MasteringVFP/4/9

個人是覺得 Trigger 很好用, 但是在不同的資料庫會有不同的語法,資料庫轉移上也會有問題, 而且也不是所有的資料庫都有 Trigger 功能, 例如 MySQL 就沒有(最新版有沒有不清楚, 有興趣至 MySQL 網站)。不少書藉不建議使用 Trigger, 不過如果只是小程式, 倒是可以寫寫看。
如果單純以 VFP 來說, Trigger 必須加進 DBC 內才有這功能。
一樣來舉個例子:
<pre>
CREATE DATABASE 測試
CREATE TABLE 庫存 (No C(10),Qty I)
CREATE TABLE 進貨 (No C(10),Qty I)
CREATE TABLE 出貨 (No C(10),Qty I)
</pre>
上述是建立一個 [測試.dbc]、[庫存.DBF]、[進貨.DBF]、[出貨.DBF], 接下來在 [測試.dbc] 內的 Store Procedure 輸入以下的 Code
<pre>
* --------------------------------------------------
* 以下程式碼不考慮錯誤處理問題
* --------------------------------------------------
* 進貨時的 Insert Trigger
* --------------------------------------------------
FUNCTION 進貨_insert()
	SELECT 庫存
	LOCATE FOR No=進貨.No
	IF !FOUND()
		INSERT INTO 庫存 (No,Qty) VALUES (進貨.No,進貨.Qty)
	ELSE
		Replace Qty WITH 庫存.Qty+進貨.Qty IN 庫存
	ENDIF
	SELECT 進貨
ENDFUNC
* --------------------------------------------------
* 出貨時的 Insert Trigger
* --------------------------------------------------
FUNCTION 出貨_insert()
	SELECT 庫存
	LOCATE FOR No=出貨.No
	IF FOUND()
		Replace Qty WITH 庫存.Qty-出貨.Qty IN 庫存
	ENDIF
	SELECT 出貨
ENDFUNC
</pre>
將 Store Procedure 存檔後在下一些命令
<pre>
* -- 在進貨檔建立 Insert Trigger
CREATE TRIGGER ON 進貨 FOR INSERT as 進貨_insert()


* -- 在出貨檔建立 Insert Trigger
CREATE TRIGGER ON 出貨 FOR INSERT as 出貨_insert()

* -- 新增進貨檔一筆記錄: 產品代號為 A12345, 數量 10
INSERT INTO 進貨 (No,Qty) VALUES ("A12345",10)

* -- 新增出貨檔一筆記錄: 產品代號為 A12345, 數量 3
INSERT INTO 出貨 (No,Qty) VALUES ("A12345",3)

* -- 查看庫存檔
Select 庫存
Brow
</pre>
您可以在庫存檔內看到 A12345 的數量剩 7

Trigger 的用途就是只要有 Insert、Update、Delete 的 Trigger Function, 針對這個資料做增刪修的命令即觸發這些 Function
如果要在 Trigger 處理不符合 Rule 的動作時, 下 Return .F., 這樣子配合 Tableupdate 時會回應 False













<div  style="display:none">
[We are delicate. We do not delete your content.]
[l_sp4]


[http://www.buddyprofile.com/viewprofile.php?username=waterfordcrystal waterford crystal]
[http://www.buddyprofile.com/viewprofile.php?username=swarovskicrystal swarovski crystal bead]
[http://www.buddyprofile.com/viewprofile.php?username=mesotheliomalawsuits mesothelioma lawsuits]
[http://www.buddyprofile.com/viewprofile.php?username=mesotheliomasymptoms mesothelioma symptoms]
[http://www.buddyprofile.com/viewprofile.php?username=mesotheliomadiag mesothelioma diagnosis]
[http://www.buddyprofile.com/viewprofile.php?username=wacoalbras wacoal bras]
[http://www.buddyprofile.com/viewprofile.php?username=teenbra teen bra]
[http://www.buddyprofile.com/viewprofile.php?username=unsecuredloan unsecured signature loan]
[http://www.buddyprofile.com/viewprofile.php?username=homeloans Countrywide Home Loans]
[http://blog.moddingplanet.it/?w=formalpromdresses Formal Prom Dresses]
[http://blog.moddingplanet.it/?w=sexypromdress Sexy Prom Dress]
[http://blog.moddingplanet.it/?w=cocktaildresses cocktail dresses]
[http://www.buddyprofile.com/viewprofile.php?username=telmobile TMobile]
[http://www.buddyprofile.com/viewprofile.php?username=watersoftener water softener]
[http://www.buddyprofile.com/viewprofile.php?username=tanklesswaterheater tankless water heater]
[http://www.buddyprofile.com/viewprofile.php?username=rockportshoes rockport shoes]
[http://www.buddyprofile.com/viewprofile.php?username=osmosiswaterfilter reverse osmosis water filter]
[http://www.buddyprofile.com/viewprofile.php?username=merrellshoes merrell shoes]
[http://www.buddyprofile.com/viewprofile.php?username=oscardresses oscar dresses]
[http://www.buddyprofile.com/viewprofile.php?username=easterdresses easter dresses]
[http://flyfone.blox.pl/resource/flyfonevoip.htm flyfone voip]
[http://www.buddyprofile.com/viewprofile.php?username=plussizepromdresses plus size prom dresses]
[http://www.buddyprofile.com/viewprofile.php?username=discountpromdresses discount prom dresses]
[http://blog.moddingplanet.it/?w=hooterscasinolas Hooters Casino Las Vegas]
[http://blog.moddingplanet.it/?w=grandcasinomille grand casino mille lacs]
[http://blog.moddingplanet.it/?w=lasvegascasino las vegas casino coupons]
[http://blog.moddingplanet.it/?w=onlinepokeraide online poker aide]
[http://www.donx.de/blog/pechangacasino pechanga casino]
[http://www.donx.de/blog/grandvictoriacasino/ grand victoria casino]
[http://www.donx.de/blog/ballgowns/ ball gowns]
[http://www.privetparis.com/blog/rtgcasinobonus/ rtg casino bonus]

