From fd4367cf373325a255f38eb9c5288133f6543432 Mon Sep 17 00:00:00 2001
From: Daniel Macko <daniel.s.macko@gmail.com>
Date: Thu, 24 May 2018 14:16:10 +1000
Subject: [PATCH] Ensure that dynamic LINQ expressions for filters match with
 those generated by Queryable.Where (#22)

---
 Sieve/Services/SieveProcessor.cs | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/Sieve/Services/SieveProcessor.cs b/Sieve/Services/SieveProcessor.cs
index 7930b2d..5402602 100644
--- a/Sieve/Services/SieveProcessor.cs
+++ b/Sieve/Services/SieveProcessor.cs
@@ -127,10 +127,12 @@ namespace Sieve.Services
                     var converter = TypeDescriptor.GetConverter(property.PropertyType);
                     var parameter = Expression.Parameter(typeof(TEntity), "e");
 
-                    dynamic filterValue = Expression.Constant(
-                        converter.CanConvertFrom(typeof(string)) ?
-                        converter.ConvertFrom(filterTerm.Value) :
-                        Convert.ChangeType(filterTerm.Value, property.PropertyType));
+                    
+                    dynamic constantVal = converter.CanConvertFrom(typeof(string))
+                                              ? converter.ConvertFrom(filterTerm.Value)
+                                              : Convert.ChangeType(filterTerm.Value, property.PropertyType);
+
+                    Expression filterValue = GetClosureOverConstant(constantVal);
 
                     dynamic propertyValue = Expression.PropertyOrField(parameter, property.Name);
 
@@ -201,6 +203,14 @@ namespace Sieve.Services
             return result;
         }
 
+        //Workaround to ensure that the filter value gets passed as a parameter in generated SQL from EF Core
+        //See https://github.com/aspnet/EntityFrameworkCore/issues/3361
+        private Expression GetClosureOverConstant<T>(T constant)
+        {
+            Expression<Func<T>> closure = () => constant;
+            return closure.Body;
+        }
+
         private IQueryable<TEntity> ApplySorting<TEntity>(
             ISieveModel<IFilterTerm, ISortTerm> model, 
             IQueryable<TEntity> result,