Databases Reference
In-Depth Information
CHAPTER
5
IN THIS CHAPTER
.
Filtering with LINQ
.
Creating a Filter Template
.
Dynamic LINQ Queries
.
Building Search Pages with
Filter Templates
.
Filter Template Lookup Rules
S
earch functionality is essential for most database applica-
tions. Whether it is a customer browsing the product
catalog or a service representative looking up a customer
record, users need a fast and convenient mechanism for
finding the information they need. For more than a decade
now, ASP.NET developers have been using stored procedures
to implement data access code in general and search func-
tionality in particular. For each search screen, such as the
Customer search page shown in Figure 5.1, one or more
stored procedures would be created, each accepting a
number of parameters representing the search criteria and
executing an appropriate
SELECT
statement.
.
Built-in Filter Templates
Although implementing a simple page using stored proce-
dures is easy, complexity grows exponentially with the
number of additional parameters in the search criteria.
Consider the Customer search page shown in Figure 5.1.
With only 2 search parameters, City and Title, this search
page needs to support 3 different combinations of their
values—only
City
, only
Title
, and both
City
and
Title
.
This requires placing conditional logic either in the form of
IF
statements in the stored procedure body or in the form
of logical conditions in the
WHERE
clause of the
SELECT
state-
ment to handle each of the 3 combinations. With 3 search
parameters, the number of combinations jumps to 7; with 4
parameters, it is already 15; and with only 5 parameters, (a
very modest number for an advanced search page in a
typical application), the number of possible combination is
a formidable 31.
The number of possible combinations of parameter values is
important for two reasons. On one hand, it directly affects
the complexity of the database code developers have to
