Interfaces Dynamic Filter Sorting Sorting SQL. Dynamic LINQ. Radu Nicolescu Department of Computer Science University of Auckland.

Transcription

1 Dynamic LINQ Radu Nicolescu Department of Computer Science University of Auckland 25 August / 20

2 1 IEnumerable and IQueryable 2 Dynamic LINQ 3 Dynamic filter Where 4 Dynamic sorting OrderBy 5 Dynamic sorting OrderBy on SQL 2 / 20

3 Interfaces Interface IEnumerable<T>: in-memory sequences usual implementation class Enumerable lambda expressions compiled to in-memory functions Subinterface IQueryable<T>: specialised versions other targets possible lambda expressions compiled to expression trees additional properties Expression : expression tree Provider : specialised expression tree translator, e.g. to SQL Conversions via extension methods: AsQueryable() : IEnumerable<T> IQueryable<T> AsEnumerable() : IQueryable<T> IEnumerable<T> 4 / 20

4 Dynamic LINQ Dynamic LINQ consists of several extension methods for the IQueryable interface, which allow a flexible and crisp style, where the lambdas or even the LINQ methods are determined at runtime only In a nutshell, instead of lambdas, you can write string expressions, which are dynamically parsed and translated into corresponding expression trees Implementation in file Dynamic.cs, class DynamicQueryable you can include the source into your project (VS, cmdline), or compile the source as library (DLL), which you further include in a project (VS, cmdline) or snippet (LINQPad) 6 / 20

5 Dynamic LINQ Dynamic LINQ is NOT part of the standard LINQ, but is based on third party samples and projects (in fact, we use a very early version) Dynamic LINQ dynamically composes queries using strings... Strings which come from outside should be carefully screened, otherwise there may be an injection risk If interested, you can read more about this and alternate libraries see next slide 7 / 20

6 Dynamic LINQ discussions and alternate approaches Is Injection Possible through Dynamic LINQ? is-injection-possible-through-dynamic-linq Security Issue: introduces an additional attack surface to code injection #62 https: //github.com/kahanu/system.linq.dynamic/issues/62 Building LINQ Queries at Runtime in C# Calling functions in LINQ queries What is LINQKit? 8 / 20

7 Dynamic LINQ Dynamic.cs bird s eye view Extension methods Where and OrderBy 1 namespace System. Linq. Dynamic { 2 p u b l i c s t a t i c c l a s s DynamicQueryable { 3 p u b l i c s t a t i c I Q u e r y a b l e <T> Where<T> ( 4 t h i s I Q u e r y a b l e <T> source, 5 s t r i n g p r e d i c a t e, params object [ ] v a l u e s ) 6 7 p u b l i c s t a t i c I Q u e r y a b l e <T> OrderBy<T> ( 8 t h i s I Q u e r y a b l e <T> source, 9 s t r i n g o r d e r i n g, params object [ ] v a l u e s ) / 20

8 Dynamic filter Where Enumerable Where vs equivalent Dynamic Queryable Where 1 s t r i n g [ ] v = { the, q u i c k, brown, f o x } ; 2 3 var w = v. Where ( x => x. Length == 3 ) ; 4 5 var w2 = v. AsQueryable ( ). Where ( Length == 3 ) ; 6 7 var w3 = v. AsQueryable ( ). Where ( Length 3 ) ; AsQueryable() casting required, to match the signature in DynamicQueryable w3 uses a parametrised query, which is safer if input parameters come from outside 11 / 20

9 Dynamic filter Where Enumerable Where vs equivalent Dynamic Queryable Where 1 var m y l i s t = new L i s t <MyCustomer> { 2 new MyCustomer { 3 CustomerID= r n i c, Name= Radu, Age=52}, } ; 6 7 var l 1 = m y l i s t. Where ( c => c. Age > 4 0 ) ; 8 9 var l 2 = m y l i s t. AsQueryable ( ). Where ( Age > 40 ) ; var l 3 = m y l i s t. AsQueryable ( ). Where ( Age 4 0 ) ; AsQueryable() casting required, to match the signature in DynamicQueryable l3 uses a parametrised query, which is safer / 20

10 Dynamic sorting OrderBy ASC Enumerable OrderBy vs equivalent Dynamic Queryable OrderBy 1 MyOrder [ ] MyOrders = new [ ] { 2 new MyOrder { 3 OrderID= 1010, CustomerID= r n i c,..., }, } 6 7 var a1 = MyOrders. OrderBy ( o => o. P r i c e ) 8. ThenBy ( o => o. OrderID ) ; 9 10 var a2 = MyOrders. AsQueryable ( ) 11. OrderBy ( P r i c e, OrderID ) ; Sorting on multiple criteria 14 / 20

11 Dynamic sorting OrderBy DESC Enumerable OrderBy vs equivalent Dynamic Queryable OrderBy 1 MyOrder [ ] MyOrders = new [ ] { 2 new MyOrder { 3 OrderID= 1010, CustomerID= r n i c,..., }, } 6 7 var d1 = MyOrders. OrderByDescending ( o => o. P r i c e ) 8. ThenByDescending ( o => o. OrderID ) ; 9 10 var d2 = MyOrders. AsQueryable ( ) 11. OrderBy ( P r i c e DESC, OrderID DESC ) Sorting on multiple criteria 15 / 20

12 Dynamic sorting OrderBy ASC on SQL SQL: Queryable OrderBy vs equivalent Dynamic Queryable OrderBy 1 // MyOrders refers to the population of table MyOrders 2 3 var a1 = MyOrders. OrderBy ( o => o. P r i c e ) 4. ThenBy ( o => o. OrderID ) ; 5 6 var a2 = MyOrders //. AsQueryable ( ) 7. OrderBy ( P r i c e, OrderID ) ; Sorting on multiple criteria In this case, MyOrders is already IQueryable, so no cast needed 17 / 20

13 Dynamic sorting OrderBy ASC generated SQL OrderBy( Price, OrderID ) generated SQL 1 SELECT 2 FROM [ MyOrders ] AS [ t0 ] 3 ORDER BY [ t0 ]. [ P r i c e ], [ t0 ]. [ OrderID ] Same generated SQL in both cases 18 / 20

14 Dynamic sorting OrderBy DESC on SQL SQL: Queryable OrderBy vs equivalent Dynamic Queryable OrderBy 1 // MyOrders refers to the population of table MyOrders 2 3 var d1 = MyOrders. OrderByDescending ( o => o. P r i c e ) 4. ThenByDescending ( o => o. OrderID ) ; 5 6 var d2 = MyOrders //. AsQueryable ( ) 7. OrderBy ( P r i c e DESC, OrderID DESC ) Sorting on multiple criteria In this case, MyOrders is already IQueryable, so no cast needed 19 / 20

15 Dynamic sorting OrderBy DESC generated SQL OrderBy( Price DESC, OrderID DESC ) generated SQL 1 SELECT 2 FROM [ MyOrders ] AS [ t0 ] 3 ORDER BY [ t0 ]. [ P r i c e ] DESC, [ t0 ]. [ OrderID ] DESC Same generated SQL in both cases 20 / 20