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type as its base type Entities with a base type inherit all the properties from that base An entity cannot specify more than one base type, but you are allowed to derive from an entity that derives from another entity (ie, you can have an inheritance chain) And the corresponding generated entity classes that you use from C# will represent these inheritance relationships with normal class inheritance You will need to define mappings for your base entity type in the usual way All the derived types will inherit these mappings The question is: how do we map features unique to individual derived types The first mapping approach involves mapping all entity types sharing a particular base entity type to a single table in the database.

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Because we installed the Spark Visual Studio integration, we get IntelliSense in our views, as demonstrated in figure 105 To complete the alternating row styles, we increment the count using the <set /> element This element lets us assign values to variables we created earlier in our view In addition to the each attribute and <set /> element, Spark provides complex expressions for conditional operators (if .. else), macros, and more With our Spark view complete, our view renders as expected in the browser, as shown in figure 106 Because of the ASPNET MVC architecture, we can swap out view engines without needing to change our controllers or actions As we saw in this section with the Spark view engine, many view engines provide a cleaner way to create views in MVC applications.

The entity type the EF chooses to represent a particular row is chosen based on a discriminator column in the mapping you simply provide a list that says, for example, if the discriminator column contains 1, the entity type is Employee, and if it s 2, the type is Manager, while if it s 3, the type is Director, and so on These derived types will presumably have additional properties distinguishing them from one another, and these would map to nullable columns in the table They will need to be nullable, because these columns will have values only when you re using the derived types that support them non-nullable database columns need to be mapped to properties in the base entity type if you re using this mapping style The second mapping approach uses a separate table for each derived type.

Derived types still inherit the base mappings, so in this scenario, derived entity types will be involved with two or more tables: the table unique to the derived type, along with any tables used by the base type This approach requires all the tables involved to use the same primary key None of these mapping features would be much use without some way to retrieve data from the database, so we ll now look at how to execute queries in the Entity Framework..

We ve seen some simple LINQ-based examples for retrieving data from the database with the Entity Framework. Under the covers, the EF turns a LINQ query into a SQL query that the database understands. In fact, there are two ways of getting the EF to query the database for data: LINQ and something called Entity SQL. We ve seen some simple LINQ to Entities examples already, but we ll now look at it in more detail.

The Spark view engine gives us a terser, more readable markup, blending code and HTML seamlessly Because Spark supports compiling views and IntelliSense, we don t need to give up all the nice integration that Web Forms offers..

The LINQ provider for the Entity Framework, LINQ to Entities, supports all of the standard LINQ operators we saw in 8, but it works a little differently. The idea of deferred execution is still present, and it s even more important. The point at which you cause the LINQ query to execute the instant at which your code first starts trying to use the results is the point at which the EF will need to send a request to the

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database. So looking at the code from Example 14-3, the statement shown in Example 14-9 does not get anything from the database.

Summary

var orders = from order in dbContext.SalesOrderHeaders where order.OrderDate == orderDate select order;