QueryInterceptor.Core 1.0.11

QueryInterceptor.Core

The problem

Normally when you're trying to modify expression trees you need to write an expression visitor. When trying to plug your expression visitor into an IQuerable's expression tree, you need to write a linq provider (yikes).

Implementation based on http://stackoverflow.com/questions/1839901/how-to-wrap-entity-framework-to-intercept-the-linq-expression-just-before-executi

The solution

QueryInterceptor introduces one extension method on IQueryable<T> (InterceptWith) that lets you plug in arbitrary expression visitors.

namespace QueryInterceptor
{
 public static class QueryableExtensions
 {
 public static IQueryable<T> InterceptWith<T>(this IQueryable<T> source, params ExpressionVisitor[] visitors);
 }
}

Basic Example

The example below uses an expression visitor that changes == to != anywhere in the expression tree.

public class EqualsToNotEqualsVisitor : ExpressionVisitor 
{
 protected override Expression VisitBinary(BinaryExpression node) 
 {
 if (node.NodeType == ExpressionType.Equal) 
 {
 // Change == to !=
 return Expression.NotEqual(node.Left, node.Right);
 }

 return base.VisitBinary(node);
 }
}

class Program 
{
 static void Main(string[] args) 
 {
 var query = from n in Enumerable.Range(0, 10).AsQueryable()
 where n % 2 == 0
 select n;

 // Print even numbers
 foreach (var item in query)
 {
 Console.WriteLine(item);
 }

 Console.WriteLine();

 // Print odd numbers
 var visitor = new EqualsToNotEqualsVisitor();
 foreach (var item in query.InterceptWith(visitor))
 {
 Console.WriteLine(item);
 }
 }
}

Sponsors

Entity Framework Extensions and Dapper Plus are major sponsors and proud to contribute to the development of QueryInterceptor.Core.

👁 Entity Framework Extensions

👁 Dapper Plus