These were all examples from my project, in which I use OJB only for retrieval.
But the table aliases are not needed even if you are writing back to the database. This would still be possible if you specify a specific column name.
If you got rid of the aliases, you could achieve the functionality that I described, but writing to the database would require a word of caution (basically that the field-descriptor needs a specific column name).
Gelhar, Wallace Joseph wrote:
And if you don't specify these as readonly and you try to save the
object, the whole thing bombs. If you need this functionality, why not
create a database view to load the object model from?
-----Original Message-----
From: Bobby Lawrence [mailto:[EMAIL PROTECTED] Sent: Monday, January 24, 2005 8:32 AM
To: OJB Users List
Subject: Re: remove table alias in generated SQL?
Not having an alias would allow you to use functions and string literals. You could specify a string literal in the field-descriptor like this:
<field-descriptor name="myField" column="' 'a string literal' "> This would give you the same value for every class instance, which might not seem that useful at first, but this is exactly what I needed in my project for a brief time. At the time, I was expecting values from the database where the field did not exist yet and I needed something to test.
You could also specify functions in the field-descriptor like this: <field-descriptor name="wholeName" column="CONCAT(CONCAT(firstname, ' ', lastname) AS wholename"> If using an Oracle database, this would concatenate the first and last names to give you a whole name.
Another example on concatenation w/ Oracle without using the function: <field-descriptor name="wholeName" column="firstname || ' ' || lastname AS wholename">
All of these should be possible if OJB didn't use table aliases in its generated SQL statements.
What IS the benefit of using an alias?
Jakob Braeuchi wrote:
hi bobby,
i still do not get the benefit of not using an alias. could you please
post a sample ?
jakob
Bobby Lawrence schrieb:
Well - it seems that the alias is not needed.
If the class only goes to one table for its data, why does the table need an alias?
If an alias was not used, you could specify string literals for a column name.
Jakob Braeuchi wrote:
hi,
ojb should always use the alias in front of the column name. if it does not, it could probably not translate the attribute name into a column name.
btw: what exactly is the problem with the alias ??
jakob
Vesely, Max [IT] schrieb:
Bobby,
I was able to do it by listing field names in a ReportQuery object.
It also won't append table alias in front of the column name in this case.
Max.
-----Original Message-----
From: Bobby Lawrence [mailto:[EMAIL PROTECTED] Sent: Thursday, January 20, 2005 5:38 PM
To: ojb-user@db.apache.org
Subject: remove table alias in generated SQL?
Is there a way to tell OJB to not use the table alias in front of the column names when it generates SQL?
Currently, when you specifiy that a class comes from <tableA> and a
field of that class comes from <fieldA>, OJB executes the following SQL: SELECT A0.<fieldA> FROM <tableA> A0
If you can't map one class to multiple tables, I don't see why this
is necessary. Is there any way around this?
Instead of mapping a field to a specific column, I want to map it to a string literal so that it always has the same value for the class.
Ex. <field-descriptor column= 'some literal' AS myColumn">
-- Bobby
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