It is sometimes useful to make inputs to an SQL statement
optinal. Doing so can be difficult, because not only must the
test be inserted conditionally, but SQL boolean operators may or
may not need to be inserted depending on whether other, possibly
optional, comparisons have been done. The sqlgroup
tag
automates the conditional insertion of boolean operators.
The sqlgroup
tag is a block tag. It can
have any number of and
and or
continuation tags.
The sqlgroup
tag has an optional attribure, required
to
specify groups that must include at least one test. This is
useful when you want to make sure that a query is qualified, but
want to be very flexible about how it is qualified.
Suppose we want to find people with a given first or nick name,
city or minimum and maximum age. Suppose we want all inputs to be
optional, but want to require some input. We can
use DTML source like the following:
<dtml-sqlgroup required>
<dtml-sqlgroup>
<dtml-sqltest name column=nick_name type=nb multiple optional>
<dtml-or>
<dtml-sqltest name column=first_name type=nb multiple optional>
</dtml-sqlgroup>
<dtml-and>
<dtml-sqltest home_town type=nb optional>
<dtml-and>
<dtml-if minimum_age>
age >= <dtml-sqlvar minimum_age type=int>
</dtml-if>
<dtml-and>
<dtml-if maximum_age>
age <= <dtml-sqlvar maximum_age type=int>
</dtml-if>
</dtml-sqlgroup>
This example illustrates how groups can be nested to control
boolean evaluation order. It also illustrates that the grouping
facility can also be used with other DTML tags like if
tags.
The sqlgroup
tag checks to see if text to be inserted contains
other than whitespace characters. If it does, then it is inserted
with the appropriate boolean operator, as indicated by use of an
and
or or
tag, otherwise, no text is inserted.