Expression<Func<Client, bool>> expression = x => true;
                foreach (var item in searchParams)
                {
                    var operatorType = ExpressionType.Equal;
                    string propertyName = null;
                    object value = null;
                    string keyValue = item.Value;

                    if (item.Key == Constants.SearchParameterNames.Id)
                    {
                        int val = 0;
                        if (int.TryParse(keyValue, out val))
                            value = val;
                        propertyName = "ClientID";
                    }
                    else if (item.Key == Constants.SearchParameterNames.Lastupdate)
                    {
                        DateTime dateTime;
                        if (DateTime.TryParse(keyValue, out dateTime))
                            value = dateTime;
                        propertyName = "LastChange";
                    }

                    if (!string.IsNullOrWhiteSpace(propertyName) && value != null)
                    {

                            var exp = GetBinaryOperation<Client>(propertyName, operatorType, value);
                            var exp1 = Expression.And(expression.Body, exp);
                            expression = Expression.Lambda<Func<Client, bool>>(exp1, expression.Parameters);
                    }

                }
                var client = _clientRepository.FindBy(expression).ToList();

public BinaryExpression GetBinaryOperation<T>(string propertyName, ExpressionType type, object value)
    {

        var parameterExpression = Expression.Parameter(typeof(T), "x");
        var memberExpression = Expression.Property(parameterExpression, propertyName);
        var propertyType = GetMemberType(memberExpression);
        var rhs = Expression.Constant(value);
        var binaryExpression = Expression.MakeBinary(type, memberExpression, rhs);

        return binaryExpression;
    }