如何迭代groovy中的列表并为每个对象添加属性 [英] How to iterate over a list in groovy and add property for each object

问题描述

我有这样的事件列表：

events = Events.all

Events 通过类 UserEvents 与 Users 具有多对多关系。模仿方法spring-security-plugin ：

我想知道 User 是否参加 Event ，我可以这样做：

  UserEvent.get （currentUserId，eventId）
  

问题

如何在列表 events 的所有元素上做到这一点，以便在我的视图层中可以轻松找出 currentUserId 将会发生什么事？

解决方案

您可以查询所有关联的用户 s用于事件 code>像这样：



  def user = ... 
 def events = UserEvent.findAllByUser（user ）.event 
  

这是一个相当高效的查询，因为它执行的SQL类似于

  select * from user_event where user_id =？ 
  

然后加载每个事件。这是N + 1，因为它会逐个加载每个事件，因此您可以通过以下方法更高效地完成此操作：



  def eventIds = UserEvent.findAllByUser（user）.eventId 
 def events = Event.getAll（eventIds）
  

第一行只是使用与上面相同的SQL获取事件id，然后第二行运行SQL，如



  select * from event （？，？，？，...）
  




I have a list of events like so:

events = Events.all

Events have a many-to-many relationship with Users via class UserEvents modeled after the approach from spring-security-plugin:

I would like to find out whether a User is attending an Event and I can do that by running this:

UserEvent.get(currentUserId, eventId)

Question

How can I do this over all the elements of my list events so that in my view layer I can easily find out whether currentUserId is going to the event?

解决方案

You can query for all of the associated Users for an Event like this:

def user = ...
def events = UserEvent.findAllByUser(user).event

This is a fairly efficient query since it executes SQL similar to

select * from user_event where user_id=?

and then loads each Event. This is N+1 though since it loads each Event individually, so you can do it more efficiently with this:

def eventIds = UserEvent.findAllByUser(user).eventId
def events = Event.getAll(eventIds)

The first line just gets the event ids using the same SQL as above, then the second line runs SQL like

select * from event where id in (?, ?, ?, ...)

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