数据保存时,出现‘record not found or changed by another user’错误信息的解决办法

本文探讨了在使用TDataSetProvider进行数据更新时遇到的'recordnotfoundorchangedby anotheruser'错误。通过调整UpdateMode参数及正确设置主键字段,可以有效避免此问题。

'record not found or changed by  another user',这个错误是我在做项目时,遇到的问题,找了一些参考才解决。如下:
所用的控件有:TDataSetProvider,TADOQuery,TClientDataSet
1.当 DataSetProvider.UpdateMode=upWhereAll 时,update时 where 是指定全部字段,比如,你有a、b、c 3个字段,修改了c字段,在app server中修改的命令是update ... set c=新c where a=旧a and b=旧b and c=旧c
如果 旧的a、b、c之一 已经被其他人改掉了,那where就找不到合适的记录来修改了。所以报告“记录被其他人修改”,这个问题和“锁定”是无关的。

2.当 DataSetProvider.UpdateMode=upWhereKeyOnly 时,update时 where 是指定key字段,比如,
你有a、b、c 3个字段,修改了c字段,a是key field在app server中修改的命令是
update ... set c=新c where a=旧a (只比较a字段)你的程序应该设计为客户修改不到主键字段的值,这样
你的客户只能修改到其他字段的值,其他字段不会出现在where中,就不会出现你说的问题了。

(用第2种方法解决,注意如果你的表原来没有主键的,需要双击dataset,添加你的所有field,在有唯一值的field的 ProviderFlasgs 属性里面 InKey 设置为 true (该field必须是有唯一值的,能相当于主键的,也就是能唯一确定该行记录的),TADOQuery,TClientDataSet控件里的唯一值的field字都要设置InKey为true)

翻译成中文,只做翻译: 9. Conflict Resolution A conflict occurs when a Multicast DNS responder has a unique record for which it is currently authoritative, and it receives a Multicast DNS response message containing a record with the same name, rrtype and rrclass, but inconsistent rdata. What may be considered inconsistent is context sensitive, except that resource records with identical rdata are never considered inconsistent, even if they originate from different hosts. This is to permit use of proxies and other fault-tolerance mechanisms that may cause more than one responder to be capable of issuing identical answers on the network. A common example of a resource record type that is intended to be unique, not shared between hosts, is the address record that maps a host's name to its IP address. Should a host witness another host announce an address record with the same name but a different IP address, then that is considered inconsistent, and that address record is considered to be in conflict. Whenever a Multicast DNS responder receives any Multicast DNS response (solicited or otherwise) containing a conflicting resource record in any of the Resource Record Sections, the Multicast DNS responder MUST immediately reset its conflicted unique record to probing state, and go through the startup steps described above in Section 8, "Probing and Announcing on Startup". The protocol used in the Probing phase will determine a winner and a loser, and the loser MUST cease using the name, and reconfigure. It is very important that any host receiving a resource record that conflicts with one of its own MUST take action as described above. In the case of two hosts using the same host name, where one has been configured to require a unique host name and the other has not, the one that has not been configured to require a unique host name will not perceive any conflict, and will not take any action. By reverting to Probing state, the host that desires a unique host name will go through the necessary steps to ensure that a unique host name is obtained. The recommended course of action after probing and failing is as follows: 1. Programmatically change the resource record name in an attempt to find a new name that is unique. This could be done by adding some further identifying information (e.g., the model name of the hardware) if it is not already present in the name, or appending the digit "2" to the name, or incrementing a number at the end of the name if one is already present. 2. Probe again, and repeat as necessary until a unique name is found. 3. Once an available unique name has been determined, by probing without receiving any conflicting response, record this newly chosen name in persistent storage so that the device will use the same name the next time it is power-cycled. 4. Display a message to the user or operator informing them of the name change. For example: The name "Bob's Music" is in use by another music server on the network. Your music collection has been renamed to "Bob's Music (2)". If you want to change this name, use [describe appropriate menu item or preference dialog here]. The details of how the user or operator is informed of the new name depends on context. A desktop computer with a screen might put up a dialog box. A headless server in the closet may write a message to a log file, or use whatever mechanism (email, SNMP trap, etc.) it uses to inform the administrator of error conditions. On the other hand, a headless server in the closet may not inform the user at all -- if the user cares, they will notice the name has changed, and connect to the server in the usual way (e.g., via web browser) to configure a new name. 5. After one minute of probing, if the Multicast DNS responder has been unable to find any unused name, it should log an error message to inform the user or operator of this fact. This situation should never occur in normal operation. The only situations that would cause this to happen would be either a deliberate denial-of-service attack, or some kind of very obscure hardware or software bug that acts like a deliberate denial-of-service attack. These considerations apply to address records (i.e., host names) and to all resource records where uniqueness (or maintenance of some other defined constraint) is desired.
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