concept query - builder method in category .net
This is an excerpt from Manning's book Entity Framework 4 in Action.
Because Entity SQL is string-based, query-builder methods, and Entity SQL in general, make runtime construction easy. The following listing shows the code required for runtime query construction using both LINQ to Entities and query-builder methods.
, as compared to seven 
. Isn’t that great? You should now understand why we said that Entity SQL in combination with query-builder methods is more useful than LINQ to Entities in such cases. Query-builder methods are a convenient way to organize Entity SQL queries and can often simplify dynamic query creation. These methods do exactly what their name suggests: they let you build an Entity SQL query using methods instead of having to write the entire Entity SQL on your own. Query-builder methods don’t cover all aspects of querying, but, in our experience, 90% of a project’s queries can be developed using them.
Query-builder methods aren’t extension methods like the LINQ to Entities methods. They’re included in the ObjectQuery<T> class and implement the fluent technique, which allows them to be chained, because they return an ObjectQuery<T> instance. The query-builder methods are listed in table 9.1.
Table 9.1. The query-builder methods
Method
Functionality
Distinct Specifies that returned data must be unique Except Limits query results by excluding results based on the results of another object query Include Eager-loads related associations Intersect Limits query results by including only the results that exist in another object query OfType<T> Retrieves only instances of objects of the specified type OrderBy Defines the sorting properties Select Defines the properties to retrieve SelectValue<T> Defines the properties to retrieve, and returns them in the object specified Skip Sorts the data by a key, and skips the first n occurrences Top Returns only the first n occurrences Union Merges the results of two queries, removing duplicates UnionAll Merges the results of two queries Where Defines filters