/// <summary>
/// Combines the first expression with the second using the specified merge function.
/// </summary>
static Expression <T> Compose <T>(this Expression <T> first, Expression <T> second, Func <Expression, Expression, Expression> merge)
{
// zip parameters (map from parameters of second to parameters of first)
var map = first.Parameters
.Select((f, i) => new { f, s = second.Parameters[i] })
.ToDictionary(p => p.s, p => p.f);
// replace parameters in the second lambda expression with the parameters in the first
var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
// create a merged lambda expression with parameters from the first expression
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
/// <summary>
/// 拼接or 条件语句
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="first"></param>
/// <param name="second"></param>
/// <returns></returns>
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > first, Expression <Func <T, bool> > second)
{
return(ParameterRebinder.Compose(first, second, Expression.Or));
}