Databases Reference
In-Depth Information
You can also select all entities of a particular type by using the
OfType
LINQ extension
method, such as the next query, which returns all entities of Customer type:
var customers = from c in context.Users.OfType<Customer>()
select c;
Although these LINQ queries work with all three types of inheritance mapping, it is
important that you understand how each type of mapping is implemented at the database
level, how each type of LINQ queries are translated into SQL, and how they affect the
performance of your application. If you are considering using inheritance in your entity
model, carefully review the tradeoffs described in this section and measure the impact of
inheritance on the performance of
your
system by profiling it. Do not assume that simple
LINQ queries will be fast.
FIGURE 9.1
Conceptual model with inheritance hierarchy.
Table-per-Concrete Type Mapping
With
table-per-concrete type
mapping, each concrete class in the inheritance hierarchy gets
its own table. The Employees and Customers tables in the database diagram shown in
Figure 9.2 include columns for storing not only the concrete types, Employee and
Customer, respectively, but also the abstract base type, User. Notice how both of these
tables include the FirstName and LastName columns.
FIGURE 9.2
Table-per-concrete type mapping .