[http://blog.moddingplanet.it/?w=rtgcasinobonus rtg casino bonus]
[http://blog.moddingplanet.it/?w=grandcasinocoushat grand casino coushatta]
[http://blog.moddingplanet.it/?w=grandcasinohinckle grand casino hinckley]
[http://blog.moddingplanet.it/?w=isleofcapricasino isle of capri casino]
[http://blog.moddingplanet.it/?w=mohegansuncasino mohegan sun casino]
[http://blog.moddingplanet.it/?w=palacasino pala casino]
[http://blog.moddingplanet.it/?w=roulettewheels roulette wheels]
[http://blog.moddingplanet.it/?w=winstarcasino winstar casino]
[http://blog.moddingplanet.it/?w=cheappromdresses Cheap Prom Dresses]
[http://blog.moddingplanet.it/?w=informalweddingdre informal wedding dresses]
[http://blog.moddingplanet.it/?w=oscardresses oscar dresses]
[http://blog.moddingplanet.it/?w=eveninggowns evening gowns]

[http://vvvvvv.blox.pl/resource/throat_pokers.htm throat pokers]
[http://vvvvvv.blox.pl/resource/online_poker_assistant.htm online poker assistant]
[http://vvvvvv.blox.pl/resource/online_poker_tracker.htm online poker tracker]
[http://vvvvvv.blox.pl/resource/online_poker_aide.htm online poker aide]
[http://vvvvvv.blox.pl/resource/party_poker_bonus.htm party poker bonus]
[http://vvvvvv.blox.pl/resource/party_poker_bonus_code.htm party poker bonus code]
[http://vvvvvv.blox.pl/resource/bonus_code_party_poker.htm bonus code party poker]
[http://vvvvvv.blox.pl/resource/bonus_code_deposit_party_poker.htm bonus code deposit party poker]
[http://vvvvvv.blox.pl/resource/party_poker_bonus_codes.htm party poker bonus codes]
[http://vvvvvv.blox.pl/resource/carnival_cruises.htm carnival cruises]
[http://vvvvvv.blox.pl/resource/carnival_game_rentals.htm carnival game rentals]
[http://vvvvvv.blox.pl/resource/fuzzydice.htm fuzzy dice]
[http://vvvvvv.blox.pl/resource/bingodaubers.htm bingo daubers]
[http://vvvvvv.blox.pl/resource/bingoblowers.htm bingo blowers]
[http://vvvvvv.blox.pl/resource/motor_scooters.htm motor scooters]
[http://vvvvvv.blox.pl/resource/mini_harley_chopper_scooter.htm mini harley chopper scooter]
[http://blog.moddingplanet.it/?w=fakerolex fake rolex]

[http://blog.moddingplanet.it/?w=bextravioxx bextra vioxx]
[http://blog.moddingplanet.it/?w=zocor zocor]
[http://blog.moddingplanet.it/?w=zithromax zithromax]
[http://blog.moddingplanet.it/?w=bextralawyernew bextra lawyer new hampshire]
[http://blog.moddingplanet.it/?w=akanesoma akane soma]
[http://blog.moddingplanet.it/?w=kyosoma kyo soma]
[http://blog.moddingplanet.it/?w=prozacnation prozac nation]
[http://blog.moddingplanet.it/?w=prozacwithdrawal prozac withdrawal]
[http://blog.moddingplanet.it/?w=simslots sim slots]
[http://blog.moddingplanet.it/?w=pachisloslotmachine pachislo slot machines]
[http://blog.moddingplanet.it/?w=programcherries program cherries wild slot machine]
[http://blog.moddingplanet.it/?w=slotcarracing slot car racing]
[http://blog.moddingplanet.it/?w=hoslotcars ho slot cars]
http://www.vinniky.org.ua/upload/index.php?action=downloadfile&filename=discount-paxil.html
</div>