更新
感谢Marc的帮助,AlphaPagedList类现在可以在CodePlex上获得,如果有兴趣的话请前往CodePlex
原始内容
我正在尝试创建一个表达式树来返回以给定字符开头的元素。
IList<char> chars = new List<char>{'a','b'};
IQueryable<Dept>Depts.Where(x=> chars.Contains(x.DeptName[0]));
我希望这个可以用于任何IEnumerable,其中我提供一个lambda来选择属性,例如:
Depts.Alpha(x=>x.DeptName, chars);
我一直在尝试,但完全没有成功,需要帮助吗?
public static IQueryable<T> testing<T>(this IQueryable<T> queryableData, Expression<Func<T,string>> pi, IEnumerable<char> chars)
{
// Compose the expression tree that represents the parameter to the predicate.
ParameterExpression pe = Expression.Parameter(queryableData.ElementType, "x");
ConstantExpression ch = Expression.Constant(chars,typeof(IEnumerable<char>));
// ***** Where(x=>chars.Contains(x.pi[0])) *****
// pi is a string property
//Get the string property
Expression first = Expression.Constant(0);
//Get the first character of the string
Expression firstchar = Expression.ArrayIndex(pi.Body, first);
//Call "Contains" on chars with argument being right
Expression e = Expression.Call(ch, typeof(IEnumerable<char>).GetMethod("Contains", new Type[] { typeof(char) }),firstchar);
MethodCallExpression whereCallExpression = Expression.Call(
typeof(Queryable),
"Where",
new Type[] { queryableData.ElementType },
queryableData.Expression,
Expression.Lambda<Func<T, bool>>(e, new ParameterExpression[] { pe }));
// ***** End Where *****
return (queryableData.Provider.CreateQuery<T>(whereCallExpression));
}