Build Expression Equals on string
.net, c#, c#-4.0, expression
Solution
As the error message explains, there is more than one `Equals` method defined on the `string` type - `Equals(object)` and `Equals(string)`. Since you are only using the name to locate the method you want, the match is ambiguous.
One solution is to pass the `MethodInfo` for the method to `Expression.Call` e.g.
MethodInfo equalsMethod = typeof(string).GetMethod("Equals", new[] { typeof(string) });
Expression.Call(instanceExpr, equalsMethod, Expression.Constant(value.ToString().ToUpper()));
Problem
The code below works with `StartsWith` and `Contains` but when I tried `Equals` I get this exception : More than one method 'Equals' on type 'System.String' is compatible with the supplied arguments. To resume, the CreatePredicate can build 3 types of predicate but only the `Equals` does not work : - `AList.Where(x => x.MyField.StartsWith("ValueToSearch")); //OK` - `AList.Where(x => x.MyField.Contains("ValueToSearch")); //OK` - `AList.Where(x => x.MyField.Equals("ValueToSearch")); //Not OK` .. ``` public enum TypeSearch { StartsWith = 1, Contains = 2, Equals = 3 } private static Expression<Func<T, bool>> CreatePredicate<T>(string member, object value, TypeSearch type) { var p = System.Linq.Expressions.Expression.Parameter(typeof(T)); System.Linq.Expressions.Expression body = p; foreach (var subMember in member.Split('.')) { body = System.Linq.Expressions.Expression.PropertyOrField(body, subMember); } var res = System.Linq.Expressions.Expression.Lambda<Func<T, bool>>( System.Linq.Expressions.Expression.Call( System.Linq.Expressions.Expression.Call( body, "ToUpper", null), type.ToString(), null, System.Linq.Expressions.Expression.Constant(value.ToString().ToUpper()) ), p); return res; } ```