(一)依赖的lamdb帮助类

public static class ExpressionBuilder
{
public static Expression<Func<T, bool>> And<T>(
this Expression<Func<T, bool>> first,
Expression<Func<T, bool>> second)
{
return first.AndAlso<T>(second, Expression.AndAlso);
}

public static Expression<Func<T, bool>> Or<T>(
this Expression<Func<T, bool>> first,
Expression<Func<T, bool>> second)
{
return first.AndAlso<T>(second, Expression.OrElse);
}

private static Expression<Func<T, bool>> AndAlso<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2, Func<Expression, Expression, BinaryExpression> func)
{
var parameter = Expression.Parameter(typeof(T));
//var parameter2 = Expression.Parameter(typeof(T));
var ddd = expr1.Parameters;
var leftVisitor = new ReplaceExpressionVisitor(expr1.Parameters[0], parameter);
var left = leftVisitor.Visit(expr1.Body);

var rightVisitor = new ReplaceExpressionVisitor(expr2.Parameters[0], parameter);//不是用.Parameters[0]结果是不对的
var right = rightVisitor.Visit(expr2.Body);

return Expression.Lambda<Func<T, bool>>(func(left, right), parameter);
///return Expression.Lambda(func(left, right), parameter);
}

private class ReplaceExpressionVisitor
: ExpressionVisitor
{
private readonly Expression _oldValue;
private readonly Expression _newValue;

public ReplaceExpressionVisitor(Expression oldValue, Expression newValue)
{
_oldValue = oldValue;
_newValue = newValue;
}

public override Expression Visit(Expression node)
{
if (node == _oldValue)
return _newValue;
return base.Visit(node);
}
}