namespace<\/span> ALinqExtensions<\/span><\/div>{<\/span><\/div> using<\/span> System.Linq.Expressions<\/span>;<\/span><\/div> public<\/span> static<\/span> class<\/span> SetBasedExtensions<\/span> {<\/span><\/div> <\/div>
public<\/span> static<\/span> DataServiceQuery<\/span><<\/span>T<\/span>><\/span> IsIn<\/span><<\/span>T<\/span>>(<\/span>this<\/span> DataServiceQuery<\/span><<\/span>T<\/span>><\/span> query<\/span>,<\/span> IEnumerable<\/span> Set<\/span>,<\/span> Expression<\/span><<\/span>Func<\/span><<\/span>T<\/span>,<\/span>Object<\/span>>><\/span> propertyExpression<\/span>)<\/span> {<\/span><\/div> <\/div>
//The Filter Predicate that contains the Filter criteria<\/span><\/div> Expression<\/span> filterPredicate<\/span> =<\/span> null<\/span>;<\/span><\/div> //The parameter expression containing the Entity Type<\/span><\/div> ParameterExpression<\/span> param<\/span> =<\/span> propertyExpression<\/span>.<\/span>Parameters<\/span>.<\/span>Single<\/span>();<\/span><\/div> //Get Key Property <\/span><\/div> //The Left Hand Side of the Filter Expression<\/span><\/div> Expression<\/span> left<\/span> =<\/span> propertyExpression<\/span>.<\/span>Body<\/span>;<\/span><\/div> //Build a Dynamic Linq Query for finding an entity whose ID is in the list<\/span><\/div> foreach<\/span> (<\/span>var<\/span> id<\/span> in<\/span> Set<\/span>)<\/span> {<\/span> <\/div> //Build a comparision expression which equats the Id of the ENtity with this value in the IDs list<\/span><\/div> // ex : e.Id == 1<\/span><\/div> Expression<\/span> comparison<\/span> =<\/span> Expression<\/span>.<\/span>Equal<\/span>(<\/span>left<\/span>,<\/span> Expression<\/span>.<\/span>Constant<\/span>(<\/span>id<\/span>));<\/span><\/div> //Add this to the complete Filter Expression<\/span><\/div> // e.Id == 1 or e.Id == 3<\/span><\/div> filterPredicate<\/span> =<\/span> (<\/span>filterPredicate<\/span> ==<\/span> null<\/span>)<\/span> ?<\/span> comparison<\/span> :<\/span> Expression<\/span>.<\/span>Or<\/span>(<\/span>filterPredicate<\/span>,<\/span> comparison<\/span>);<\/span><\/div> }<\/span><\/div> <\/div>
//Convert the Filter Expression into a Lambda expression of type Func<Lists,bool><\/span><\/div> // which means that this lambda expression takes an instance of type EntityType and returns a Bool<\/span><\/div> var<\/span> filterLambdaExpression<\/span> =<\/span> Expression<\/span>.<\/span>Lambda<\/span><<\/span>Func<\/span><<\/span>T<\/span>,<\/span> bool<\/span>>>(<\/span>filterPredicate<\/span>,<\/span> param<\/span>);<\/span><\/div> return<\/span> (<\/span>DataServiceQuery<\/span><<\/span>T<\/span>>)<\/span>query<\/span>.<\/span>Where<\/span><<\/span>T<\/span>>(<\/span>filterLambdaExpression<\/span>);<\/span><\/div> <\/div>
}<\/span> <\/div>}<\/span><\/div>//Sample usage <\/span><\/div> <\/div>
private<\/span> void<\/span> ContactsInCityIVisit<\/span>()<\/span> {<\/span><\/div> //Create the Northwind Client Context<\/span><\/div> northwindContext<\/span> nwContext<\/span> =<\/span> new<\/span> northwindContext<\/span>(<\/span><\/div> new<\/span> Uri<\/span>(<\/span>"http://ServiceEndPoint/Northwind.svc"<\/span>)<\/span><\/div> );<\/span><\/div> //The set in which we have to search for a match<\/span><\/div> List<\/span><<\/span>string<\/span>><\/span> citiesIWillVisit<\/span> =<\/span> new<\/span> List<\/span><<\/span>string<\/span>>()<\/span> {<\/span><\/div> "London"<\/span>,<\/span><\/div> "Berlin"<\/span>,<\/span><\/div> "Prague"<\/span><\/div> };<\/span><\/div> var<\/span> customersAround<\/span> =<\/span> nwContext<\/span>.<\/span>Customers<\/span>.<\/span>IsIn<\/span><<\/span>Customers<\/span>>(<\/span>citiesIWillVisit<\/span>,<\/span> c<\/span>=><\/span> c<\/span>.<\/span>