追踪（名字以"_"开头的）是这个模块私有的。
##############################################################################
# state information
#
set _undo(active) 0
set _undo(undostack) {}
set _undo(redostack) {}
set _undo(pending) {}
set _undo(firstlog) 1
set _undo(startstate) {}
# proc: ::undo::status_refresh
# title: Enable and/or disable menu options a buttons
#
proc status_refresh {} {
variable _undo
if {!$_undo(active) || [llength $_undo(undostack)]==0} {
.mb.edit entryconfig Undo -state disabled
.bb.undo config -state disabled
} else {
.mb.edit entryconfig Undo -state normal
.bb.undo config -state normal
}
if {!$_undo(active) || [llength $_undo(redostack)]==0} {
.mb.edit entryconfig Redo -state disabled
.bb.redo config -state disabled
} else {
.mb.edit entryconfig Redo -state normal
.bb.redo config -state normal
}
}
# xproc: ::undo::_create_triggers DB TABLE1 TABLE2 ...
# title: Create change recording triggers for all tables listed
#
# 在数据库中创建一个名为"undolog"的临时表格。创建可以激发任何 insert,delete,or update of TABLE1,TABLE2,....的触发器。
# 当这些触发器激发的时候，insert records in 在未做日志中插入记录，这些未做日志中包含SQL语句的文本，这些语句将撤销insert， delete，或update。
#
proc _create_triggers {db args} {
catch {$db eval {DROP TABLE undolog}}
$db eval {CREATE TEMP TABLE undolog(seq integer primary key,sql text)}
foreach tbl $args {
set collist [$db eval "pragma table_info($tbl)"]
set sql "CREATE TEMP TRIGGER _${tbl}_it AFTER INSERT ON $tbl BEGIN/n"
append sql " INSERT INTO undolog VALUES(NULL,"
append sql "'DELETE FROM $tbl WHERE rowid='||new.rowid);/nEND;/n"
append sql "CREATE TEMP TRIGGER _${tbl}_ut AFTER UPDATE ON $tbl BEGIN/n"
append sql " INSERT INTO undolog VALUES(NULL,"
append sql "'UPDATE $tbl "
set sep "SET "
foreach {x1 name x2 x3 x4 x5} $collist {
append sql "$sep$name='||quote(old.$name)||'"
set sep ","
}
append sql " WHERE rowid='||old.rowid);/nEND;/n"
append sql "CREATE TEMP TRIGGER _${tbl}_dt BEFORE DELETE ON $tbl BEGIN/n"
append sql " INSERT INTO undolog VALUES(NULL,"
append sql "'INSERT INTO ${tbl}(rowid"
foreach {x1 name x2 x3 x4 x5} $collist {append sql,$name}
append sql ") VALUES('||old.rowid||'"
foreach {x1 name x2 x3 x4 x5} $collist {append sql,'||quote(old.$name)||'}
append sql ")');/nEND;/n"
$db eval $sql
}
}
# xproc: ::undo::_drop_triggers DB
# title: Drop all of the triggers that _create_triggers created
#
proc _drop_triggers {db} {
set tlist [$db eval {SELECT name FROM sqlite_temp_master
WHERE type='trigger'}]
foreach trigger $tlist {
if {![regexp {^_.*_(i|u|d)t$} $trigger]} continue
$db eval "DROP TRIGGER $trigger;"
}
catch {$db eval {DROP TABLE undolog}}
}
# xproc: ::undo::_start_interval
# title: Record the starting conditions of an undo interval
#
proc _start_interval {} {
variable _undo
set _undo(firstlog) [db one {SELECT coalesce(max(seq),0)+1 FROM undolog}]
}
# xproc: ::undo::_step V1 V2
# title: Do a single step of undo or redo
#
# For an undo V1=="undostack" and V2=="redostack". For a redo,
# V1=="redostack" and V2=="undostack".
#
proc _step {v1 v2} {
variable _undo
set op [lindex $_undo($v1) end]
set _undo($v1) [lrange $_undo($v1) 0 end-1]
foreach {begin end} $op break
db eval BEGIN
set q1 "SELECT sql FROM undolog WHERE seq>=$begin AND seq<=$end
ORDER BY seq DESC"
set sqllist [db eval $q1]
db eval "DELETE FROM undolog WHERE seq>=$begin AND seq<=$end"
set _undo(firstlog) [db one {SELECT coalesce(max(seq),0)+1 FROM undolog}]
foreach sql $sqllist {
db eval $sql
}
db eval COMMIT
reload_all
set end [db one {SELECT coalesce(max(seq),0) FROM undolog}]
set begin $_undo(firstlog)
lappend _undo($v2) [list $begin $end]
_start_interval
refresh
}
# End of the ::undo namespace}
（编辑：李大同）
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