我有两个简单的课程
class Band
include Mongoid::Document
field :name, type:String
has_many :members
end
class Member
include Mongoid::Document
field :name, type: String
belongs_to :band
end
在创建两个对象以进行测试之后
Band.create(title: 'New Band')
Band.members.create(name: 'New Member')
我得到了下一个数据库状态：
> db.bands.find()
{ "_id" : ObjectId("..."), "title" : "New Band" }
> db.members.find()
{ "_id" : ObjectId("..."), "name" : "New Member", "band_id" : ObjectId("...") }
当我尝试构建Band对象的json对象时，我得到的数据没有子级：
{"_id":"...","title":"New Band"}
但是我需要这样的东西：
{"_id":"...","title":"New Band", "members" : {"_id":"...","title":"New Member"}}
如何与孩子建立json？
我有两个priority_queue用float这样的：
std::priority_queue<float> queue1;
std::priority_queue<float> queue2;
我需要合并它们。但是 STLmerge算法不允许priority_queue直接使用：
merge(
queue1.begin(), queue2.end(),
queue2.begin(), queue2.end(),
queue1
);
有priority_queue没有不使用辅助数据结构的方式进行合并？
我有一个简单的链表类型和它的实现Clone:
#[deriving(Show)]
enum List {
Cons(int, Box<List>),
Nil,
}
impl Clone for List {
fn clone(&self) -> List {
match *self {
Cons(val, ref rest) => Cons(val, rest.clone()),
Nil => Nil,
}
}
}
它按预期工作.但是,如果我做我自己的MyClone特质与
相同签名
作为的Clone,我得到一个错误:
trait MyClone {
fn my_clone(&self) -> Self;
}
impl MyClone for List {
fn my_clone(&self) -> List {
match *self {
Cons(val, ref rest) => Cons(val, rest.my_clone()),
Nil => Nil,
}
}
}
.../src/main.rs:23:46: 23:61 error: mismatched …我有类似的类型Type<Param>.我如何在c ++ 11中检索Param？
可能是这样的:
// I know it's not correct but it conveys the idea very well
template
<
template <class Param> class Type
>
struct GetParam
{
typedef Param Result;
};
// e.g.
typedef GetParam<std::vector<double>>::Result X; // must return double
typedef GetParam<std::list<double>>::Result X; // double
typedef GetParam<std::vector<std::list<double>>::Result X; // std::list<double>
我在本地机器上创建了两个开发环境,并在heroku上创建了一个.
在这里我的'mongoid.yml':
development:
sessions:
default:
database: mydb_development
hosts:
- localhost:27017
staging:
sessions:
default:
database: mydb_staging
uri: <%= ENV['MONGOLAB_URI'] %>
Mongoid在本地机器上正常工作,但在heroku部署之后我接下来的错误:
/app/vendor/bundle/ruby/1.9.1/gems/mongoid-3.0.14/lib/mongoid/config/validators/session.rb:81:in `validate_session_uri': (Mongoid::Errors::MixedSessionConfiguration)
2012-12-25T10:12:44+00:00 app[web.1]: Problem:
2012-12-25T10:12:44+00:00 app[web.1]: Both uri and standard configuration options defined for session: 'default'.
2012-12-25T10:12:44+00:00 app[web.1]: Summary:
2012-12-25T10:12:44+00:00 app[web.1]: Instead of simply giving uri or standard options a preference order, Mongoid assumes that you have made a mistake in your configuration and requires that you provide one or the other, but not both. The options that …我有一个带验证的模型,如下所示:
class Order
include Mongoid::Document
field :first_name, type: String
field :last_name, type: String
validates_presence_of :first_name, :message => "Can't be empty"
validates_presence_of :last_name, :message => "Can't be empty"
end
我描述模型rspec和思想机器人shoulda:
describe Order do
# validations
it { should validate_presence_of(:first_name) }
it { should presence_of(:last_name) }
end
但是我失败了:
Failures:
1) Order
Failure/Error: it { should validate_presence_of(:first_name) }
Expected errors to include "can't be blank" when first_name is set to nil, got errors: ["first_name Can't be empty (nil)", …我有一个集合 db.events
Mongodb允许按日期范围进行查询(date0 <date1)
db.events.find({date:{$ gt:date0,$ lt:date1}})
它工作正常但我还需要使用超出范围的日期进行查询,例如在查询中
db.events.find({date:{$ or:[{$ lt:date0},{$ gt:date1}]})
但mongodb不允许上次查询"错误:无法使用$或使用日期."
那么,如何进行此类查询？
我有一个结构,通过next特征从方法给出数字Iterator:
struct Numbers{
number: usize,
count: usize
}
impl Iterator for Numbers {
type Item = usize;
fn next(&mut self) -> Option<Self::Item> {
if self.count > 0 {
self.count -= 1;
return Some(self.number);
}
return None;
}
}
fn main(){
let numbers = Numbers{
number: 777,
count: 10
};
for n in numbers {
println!{"{:?}", n};
}
}
它适用于usize类型.但是Box类型的相同代码会产生编译错误:
struct Numbers{
number: Box<usize>,
count: usize
}
impl Iterator for Numbers {
type Item = …我想创建MyViewModel它从网络获取数据然后更新结果数组。MyView应该订阅$model.results并显示List填充结果。
不幸的是，我收到一个关于“没有更多上下文的表达式类型不明确”的错误。
如何正确使用ForEach这种情况？
import SwiftUI
import Combine
class MyViewModel: ObservableObject {
@Published var results: [String] = []
init() {
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
self.results = ["Hello", "World", "!!!"]
}
}
}
struct MyView: View {
@ObservedObject var model: MyViewModel
var body: some View {
VStack {
List {
ForEach($model.results) { text in
Text(text)
// ^--- Type of expression is ambiguous without more context
}
}
}
}
}
struct …我在Javascript中面对数字数组的奇怪排序结果.例如排序[1,2,10,20,100,200]的结果:
> [1, 2, 10, 20, 100, 200].sort()
[ 1, 10, 100, 2, 20, 200 ]
为什么会这样？
似乎数组排序不能直接用于排序数值数组？