Expression<Func<T, bool>>

public static Expression<Func<T, bool>> True<T>() { return f => true; }

public static Expression<Func<T, bool>> False<T>() { return f => false; }

/// <summary>

/// 条件或

/// </summary>

/// <typeparam name="T"></typeparam>

/// <param name="expr1"></param>

/// <param name="expr2"></param>

/// <returns></returns>

public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,         Expression<Func<T, bool>> expr2)         {

var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());

return Expression.Lambda<Func<T, bool>>             (Expression.Or(expr1.Body, invokedExpr), expr1.Parameters);

}

/// <summary>

/// 条件且

/// </summary>

/// <typeparam name="T"></typeparam>

/// <param name="expr1"></param>

/// <param name="expr2"></param>

/// <returns></returns>

public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,         Expression<Func<T, bool>> expr2)         {

var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());

return Expression.Lambda<Func<T, bool>>

(Expression.And(expr1.Body, invokedExpr), expr1.Parameters);

}