Question

The problem is :

There are two pages , one for editing name records and one for adding name records.
If I first open an edit page,then I open an add page , and input a name in add page
before I submit the name, I use the edit page to change the name,
(say change from varChar to integer type)
,after that, return to add page and submit the name.
Should this cause an error? How can I prevent this error?

Answer 1

In most web applications that I have used, the first valid request to be processed wins. I think you need to clarify your question, though, as it doesn’t sound like the situation you describe would be possible, or it would not be a problem.

It sounds like NAME is a field in a record, not an entire record on its own. It doesn’t seem like you could change the NAME field and add it at the same time. Let’s imagine you have a record type PERSON that is backed by a table in your database. Each PERSON record has a NAME field that is currently of varChar type. It sounds like you are using a web interface to edit the structure of this table.

If the table already has a field NAME, the add page submission will report an error because a field called NAME already exists. The edit page would succeed, assuming it is possible to convert the NAME field to the integer type: either there are no records, or the value of NAME in every record can be converted to an integer.

Another interpretation of your question is that you are changing the NAME field to be something else entirely in the edit screen, perhaps from NAME varChar to AGE integer. You also happen to use the add page to add a new NAME char(10), for example. This would be allowed as long as the edit page submission is processed before the add page submission.