I am working on filter mechanism using expressions and can't figure out how call Any method using Expression.Call. Below is example which doesn't make sense but illustrates my problem :
var person = new List<String>(new[] { "Peter", "John", "Jim" });
var personQuery = person.AsQueryable();
var anyMethod = typeof(Queryable).GetMethods().FirstOrDefault(method => method.Name == "Any" && method.GetParameters().Count() == 2);
Expression<Func<String, bool>> expr = p => p == "Amy";
// person.Any(person => person == "Amy"
var call = Expression.Call(
anyMethod,
personQuery.Expression,
expr
);
Expression.Call throws ArgumentException:
System.ArgumentException was unhandled
HResult=-2147024809
Message=Method Boolean Any[TSource](System.Linq.IQueryable`1[TSource], System.Linq.Expressions.Expression`1[System.Func`2[TSource,System.Boolean]]) is a generic method definition.
Source=System.Core
StackTrace:
w System.Linq.Expressions.Expression.ValidateMethodInfo(MethodInfo method)
w System.Linq.Expressions.Expression.ValidateMethodAndGetParameters(Expression instance, MethodInfo method)
w System.Linq.Expressions.Expression.Call(MethodInfo method, Expression arg0, Expression arg1)
w TestConsoleApplication.Program.Main(String[] args) w d:\Users\user\Documents\Visual Studio 2012\Projects\TestConsoleApplication\TestConsoleApplication\Program.cs:wiersz 26
w System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
w System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
w Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
w System.Threading.ThreadHelper.ThreadStart_Context(Object state)
w System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
w System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
w System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
w System.Threading.ThreadHelper.ThreadStart()
InnerException:
Your anyMethod
variable will contain generic method definition. I.e Any<TSource>
you need to convert it to Any<String>
before invoking it.
You'll do it by calling anyMethod.MakeGenericMethod
providing typeof(String)
argument. So your code becomes
var person = new List<String>(new[] { "Peter", "John", "Jim" });
var personQuery = person.AsQueryable();
var anyMethod = typeof(Queryable).GetMethods().FirstOrDefault(method => method.Name == "Any" && method.GetParameters().Count() == 2);
var specificMethod = anyMethod.MakeGenericMethod(typeof(String));//<--Important
Expression<Func<String, bool>> expr = p => p == "Amy";
// person.Any(person => person == "Amy"
var call = Expression.Call(
specificMethod,
personQuery.Expression,
expr
);
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